tint/ast: Derive off `ast::Variable`

Add the new classes:
* `ast::Let`
* `ast::Override`
* `ast::Parameter`
* `ast::Var`

Limit the fields to those that are only applicable for their type.

Note: The resolver and validator is a tangled mess for each of the
variable types. This CL tries to keep the functionality exactly the
same. I'll clean this up in another change.

Bug: tint:1582
Change-Id: Iee83324167ffd4d92ae3032b2134677629c90079
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/93780
Reviewed-by: Dan Sinclair <dsinclair@chromium.org>
Commit-Queue: Ben Clayton <bclayton@chromium.org>
Kokoro: Kokoro <noreply+kokoro@google.com>

src/tint/BUILD.gn

@@ -264,6 +264,8 @@ libtint_source_set("libtint_core_all_src") {
     "ast/interpolate_attribute.h",
     "ast/invariant_attribute.cc",
     "ast/invariant_attribute.h",
+    "ast/let.cc",
+    "ast/let.h",
     "ast/literal_expression.cc",
     "ast/literal_expression.h",
     "ast/location_attribute.cc",
@@ -280,6 +282,10 @@ libtint_source_set("libtint_core_all_src") {
     "ast/multisampled_texture.h",
     "ast/node.cc",
     "ast/node.h",
+    "ast/override.cc",
+    "ast/override.h",
+    "ast/parameter.cc",
+    "ast/parameter.h",
     "ast/phony_expression.cc",
     "ast/phony_expression.h",
     "ast/pipeline_stage.cc",
@@ -328,6 +334,8 @@ libtint_source_set("libtint_core_all_src") {
     "ast/unary_op.h",
     "ast/unary_op_expression.cc",
     "ast/unary_op_expression.h",
+    "ast/var.cc",
+    "ast/var.h",
     "ast/variable.cc",
     "ast/variable.h",
     "ast/variable_decl_statement.cc",

src/tint/CMakeLists.txt

@@ -151,6 +151,8 @@ set(TINT_LIB_SRCS
   ast/interpolate_attribute.h
   ast/invariant_attribute.cc
   ast/invariant_attribute.h
+  ast/let.cc
+  ast/let.h
   ast/literal_expression.cc
   ast/literal_expression.h
   ast/location_attribute.cc
@@ -167,6 +169,10 @@ set(TINT_LIB_SRCS
   ast/multisampled_texture.h
   ast/node.cc
   ast/node.h
+  ast/override.cc
+  ast/override.h
+  ast/parameter.cc
+  ast/parameter.h
   ast/phony_expression.cc
   ast/phony_expression.h
   ast/pipeline_stage.cc
@@ -215,6 +221,8 @@ set(TINT_LIB_SRCS
   ast/unary_op_expression.h
   ast/unary_op.cc
   ast/unary_op.h
+  ast/var.cc
+  ast/var.h
   ast/variable_decl_statement.cc
   ast/variable_decl_statement.h
   ast/variable.cc

src/tint/ast/function.cc

@@ -40,7 +40,7 @@ Function::Function(ProgramID pid,
     TINT_ASSERT_PROGRAM_IDS_EQUAL_IF_VALID(AST, symbol, program_id);
     TINT_ASSERT_PROGRAM_IDS_EQUAL_IF_VALID(AST, body, program_id);
     for (auto* param : params) {
-        TINT_ASSERT(AST, param && param->is_const);
+        TINT_ASSERT(AST, tint::Is<Parameter>(param));
         TINT_ASSERT_PROGRAM_IDS_EQUAL_IF_VALID(AST, param, program_id);
     }
     TINT_ASSERT(AST, symbol.IsValid());

src/tint/ast/function.h

@@ -26,14 +26,11 @@
 #include "src/tint/ast/builtin_attribute.h"
 #include "src/tint/ast/group_attribute.h"
 #include "src/tint/ast/location_attribute.h"
+#include "src/tint/ast/parameter.h"
 #include "src/tint/ast/pipeline_stage.h"
-#include "src/tint/ast/variable.h"
 
 namespace tint::ast {
 
-/// ParameterList is a list of function parameters
-using ParameterList = std::vector<const Variable*>;
-
 /// A Function statement.
 class Function final : public Castable<Function, Node> {
   public:

src/tint/ast/function_test.cc

@@ -122,18 +122,6 @@ TEST_F(FunctionTest, Assert_DifferentProgramID_ReturnAttr) {
         "internal compiler error");
 }
 
-TEST_F(FunctionTest, Assert_NonConstParam) {
-    EXPECT_FATAL_FAILURE(
-        {
-            ProgramBuilder b;
-            ParameterList params;
-            params.push_back(b.Var("var", b.ty.i32(), ast::StorageClass::kNone));
-
-            b.Func("f", params, b.ty.void_(), {});
-        },
-        "internal compiler error");
-}
-
 using FunctionListTest = TestHelper;
 
 TEST_F(FunctionListTest, FindSymbol) {

src/tint/ast/let.cc

@@ -0,0 +1,46 @@
+// Copyright 2022 The Tint Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "src/tint/ast/let.h"
+
+#include "src/tint/program_builder.h"
+
+TINT_INSTANTIATE_TYPEINFO(tint::ast::Let);
+
+namespace tint::ast {
+
+Let::Let(ProgramID pid,
+         const Source& src,
+         const Symbol& sym,
+         const ast::Type* ty,
+         const Expression* ctor,
+         AttributeList attrs)
+    : Base(pid, src, sym, ty, ctor, attrs) {
+    TINT_ASSERT(AST, ctor != nullptr);
+}
+
+Let::Let(Let&&) = default;
+
+Let::~Let() = default;
+
+const Let* Let::Clone(CloneContext* ctx) const {
+    auto src = ctx->Clone(source);
+    auto sym = ctx->Clone(symbol);
+    auto* ty = ctx->Clone(type);
+    auto* ctor = ctx->Clone(constructor);
+    auto attrs = ctx->Clone(attributes);
+    return ctx->dst->create<Let>(src, sym, ty, ctor, attrs);
+}
+
+}  // namespace tint::ast

src/tint/ast/let.h

@@ -0,0 +1,61 @@
+// Copyright 2022 The Tint Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef SRC_TINT_AST_LET_H_
+#define SRC_TINT_AST_LET_H_
+
+#include "src/tint/ast/variable.h"
+
+namespace tint::ast {
+
+/// A "let" declaration is a name for a function-scoped runtime typed value.
+///
+/// Examples:
+///
+/// ```
+///   let twice_depth : i32 = width + width;  // Must have initializer
+/// ```
+/// @see https://www.w3.org/TR/WGSL/#let-decls
+class Let final : public Castable<Let, Variable> {
+  public:
+    /// Create a 'let' variable
+    /// @param program_id the identifier of the program that owns this node
+    /// @param source the variable source
+    /// @param sym the variable symbol
+    /// @param type the declared variable type
+    /// @param constructor the constructor expression
+    /// @param attributes the variable attributes
+    Let(ProgramID program_id,
+        const Source& source,
+        const Symbol& sym,
+        const ast::Type* type,
+        const Expression* constructor,
+        AttributeList attributes);
+
+    /// Move constructor
+    Let(Let&&);
+
+    /// Destructor
+    ~Let() override;
+
+    /// Clones this node and all transitive child nodes using the `CloneContext`
+    /// `ctx`.
+    /// @param ctx the clone context
+    /// @return the newly cloned node
+    const Let* Clone(CloneContext* ctx) const override;
+};
+
+}  // namespace tint::ast
+
+#endif  // SRC_TINT_AST_LET_H_

src/tint/ast/module.h

@@ -77,6 +77,19 @@ class Module final : public Castable<Module, Node> {
     /// @returns the global variables for the module
     VariableList& GlobalVariables() { return global_variables_; }
 
+    /// @returns the global variable declarations of kind 'T' for the module
+    template <typename T, typename = traits::EnableIfIsType<T, ast::Variable>>
+    std::vector<const T*> Globals() const {
+        std::vector<const T*> out;
+        out.reserve(global_variables_.size());
+        for (auto* global : global_variables_) {
+            if (auto* var = global->As<T>()) {
+                out.emplace_back(var);
+            }
+        }
+        return out;
+    }
+
     /// @returns the extension set for the module
     const EnableList& Enables() const { return enables_; }
 

src/tint/ast/override.cc

@@ -0,0 +1,44 @@
+// Copyright 2022 The Tint Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "src/tint/ast/override.h"
+
+#include "src/tint/program_builder.h"
+
+TINT_INSTANTIATE_TYPEINFO(tint::ast::Override);
+
+namespace tint::ast {
+
+Override::Override(ProgramID pid,
+                   const Source& src,
+                   const Symbol& sym,
+                   const ast::Type* ty,
+                   const Expression* ctor,
+                   AttributeList attrs)
+    : Base(pid, src, sym, ty, ctor, attrs) {}
+
+Override::Override(Override&&) = default;
+
+Override::~Override() = default;
+
+const Override* Override::Clone(CloneContext* ctx) const {
+    auto src = ctx->Clone(source);
+    auto sym = ctx->Clone(symbol);
+    auto* ty = ctx->Clone(type);
+    auto* ctor = ctx->Clone(constructor);
+    auto attrs = ctx->Clone(attributes);
+    return ctx->dst->create<Override>(src, sym, ty, ctor, attrs);
+}
+
+}  // namespace tint::ast

src/tint/ast/override.h

@@ -0,0 +1,62 @@
+// Copyright 2022 The Tint Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef SRC_TINT_AST_OVERRIDE_H_
+#define SRC_TINT_AST_OVERRIDE_H_
+
+#include "src/tint/ast/variable.h"
+
+namespace tint::ast {
+
+/// An "override" declaration - a name for a pipeline-overridable constant.
+/// Examples:
+///
+/// ```
+///   override radius : i32 = 2;       // Can be overridden by name.
+///   @id(5) override width : i32 = 2; // Can be overridden by ID.
+///   override scale : f32;            // No default - must be overridden.
+/// ```
+/// @see https://www.w3.org/TR/WGSL/#override-decls
+class Override final : public Castable<Override, Variable> {
+  public:
+    /// Create an 'override' pipeline-overridable constant.
+    /// @param program_id the identifier of the program that owns this node
+    /// @param source the variable source
+    /// @param sym the variable symbol
+    /// @param type the declared variable type
+    /// @param constructor the constructor expression
+    /// @param attributes the variable attributes
+    Override(ProgramID program_id,
+             const Source& source,
+             const Symbol& sym,
+             const ast::Type* type,
+             const Expression* constructor,
+             AttributeList attributes);
+
+    /// Move constructor
+    Override(Override&&);
+
+    /// Destructor
+    ~Override() override;
+
+    /// Clones this node and all transitive child nodes using the `CloneContext`
+    /// `ctx`.
+    /// @param ctx the clone context
+    /// @return the newly cloned node
+    const Override* Clone(CloneContext* ctx) const override;
+};
+
+}  // namespace tint::ast
+
+#endif  // SRC_TINT_AST_OVERRIDE_H_

src/tint/ast/parameter.cc

@@ -0,0 +1,42 @@
+// Copyright 2022 The Tint Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "src/tint/ast/parameter.h"
+
+#include "src/tint/program_builder.h"
+
+TINT_INSTANTIATE_TYPEINFO(tint::ast::Parameter);
+
+namespace tint::ast {
+
+Parameter::Parameter(ProgramID pid,
+                     const Source& src,
+                     const Symbol& sym,
+                     const ast::Type* ty,
+                     AttributeList attrs)
+    : Base(pid, src, sym, ty, nullptr, attrs) {}
+
+Parameter::Parameter(Parameter&&) = default;
+
+Parameter::~Parameter() = default;
+
+const Parameter* Parameter::Clone(CloneContext* ctx) const {
+    auto src = ctx->Clone(source);
+    auto sym = ctx->Clone(symbol);
+    auto* ty = ctx->Clone(type);
+    auto attrs = ctx->Clone(attributes);
+    return ctx->dst->create<Parameter>(src, sym, ty, attrs);
+}
+
+}  // namespace tint::ast

src/tint/ast/parameter.h

@@ -0,0 +1,66 @@
+// Copyright 2022 The Tint Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef SRC_TINT_AST_PARAMETER_H_
+#define SRC_TINT_AST_PARAMETER_H_
+
+#include <vector>
+
+#include "src/tint/ast/variable.h"
+
+namespace tint::ast {
+
+/// A formal parameter to a function - a name for a typed value to be passed into a function.
+/// Example:
+///
+/// ```
+///   fn twice(a: i32) -> i32 {  // "a:i32" is the formal parameter
+///     return a + a;
+///   }
+/// ```
+///
+/// @see https://www.w3.org/TR/WGSL/#creation-time-consts
+class Parameter final : public Castable<Parameter, Variable> {
+  public:
+    /// Create a 'parameter' creation-time value variable.
+    /// @param program_id the identifier of the program that owns this node
+    /// @param source the variable source
+    /// @param sym the variable symbol
+    /// @param type the declared variable type
+    /// @param attributes the variable attributes
+    Parameter(ProgramID program_id,
+              const Source& source,
+              const Symbol& sym,
+              const ast::Type* type,
+              AttributeList attributes);
+
+    /// Move constructor
+    Parameter(Parameter&&);
+
+    /// Destructor
+    ~Parameter() override;
+
+    /// Clones this node and all transitive child nodes using the `CloneContext`
+    /// `ctx`.
+    /// @param ctx the clone context
+    /// @return the newly cloned node
+    const Parameter* Clone(CloneContext* ctx) const override;
+};
+
+/// A list of parameters
+using ParameterList = std::vector<const Parameter*>;
+
+}  // namespace tint::ast
+
+#endif  // SRC_TINT_AST_PARAMETER_H_

src/tint/ast/var.cc

@@ -0,0 +1,49 @@
+// Copyright 2022 The Tint Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "src/tint/ast/var.h"
+
+#include "src/tint/program_builder.h"
+
+TINT_INSTANTIATE_TYPEINFO(tint::ast::Var);
+
+namespace tint::ast {
+
+Var::Var(ProgramID pid,
+         const Source& src,
+         const Symbol& sym,
+         const ast::Type* ty,
+         StorageClass storage_class,
+         Access access,
+         const Expression* ctor,
+         AttributeList attrs)
+    : Base(pid, src, sym, ty, ctor, attrs),
+      declared_storage_class(storage_class),
+      declared_access(access) {}
+
+Var::Var(Var&&) = default;
+
+Var::~Var() = default;
+
+const Var* Var::Clone(CloneContext* ctx) const {
+    auto src = ctx->Clone(source);
+    auto sym = ctx->Clone(symbol);
+    auto* ty = ctx->Clone(type);
+    auto* ctor = ctx->Clone(constructor);
+    auto attrs = ctx->Clone(attributes);
+    return ctx->dst->create<Var>(src, sym, ty, declared_storage_class, declared_access, ctor,
+                                 attrs);
+}
+
+}  // namespace tint::ast

src/tint/ast/var.h

@@ -0,0 +1,86 @@
+// Copyright 2022 The Tint Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef SRC_TINT_AST_VAR_H_
+#define SRC_TINT_AST_VAR_H_
+
+#include <utility>
+#include <vector>
+
+#include "src/tint/ast/variable.h"
+
+namespace tint::ast {
+
+/// A "var" declaration is a name for typed storage.
+///
+/// Examples:
+///
+/// ```
+///  // Declared outside a function, i.e. at module scope, requires
+///  // a storage class.
+///  var<workgroup> width : i32;     // no initializer
+///  var<private> height : i32 = 3;  // with initializer
+///
+///  // A variable declared inside a function doesn't take a storage class,
+///  // and maps to SPIR-V Function storage.
+///  var computed_depth : i32;
+///  var area : i32 = compute_area(width, height);
+/// ```
+///
+/// @see https://www.w3.org/TR/WGSL/#var-decls
+class Var final : public Castable<Var, Variable> {
+  public:
+    /// Create a 'var' variable
+    /// @param program_id the identifier of the program that owns this node
+    /// @param source the variable source
+    /// @param sym the variable symbol
+    /// @param type the declared variable type
+    /// @param declared_storage_class the declared storage class
+    /// @param declared_access the declared access control
+    /// @param constructor the constructor expression
+    /// @param attributes the variable attributes
+    Var(ProgramID program_id,
+        const Source& source,
+        const Symbol& sym,
+        const ast::Type* type,
+        StorageClass declared_storage_class,
+        Access declared_access,
+        const Expression* constructor,
+        AttributeList attributes);
+
+    /// Move constructor
+    Var(Var&&);
+
+    /// Destructor
+    ~Var() override;
+
+    /// Clones this node and all transitive child nodes using the `CloneContext`
+    /// `ctx`.
+    /// @param ctx the clone context
+    /// @return the newly cloned node
+    const Var* Clone(CloneContext* ctx) const override;
+
+    /// The declared storage class
+    const StorageClass declared_storage_class;
+
+    /// The declared access control
+    const Access declared_access;
+};
+
+/// A list of `var` declarations
+using VarList = std::vector<const Var*>;
+
+}  // namespace tint::ast
+
+#endif  // SRC_TINT_AST_VAR_H_

src/tint/ast/variable.cc

@@ -13,9 +13,8 @@
 // limitations under the License.
 
 #include "src/tint/ast/variable.h"
-
+#include "src/tint/ast/binding_attribute.h"
-#include "src/tint/program_builder.h"
+#include "src/tint/ast/group_attribute.h"
-#include "src/tint/sem/variable.h"
 
 TINT_INSTANTIATE_TYPEINFO(tint::ast::Variable);
 
@@ -24,24 +23,11 @@ namespace tint::ast {
 Variable::Variable(ProgramID pid,
                    const Source& src,
                    const Symbol& sym,
-                   StorageClass dsc,
-                   Access da,
                    const ast::Type* ty,
-                   bool constant,
-                   bool overridable,
                    const Expression* ctor,
                    AttributeList attrs)
-    : Base(pid, src),
+    : Base(pid, src), symbol(sym), type(ty), constructor(ctor), attributes(std::move(attrs)) {
-      symbol(sym),
-      type(ty),
-      is_const(constant),
-      is_overridable(overridable),
-      constructor(ctor),
-      attributes(std::move(attrs)),
-      declared_storage_class(dsc),
-      declared_access(da) {
     TINT_ASSERT(AST, symbol.IsValid());
-    TINT_ASSERT(AST, is_overridable ? is_const : true);
     TINT_ASSERT_PROGRAM_IDS_EQUAL_IF_VALID(AST, symbol, program_id);
     TINT_ASSERT_PROGRAM_IDS_EQUAL_IF_VALID(AST, constructor, program_id);
 }
@@ -54,23 +40,12 @@ VariableBindingPoint Variable::BindingPoint() const {
     const GroupAttribute* group = nullptr;
     const BindingAttribute* binding = nullptr;
     for (auto* attr : attributes) {
-        if (auto* g = attr->As<GroupAttribute>()) {
+        Switch(
-            group = g;
+            attr,  //
-        } else if (auto* b = attr->As<BindingAttribute>()) {
+            [&](const GroupAttribute* a) { group = a; },
-            binding = b;
+            [&](const BindingAttribute* a) { binding = a; });
-        }
     }
     return VariableBindingPoint{group, binding};
 }
 
-const Variable* Variable::Clone(CloneContext* ctx) const {
-    auto src = ctx->Clone(source);
-    auto sym = ctx->Clone(symbol);
-    auto* ty = ctx->Clone(type);
-    auto* ctor = ctx->Clone(constructor);
-    auto attrs = ctx->Clone(attributes);
-    return ctx->dst->create<Variable>(src, sym, declared_storage_class, declared_access, ty,
-                                      is_const, is_overridable, ctor, attrs);
-}
-
 }  // namespace tint::ast

src/tint/ast/variable.h

@@ -45,112 +45,38 @@ struct VariableBindingPoint {
     inline operator bool() const { return group && binding; }
 };
 
-/// A Variable statement.
+/// Variable is the base class for Var, Let, Const, Override and Parameter.
 ///
-/// An instance of this class represents one of four constructs in WGSL: "var"
+/// An instance of this class represents one of five constructs in WGSL: "var"  declaration, "let"
-/// declaration, "let" declaration, "override" declaration, or formal parameter
+/// declaration, "override" declaration, "const" declaration, or formal parameter to a function.
-/// to a function.
 ///
-/// 1. A "var" declaration is a name for typed storage.  Examples:
+/// @see https://www.w3.org/TR/WGSL/#value-decls
-///
+class Variable : public Castable<Variable, Node> {
-///       // Declared outside a function, i.e. at module scope, requires
-///       // a storage class.
-///       var<workgroup> width : i32;     // no initializer
-///       var<private> height : i32 = 3;  // with initializer
-///
-///       // A variable declared inside a function doesn't take a storage class,
-///       // and maps to SPIR-V Function storage.
-///       var computed_depth : i32;
-///       var area : i32 = compute_area(width, height);
-///
-/// 2. A "let" declaration is a name for a typed value.  Examples:
-///
-///       let twice_depth : i32 = width + width;  // Must have initializer
-///
-/// 3. An "override" declaration is a name for a pipeline-overridable constant.
-/// Examples:
-///
-///       override radius : i32 = 2;       // Can be overridden by name.
-///       @id(5) override width : i32 = 2; // Can be overridden by ID.
-///       override scale : f32;            // No default - must be overridden.
-///
-/// 4. A formal parameter to a function is a name for a typed value to
-///    be passed into a function.  Example:
-///
-///       fn twice(a: i32) -> i32 {  // "a:i32" is the formal parameter
-///         return a + a;
-///       }
-///
-/// From the WGSL draft, about "var"::
-///
-///   A variable is a named reference to storage that can contain a value of a
-///   particular type.
-///
-///   Two types are associated with a variable: its store type (the type of
-///   value that may be placed in the referenced storage) and its reference
-///   type (the type of the variable itself).  If a variable has store type T
-///   and storage class S, then its reference type is pointer-to-T-in-S.
-///
-/// This class uses the term "type" to refer to:
-///     the value type of a "let",
-///     the value type of an "override",
-///     the value type of the formal parameter,
-///     or the store type of the "var".
-//
-/// Setting is_const:
-///   - "var" gets false
-///   - "let" gets true
-///   - "override" gets true
-///   - formal parameter gets true
-///
-/// Setting is_overrideable:
-///   - "var" gets false
-///   - "let" gets false
-///   - "override" gets true
-///   - formal parameter gets false
-///
-/// Setting storage class:
-///   - "var" is StorageClass::kNone when using the
-///     defaulting syntax for a "var" declared inside a function.
-///   - "let" is always StorageClass::kNone.
-///   - formal parameter is always StorageClass::kNone.
-class Variable final : public Castable<Variable, Node> {
   public:
-    /// Create a variable
+    /// Constructor
     /// @param program_id the identifier of the program that owns this node
     /// @param source the variable source
     /// @param sym the variable symbol
-    /// @param declared_storage_class the declared storage class
-    /// @param declared_access the declared access control
     /// @param type the declared variable type
-    /// @param is_const true if the variable is const
-    /// @param is_overridable true if the variable is pipeline-overridable
     /// @param constructor the constructor expression
     /// @param attributes the variable attributes
     Variable(ProgramID program_id,
              const Source& source,
              const Symbol& sym,
-             StorageClass declared_storage_class,
-             Access declared_access,
              const ast::Type* type,
-             bool is_const,
-             bool is_overridable,
              const Expression* constructor,
              AttributeList attributes);
+
     /// Move constructor
     Variable(Variable&&);
 
+    /// Destructor
     ~Variable() override;
 
-    /// @returns the binding point information for the variable
+    /// @returns the binding point information from the variable's attributes.
+    /// @note binding points should only be applied to Var and Parameter types.
     VariableBindingPoint BindingPoint() const;
 
-    /// Clones this node and all transitive child nodes using the `CloneContext`
-    /// `ctx`.
-    /// @param ctx the clone context
-    /// @return the newly cloned node
-    const Variable* Clone(CloneContext* ctx) const override;
-
     /// The variable symbol
     const Symbol symbol;
 
@@ -159,23 +85,11 @@ class Variable final : public Castable<Variable, Node> {
     ///   var i = 1;
     const ast::Type* const type;
 
-    /// True if this is a constant, false otherwise
-    const bool is_const;
-
-    /// True if this is a pipeline-overridable constant, false otherwise
-    const bool is_overridable;
-
     /// The constructor expression or nullptr if none set
     const Expression* const constructor;
 
     /// The attributes attached to this variable
     const AttributeList attributes;
-
-    /// The declared storage class
-    const StorageClass declared_storage_class;
-
-    /// The declared access control
-    const Access declared_access;
 };
 
 /// A list of variables

src/tint/inspector/inspector.cc

@@ -183,7 +183,7 @@ std::vector<EntryPoint> Inspector::GetEntryPoints() {
             auto name = program_->Symbols().NameFor(decl->symbol);
 
             auto* global = var->As<sem::GlobalVariable>();
-            if (global && global->IsOverridable()) {
+            if (global && global->Declaration()->Is<ast::Override>()) {
                 OverridableConstant overridable_constant;
                 overridable_constant.name = name;
                 overridable_constant.numeric_id = global->ConstantId();
@@ -219,7 +219,7 @@ std::map<uint32_t, Scalar> Inspector::GetConstantIDs() {
     std::map<uint32_t, Scalar> result;
     for (auto* var : program_->AST().GlobalVariables()) {
         auto* global = program_->Sem().Get<sem::GlobalVariable>(var);
-        if (!global || !global->IsOverridable()) {
+        if (!global || !global->Declaration()->Is<ast::Override>()) {
             continue;
         }
 
@@ -276,7 +276,7 @@ std::map<std::string, uint32_t> Inspector::GetConstantNameToIdMap() {
     std::map<std::string, uint32_t> result;
     for (auto* var : program_->AST().GlobalVariables()) {
         auto* global = program_->Sem().Get<sem::GlobalVariable>(var);
-        if (global && global->IsOverridable()) {
+        if (global && global->Declaration()->Is<ast::Override>()) {
             auto name = program_->Symbols().NameFor(var->symbol);
             result[name] = global->ConstantId();
         }
@@ -813,25 +813,24 @@ void Inspector::GenerateSamplerTargets() {
         auto* t = c->args[texture_index];
         auto* s = c->args[sampler_index];
 
-        GetOriginatingResources(std::array<const ast::Expression*, 2>{t, s},
+        GetOriginatingResources(
-                                [&](std::array<const sem::GlobalVariable*, 2> globals) {
+            std::array<const ast::Expression*, 2>{t, s},
-                                    auto* texture = globals[0];
+            [&](std::array<const sem::GlobalVariable*, 2> globals) {
-                                    sem::BindingPoint texture_binding_point = {
+                auto* texture = globals[0]->Declaration()->As<ast::Var>();
-                                        texture->Declaration()->BindingPoint().group->value,
+                sem::BindingPoint texture_binding_point = {texture->BindingPoint().group->value,
-                                        texture->Declaration()->BindingPoint().binding->value};
+                                                           texture->BindingPoint().binding->value};
 
-                                    auto* sampler = globals[1];
+                auto* sampler = globals[1]->Declaration()->As<ast::Var>();
-                                    sem::BindingPoint sampler_binding_point = {
+                sem::BindingPoint sampler_binding_point = {sampler->BindingPoint().group->value,
-                                        sampler->Declaration()->BindingPoint().group->value,
+                                                           sampler->BindingPoint().binding->value};
-                                        sampler->Declaration()->BindingPoint().binding->value};
 
-                                    for (auto* entry_point : entry_points) {
+                for (auto* entry_point : entry_points) {
-                                        const auto& ep_name = program_->Symbols().NameFor(
+                    const auto& ep_name =
-                                            entry_point->Declaration()->symbol);
+                        program_->Symbols().NameFor(entry_point->Declaration()->symbol);
-                                        (*sampler_targets_)[ep_name].add(
+                    (*sampler_targets_)[ep_name].add(
-                                            {sampler_binding_point, texture_binding_point});
+                        {sampler_binding_point, texture_binding_point});
-                                    }
+                }
-                                });
+            });
     }
 }
 

src/tint/program_builder.h

@@ -53,11 +53,14 @@
 #include "src/tint/ast/index_accessor_expression.h"
 #include "src/tint/ast/interpolate_attribute.h"
 #include "src/tint/ast/invariant_attribute.h"
+#include "src/tint/ast/let.h"
 #include "src/tint/ast/loop_statement.h"
 #include "src/tint/ast/matrix.h"
 #include "src/tint/ast/member_accessor_expression.h"
 #include "src/tint/ast/module.h"
 #include "src/tint/ast/multisampled_texture.h"
+#include "src/tint/ast/override.h"
+#include "src/tint/ast/parameter.h"
 #include "src/tint/ast/phony_expression.h"
 #include "src/tint/ast/pointer.h"
 #include "src/tint/ast/return_statement.h"
@@ -73,6 +76,7 @@
 #include "src/tint/ast/type_name.h"
 #include "src/tint/ast/u32.h"
 #include "src/tint/ast/unary_op_expression.h"
+#include "src/tint/ast/var.h"
 #include "src/tint/ast/variable_decl_statement.h"
 #include "src/tint/ast/vector.h"
 #include "src/tint/ast/void.h"
@@ -1328,14 +1332,13 @@ class ProgramBuilder {
     ///   * ast::AttributeList - specifies the variable's attributes
     /// Note that repeated arguments of the same type will use the last argument's
     /// value.
-    /// @returns a `ast::Variable` with the given name, type and additional
+    /// @returns a `ast::Var` with the given name, type and additional
     /// options
     template <typename NAME, typename... OPTIONAL>
-    const ast::Variable* Var(NAME&& name, const ast::Type* type, OPTIONAL&&... optional) {
+    const ast::Var* Var(NAME&& name, const ast::Type* type, OPTIONAL&&... optional) {
         VarOptionals opts(std::forward<OPTIONAL>(optional)...);
-        return create<ast::Variable>(Sym(std::forward<NAME>(name)), opts.storage, opts.access, type,
+        return create<ast::Var>(Sym(std::forward<NAME>(name)), type, opts.storage, opts.access,
-                                     false /* is_const */, false /* is_overridable */,
+                                opts.constructor, std::move(opts.attributes));
-                                     opts.constructor, std::move(opts.attributes));
     }
 
     /// @param source the variable source
@@ -1349,32 +1352,28 @@ class ProgramBuilder {
     ///   * ast::AttributeList - specifies the variable's attributes
     /// Note that repeated arguments of the same type will use the last argument's
     /// value.
-    /// @returns a `ast::Variable` with the given name, storage and type
+    /// @returns a `ast::Var` with the given name, storage and type
     template <typename NAME, typename... OPTIONAL>
-    const ast::Variable* Var(const Source& source,
+    const ast::Var* Var(const Source& source,
-                             NAME&& name,
+                        NAME&& name,
-                             const ast::Type* type,
+                        const ast::Type* type,
-                             OPTIONAL&&... optional) {
+                        OPTIONAL&&... optional) {
         VarOptionals opts(std::forward<OPTIONAL>(optional)...);
-        return create<ast::Variable>(source, Sym(std::forward<NAME>(name)), opts.storage,
+        return create<ast::Var>(source, Sym(std::forward<NAME>(name)), type, opts.storage,
-                                     opts.access, type, false /* is_const */,
+                                opts.access, opts.constructor, std::move(opts.attributes));
-                                     false /* is_overridable */, opts.constructor,
-                                     std::move(opts.attributes));
     }
 
     /// @param name the variable name
     /// @param type the variable type
     /// @param constructor constructor expression
     /// @param attributes optional variable attributes
-    /// @returns an immutable `ast::Variable` with the given name and type
+    /// @returns an `ast::Let` with the given name and type
     template <typename NAME>
-    const ast::Variable* Let(NAME&& name,
+    const ast::Let* Let(NAME&& name,
-                             const ast::Type* type,
+                        const ast::Type* type,
-                             const ast::Expression* constructor,
+                        const ast::Expression* constructor,
-                             ast::AttributeList attributes = {}) {
+                        ast::AttributeList attributes = {}) {
-        return create<ast::Variable>(Sym(std::forward<NAME>(name)), ast::StorageClass::kNone,
+        return create<ast::Let>(Sym(std::forward<NAME>(name)), type, constructor, attributes);
-                                     ast::Access::kUndefined, type, true /* is_const */,
-                                     false /* is_overridable */, constructor, attributes);
     }
 
     /// @param source the variable source
@@ -1382,46 +1381,39 @@ class ProgramBuilder {
     /// @param type the variable type
     /// @param constructor constructor expression
     /// @param attributes optional variable attributes
-    /// @returns an immutable `ast::Variable` with the given name and type
+    /// @returns an `ast::Let` with the given name and type
     template <typename NAME>
-    const ast::Variable* Let(const Source& source,
+    const ast::Let* Let(const Source& source,
-                             NAME&& name,
+                        NAME&& name,
-                             const ast::Type* type,
+                        const ast::Type* type,
-                             const ast::Expression* constructor,
+                        const ast::Expression* constructor,
-                             ast::AttributeList attributes = {}) {
+                        ast::AttributeList attributes = {}) {
-        return create<ast::Variable>(source, Sym(std::forward<NAME>(name)),
+        return create<ast::Let>(source, Sym(std::forward<NAME>(name)), type, constructor,
-                                     ast::StorageClass::kNone, ast::Access::kUndefined, type,
+                                attributes);
-                                     true /* is_const */, false /* is_overridable */, constructor,
-                                     attributes);
     }
 
     /// @param name the parameter name
     /// @param type the parameter type
     /// @param attributes optional parameter attributes
-    /// @returns an immutable `ast::Variable` with the given name and type
+    /// @returns an `ast::Parameter` with the given name and type
     template <typename NAME>
-    const ast::Variable* Param(NAME&& name,
+    const ast::Parameter* Param(NAME&& name,
-                               const ast::Type* type,
+                                const ast::Type* type,
-                               ast::AttributeList attributes = {}) {
+                                ast::AttributeList attributes = {}) {
-        return create<ast::Variable>(Sym(std::forward<NAME>(name)), ast::StorageClass::kNone,
+        return create<ast::Parameter>(Sym(std::forward<NAME>(name)), type, attributes);
-                                     ast::Access::kUndefined, type, true /* is_const */,
-                                     false /* is_overridable */, nullptr, attributes);
     }
 
     /// @param source the parameter source
     /// @param name the parameter name
     /// @param type the parameter type
     /// @param attributes optional parameter attributes
-    /// @returns an immutable `ast::Variable` with the given name and type
+    /// @returns an `ast::Parameter` with the given name and type
     template <typename NAME>
-    const ast::Variable* Param(const Source& source,
+    const ast::Parameter* Param(const Source& source,
-                               NAME&& name,
+                                NAME&& name,
-                               const ast::Type* type,
+                                const ast::Type* type,
-                               ast::AttributeList attributes = {}) {
+                                ast::AttributeList attributes = {}) {
-        return create<ast::Variable>(source, Sym(std::forward<NAME>(name)),
+        return create<ast::Parameter>(source, Sym(std::forward<NAME>(name)), type, attributes);
-                                     ast::StorageClass::kNone, ast::Access::kUndefined, type,
-                                     true /* is_const */, false /* is_overridable */, nullptr,
-                                     attributes);
     }
 
     /// @param name the variable name
@@ -1434,10 +1426,10 @@ class ProgramBuilder {
     ///   * ast::AttributeList - specifies the variable's attributes
     /// Note that repeated arguments of the same type will use the last argument's
     /// value.
-    /// @returns a new `ast::Variable`, which is automatically registered as a
+    /// @returns a new `ast::Var`, which is automatically registered as a global variable with the
-    /// global variable with the ast::Module.
+    /// ast::Module.
     template <typename NAME, typename... OPTIONAL, typename = DisableIfSource<NAME>>
-    const ast::Variable* Global(NAME&& name, const ast::Type* type, OPTIONAL&&... optional) {
+    const ast::Var* Global(NAME&& name, const ast::Type* type, OPTIONAL&&... optional) {
         auto* var = Var(std::forward<NAME>(name), type, std::forward<OPTIONAL>(optional)...);
         AST().AddGlobalVariable(var);
         return var;
@@ -1454,13 +1446,13 @@ class ProgramBuilder {
     ///   * ast::AttributeList - specifies the variable's attributes
     /// Note that repeated arguments of the same type will use the last argument's
     /// value.
-    /// @returns a new `ast::Variable`, which is automatically registered as a
+    /// @returns a new `ast::Var`, which is automatically registered as a global variable with the
-    /// global variable with the ast::Module.
+    /// ast::Module.
     template <typename NAME, typename... OPTIONAL>
-    const ast::Variable* Global(const Source& source,
+    const ast::Var* Global(const Source& source,
-                                NAME&& name,
+                           NAME&& name,
-                                const ast::Type* type,
+                           const ast::Type* type,
-                                OPTIONAL&&... optional) {
+                           OPTIONAL&&... optional) {
         auto* var =
             Var(source, std::forward<NAME>(name), type, std::forward<OPTIONAL>(optional)...);
         AST().AddGlobalVariable(var);
@@ -1471,14 +1463,13 @@ class ProgramBuilder {
     /// @param type the variable type
     /// @param constructor constructor expression
     /// @param attributes optional variable attributes
-    /// @returns a const `ast::Variable` constructed by calling Var() with the
+    /// @returns an `ast::Let` constructed by calling Let() with the arguments of `args`, which is
-    /// arguments of `args`, which is automatically registered as a global
+    /// automatically registered as a global variable with the ast::Module.
-    /// variable with the ast::Module.
     template <typename NAME>
-    const ast::Variable* GlobalConst(NAME&& name,
+    const ast::Let* GlobalConst(NAME&& name,
-                                     const ast::Type* type,
+                                const ast::Type* type,
-                                     const ast::Expression* constructor,
+                                const ast::Expression* constructor,
-                                     ast::AttributeList attributes = {}) {
+                                ast::AttributeList attributes = {}) {
         auto* var = Let(std::forward<NAME>(name), type, constructor, std::move(attributes));
         AST().AddGlobalVariable(var);
         return var;
@@ -1489,15 +1480,15 @@ class ProgramBuilder {
     /// @param type the variable type
     /// @param constructor constructor expression
     /// @param attributes optional variable attributes
-    /// @returns a const `ast::Variable` constructed by calling Var() with the
+    /// @returns a const `ast::Let` constructed by calling Var() with the
     /// arguments of `args`, which is automatically registered as a global
     /// variable with the ast::Module.
     template <typename NAME>
-    const ast::Variable* GlobalConst(const Source& source,
+    const ast::Let* GlobalConst(const Source& source,
-                                     NAME&& name,
+                                NAME&& name,
-                                     const ast::Type* type,
+                                const ast::Type* type,
-                                     const ast::Expression* constructor,
+                                const ast::Expression* constructor,
-                                     ast::AttributeList attributes = {}) {
+                                ast::AttributeList attributes = {}) {
         auto* var = Let(source, std::forward<NAME>(name), type, constructor, std::move(attributes));
         AST().AddGlobalVariable(var);
         return var;
@@ -1507,17 +1498,15 @@ class ProgramBuilder {
     /// @param type the variable type
     /// @param constructor optional constructor expression
     /// @param attributes optional variable attributes
-    /// @returns an overridable const `ast::Variable` which is automatically
+    /// @returns an `ast::Override` which is automatically registered as a global variable with the
-    /// registered as a global variable with the ast::Module.
+    /// ast::Module.
     template <typename NAME>
-    const ast::Variable* Override(NAME&& name,
+    const ast::Override* Override(NAME&& name,
                                   const ast::Type* type,
                                   const ast::Expression* constructor,
                                   ast::AttributeList attributes = {}) {
-        auto* var =
+        auto* var = create<ast::Override>(source_, Sym(std::forward<NAME>(name)), type, constructor,
-            create<ast::Variable>(source_, Sym(std::forward<NAME>(name)), ast::StorageClass::kNone,
+                                          std::move(attributes));
-                                  ast::Access::kUndefined, type, true /* is_const */,
-                                  true /* is_overridable */, constructor, std::move(attributes));
         AST().AddGlobalVariable(var);
         return var;
     }
@@ -1527,19 +1516,16 @@ class ProgramBuilder {
     /// @param type the variable type
     /// @param constructor constructor expression
     /// @param attributes optional variable attributes
-    /// @returns a const `ast::Variable` constructed by calling Var() with the
+    /// @returns an `ast::Override` constructed with the arguments of `args`, which is automatically
-    /// arguments of `args`, which is automatically registered as a global
+    /// registered as a global variable with the ast::Module.
-    /// variable with the ast::Module.
     template <typename NAME>
-    const ast::Variable* Override(const Source& source,
+    const ast::Override* Override(const Source& source,
                                   NAME&& name,
                                   const ast::Type* type,
                                   const ast::Expression* constructor,
                                   ast::AttributeList attributes = {}) {
-        auto* var =
+        auto* var = create<ast::Override>(source, Sym(std::forward<NAME>(name)), type, constructor,
-            create<ast::Variable>(source, Sym(std::forward<NAME>(name)), ast::StorageClass::kNone,
+                                          std::move(attributes));
-                                  ast::Access::kUndefined, type, true /* is_const */,
-                                  true /* is_overridable */, constructor, std::move(attributes));
         AST().AddGlobalVariable(var);
         return var;
     }

src/tint/reader/spirv/function.cc

@@ -1253,12 +1253,12 @@ bool FunctionEmitter::EmitEntryPointAsWrapper() {
             auto* sample_mask_array_type = store_type->UnwrapRef()->UnwrapAlias()->As<Array>();
             TINT_ASSERT(Reader, sample_mask_array_type);
             ok = EmitPipelineInput(var_name, store_type, &param_decos, {0},
-                                   sample_mask_array_type->type, forced_param_type, &(decl.params),
+                                   sample_mask_array_type->type, forced_param_type, &decl.params,
                                    &stmts);
         } else {
             // The normal path.
             ok = EmitPipelineInput(var_name, store_type, &param_decos, {}, store_type,
-                                   forced_param_type, &(decl.params), &stmts);
+                                   forced_param_type, &decl.params, &stmts);
         }
         if (!ok) {
             return false;
@@ -1404,8 +1404,7 @@ bool FunctionEmitter::ParseFunctionDeclaration(FunctionDeclaration* decl) {
         auto* type = parser_impl_.ConvertType(param->type_id());
         if (type != nullptr) {
             auto* ast_param =
-                parser_impl_.MakeVariable(param->result_id(), ast::StorageClass::kNone, type, true,
+                parser_impl_.MakeParameter(param->result_id(), type, ast::AttributeList{});
-                                          false, nullptr, ast::AttributeList{});
             // Parameters are treated as const declarations.
             ast_params.emplace_back(ast_param);
             // The value is accessible by name.
@@ -2468,9 +2467,8 @@ bool FunctionEmitter::EmitFunctionVariables() {
                 return false;
             }
         }
-        auto* var =
+        auto* var = parser_impl_.MakeVar(inst.result_id(), ast::StorageClass::kNone, var_store_type,
-            parser_impl_.MakeVariable(inst.result_id(), ast::StorageClass::kNone, var_store_type,
+                                         constructor, ast::AttributeList{});
-                                      false, false, constructor, ast::AttributeList{});
         auto* var_decl_stmt = create<ast::VariableDeclStatement>(Source{}, var);
         AddStatement(var_decl_stmt);
         auto* var_type = ty_.Reference(var_store_type, ast::StorageClass::kNone);
@@ -3328,8 +3326,8 @@ bool FunctionEmitter::EmitStatementsInBasicBlock(const BlockInfo& block_info,
         TINT_ASSERT(Reader, def_inst);
         auto* storage_type = RemapStorageClass(parser_impl_.ConvertType(def_inst->type_id()), id);
         AddStatement(create<ast::VariableDeclStatement>(
-            Source{}, parser_impl_.MakeVariable(id, ast::StorageClass::kNone, storage_type, false,
+            Source{}, parser_impl_.MakeVar(id, ast::StorageClass::kNone, storage_type, nullptr,
-                                                false, nullptr, ast::AttributeList{})));
+                                           ast::AttributeList{})));
         auto* type = ty_.Reference(storage_type, ast::StorageClass::kNone);
         identifier_types_.emplace(id, type);
     }
@@ -3396,13 +3394,11 @@ bool FunctionEmitter::EmitConstDefinition(const spvtools::opt::Instruction& inst
     }
 
     expr = AddressOfIfNeeded(expr, &inst);
-    auto* ast_const =
+    auto* let = parser_impl_.MakeLet(inst.result_id(), expr.type, expr.expr);
-        parser_impl_.MakeVariable(inst.result_id(), ast::StorageClass::kNone, expr.type, true,
+    if (!let) {
-                                  false, expr.expr, ast::AttributeList{});
-    if (!ast_const) {
         return false;
     }
-    AddStatement(create<ast::VariableDeclStatement>(Source{}, ast_const));
+    AddStatement(create<ast::VariableDeclStatement>(Source{}, let));
     identifier_types_.emplace(inst.result_id(), expr.type);
     return success();
 }

src/tint/reader/spirv/parser_impl.cc

@@ -1371,8 +1371,8 @@ bool ParserImpl::EmitScalarSpecConstants() {
                     break;
                 }
             }
-            auto* ast_var = MakeVariable(inst.result_id(), ast::StorageClass::kNone, ast_type, true,
+            auto* ast_var =
-                                         true, ast_expr, std::move(spec_id_decos));
+                MakeOverride(inst.result_id(), ast_type, ast_expr, std::move(spec_id_decos));
             if (ast_var) {
                 builder_.AST().AddGlobalVariable(ast_var);
                 scalar_spec_constants_.insert(inst.result_id());
@@ -1489,8 +1489,8 @@ bool ParserImpl::EmitModuleScopeVariables() {
             // here.)
             ast_constructor = MakeConstantExpression(var.GetSingleWordInOperand(1)).expr;
         }
-        auto* ast_var = MakeVariable(var.result_id(), ast_storage_class, ast_store_type, false,
+        auto* ast_var = MakeVar(var.result_id(), ast_storage_class, ast_store_type, ast_constructor,
-                                     false, ast_constructor, ast::AttributeList{});
+                                ast::AttributeList{});
         // TODO(dneto): initializers (a.k.a. constructor expression)
         if (ast_var) {
             builder_.AST().AddGlobalVariable(ast_var);
@@ -1521,10 +1521,9 @@ bool ParserImpl::EmitModuleScopeVariables() {
             }
         }
         auto* ast_var =
-            MakeVariable(builtin_position_.per_vertex_var_id,
+            MakeVar(builtin_position_.per_vertex_var_id,
-                         enum_converter_.ToStorageClass(builtin_position_.storage_class),
+                    enum_converter_.ToStorageClass(builtin_position_.storage_class),
-                         ConvertType(builtin_position_.position_member_type_id), false, false,
+                    ConvertType(builtin_position_.position_member_type_id), ast_constructor, {});
-                         ast_constructor, {});
 
         builder_.AST().AddGlobalVariable(ast_var);
     }
@@ -1554,13 +1553,11 @@ const spvtools::opt::analysis::IntConstant* ParserImpl::GetArraySize(uint32_t va
     return size->AsIntConstant();
 }
 
-ast::Variable* ParserImpl::MakeVariable(uint32_t id,
+ast::Var* ParserImpl::MakeVar(uint32_t id,
-                                        ast::StorageClass sc,
+                              ast::StorageClass sc,
-                                        const Type* storage_type,
+                              const Type* storage_type,
-                                        bool is_const,
+                              const ast::Expression* constructor,
-                                        bool is_overridable,
+                              ast::AttributeList decorations) {
-                                        const ast::Expression* constructor,
-                                        ast::AttributeList decorations) {
     if (storage_type == nullptr) {
         Fail() << "internal error: can't make ast::Variable for null type";
         return nullptr;
@@ -1588,15 +1585,37 @@ ast::Variable* ParserImpl::MakeVariable(uint32_t id,
         return nullptr;
     }
 
-    std::string name = namer_.Name(id);
+    auto sym = builder_.Symbols().Register(namer_.Name(id));
+    return create<ast::Var>(Source{}, sym, storage_type->Build(builder_), sc, access, constructor,
+                            decorations);
+}
 
-    // Note: we're constructing the variable here with the *storage* type,
+ast::Let* ParserImpl::MakeLet(uint32_t id, const Type* type, const ast::Expression* constructor) {
-    // regardless of whether this is a `let`, `override`, or `var` declaration.
+    auto sym = builder_.Symbols().Register(namer_.Name(id));
-    // `var` declarations will have a resolved type of ref<storage>, but at the
+    return create<ast::Let>(Source{}, sym, type->Build(builder_), constructor,
-    // AST level all three are declared with the same type.
+                            ast::AttributeList{});
-    return create<ast::Variable>(Source{}, builder_.Symbols().Register(name), sc, access,
+}
-                                 storage_type->Build(builder_), is_const, is_overridable,
+
-                                 constructor, decorations);
+ast::Override* ParserImpl::MakeOverride(uint32_t id,
+                                        const Type* type,
+                                        const ast::Expression* constructor,
+                                        ast::AttributeList decorations) {
+    if (!ConvertDecorationsForVariable(id, &type, &decorations, false)) {
+        return nullptr;
+    }
+    auto sym = builder_.Symbols().Register(namer_.Name(id));
+    return create<ast::Override>(Source{}, sym, type->Build(builder_), constructor, decorations);
+}
+
+ast::Parameter* ParserImpl::MakeParameter(uint32_t id,
+                                          const Type* type,
+                                          ast::AttributeList decorations) {
+    if (!ConvertDecorationsForVariable(id, &type, &decorations, false)) {
+        return nullptr;
+    }
+
+    auto sym = builder_.Symbols().Register(namer_.Name(id));
+    return create<ast::Parameter>(Source{}, sym, type->Build(builder_), decorations);
 }
 
 bool ParserImpl::ConvertDecorationsForVariable(uint32_t id,

src/tint/reader/spirv/parser_impl.h

@@ -411,25 +411,47 @@ class ParserImpl : Reader {
     /// @returns a list of SPIR-V decorations.
     DecorationList GetMemberPipelineDecorations(const Struct& struct_type, int member_index);
 
-    /// Creates an AST Variable node for a SPIR-V ID, including any attached
+    /// Creates an AST 'var' node for a SPIR-V ID, including any attached decorations, unless it's
-    /// decorations, unless it's an ignorable builtin variable.
+    /// an ignorable builtin variable.
     /// @param id the SPIR-V result ID
     /// @param sc the storage class, which cannot be ast::StorageClass::kNone
     /// @param storage_type the storage type of the variable
-    /// @param is_const if true, the variable is const
-    /// @param is_overridable if true, the variable is pipeline-overridable
     /// @param constructor the variable constructor
     /// @param decorations the variable decorations
     /// @returns a new Variable node, or null in the ignorable variable case and
     /// in the error case
-    ast::Variable* MakeVariable(uint32_t id,
+    ast::Var* MakeVar(uint32_t id,
-                                ast::StorageClass sc,
+                      ast::StorageClass sc,
-                                const Type* storage_type,
+                      const Type* storage_type,
-                                bool is_const,
+                      const ast::Expression* constructor,
-                                bool is_overridable,
+                      ast::AttributeList decorations);
+
+    /// Creates an AST 'let' node for a SPIR-V ID, including any attached decorations,.
+    /// @param id the SPIR-V result ID
+    /// @param type the type of the variable
+    /// @param constructor the variable constructor
+    /// @returns the AST 'let' node
+    ast::Let* MakeLet(uint32_t id, const Type* type, const ast::Expression* constructor);
+
+    /// Creates an AST 'override' node for a SPIR-V ID, including any attached decorations.
+    /// @param id the SPIR-V result ID
+    /// @param type the type of the variable
+    /// @param constructor the variable constructor
+    /// @param decorations the variable decorations
+    /// @returns the AST 'override' node
+    ast::Override* MakeOverride(uint32_t id,
+                                const Type* type,
                                 const ast::Expression* constructor,
                                 ast::AttributeList decorations);
 
+    /// Creates an AST parameter node for a SPIR-V ID, including any attached decorations, unless
+    /// it's an ignorable builtin variable.
+    /// @param id the SPIR-V result ID
+    /// @param type the type of the parameter
+    /// @param decorations the parameter decorations
+    /// @returns the AST parameter node
+    ast::Parameter* MakeParameter(uint32_t id, const Type* type, ast::AttributeList decorations);
+
     /// Returns true if a constant expression can be generated.
     /// @param id the SPIR-V ID of the value
     /// @returns true if a constant expression can be generated

src/tint/reader/wgsl/parser_impl.cc

@@ -213,7 +213,11 @@ ParserImpl::FunctionHeader::FunctionHeader(Source src,
                                            ast::ParameterList p,
                                            const ast::Type* ret_ty,
                                            ast::AttributeList ret_attrs)
-    : source(src), name(n), params(p), return_type(ret_ty), return_type_attributes(ret_attrs) {}
+    : source(src),
+      name(n),
+      params(std::move(p)),
+      return_type(ret_ty),
+      return_type_attributes(std::move(ret_attrs)) {}
 
 ParserImpl::FunctionHeader::~FunctionHeader() = default;
 
@@ -542,15 +546,13 @@ Maybe<const ast::Variable*> ParserImpl::global_variable_decl(ast::AttributeList&
         constructor = expr.value;
     }
 
-    return create<ast::Variable>(decl->source,                             // source
+    return create<ast::Var>(decl->source,                             // source
-                                 builder_.Symbols().Register(decl->name),  // symbol
+                            builder_.Symbols().Register(decl->name),  // symbol
-                                 decl->storage_class,                      // storage class
+                            decl->type,                               // type
-                                 decl->access,                             // access control
+                            decl->storage_class,                      // storage class
-                                 decl->type,                               // type
+                            decl->access,                             // access control
-                                 false,                                    // is_const
+                            constructor,                              // constructor
-                                 false,                                    // is_overridable
+                            std::move(attrs));                        // attributes
-                                 constructor,                              // constructor
-                                 std::move(attrs));                        // attributes
 }
 
 // global_constant_decl :
@@ -564,7 +566,7 @@ Maybe<const ast::Variable*> ParserImpl::global_constant_decl(ast::AttributeList&
     if (match(Token::Type::kLet)) {
         use = "'let' declaration";
     } else if (match(Token::Type::kOverride)) {
-        use = "override declaration";
+        use = "'override' declaration";
         is_overridable = true;
     } else {
         return Failure::kNoMatch;
@@ -594,15 +596,18 @@ Maybe<const ast::Variable*> ParserImpl::global_constant_decl(ast::AttributeList&
         initializer = std::move(init.value);
     }
 
-    return create<ast::Variable>(decl->source,                             // source
+    if (is_overridable) {
-                                 builder_.Symbols().Register(decl->name),  // symbol
+        return create<ast::Override>(decl->source,                             // source
-                                 ast::StorageClass::kNone,                 // storage class
+                                     builder_.Symbols().Register(decl->name),  // symbol
-                                 ast::Access::kUndefined,                  // access control
+                                     decl->type,                               // type
-                                 decl->type,                               // type
+                                     initializer,                              // constructor
-                                 true,                                     // is_const
+                                     std::move(attrs));                        // attributes
-                                 is_overridable,                           // is_overridable
+    }
-                                 initializer,                              // constructor
+    return create<ast::Let>(decl->source,                             // source
-                                 std::move(attrs));                        // attributes
+                            builder_.Symbols().Register(decl->name),  // symbol
+                            decl->type,                               // type
+                            initializer,                              // constructor
+                            std::move(attrs));                        // attributes
 }
 
 // variable_decl
@@ -1478,7 +1483,7 @@ Expect<ast::ParameterList> ParserImpl::expect_param_list() {
 
 // param
 //   : attribute_list* variable_ident_decl
-Expect<ast::Variable*> ParserImpl::expect_param() {
+Expect<ast::Parameter*> ParserImpl::expect_param() {
     auto attrs = attribute_list();
 
     auto decl = expect_variable_ident_decl("parameter");
@@ -1486,21 +1491,10 @@ Expect<ast::Variable*> ParserImpl::expect_param() {
         return Failure::kErrored;
     }
 
-    auto* var = create<ast::Variable>(decl->source,                             // source
+    return create<ast::Parameter>(decl->source,                             // source
-                                      builder_.Symbols().Register(decl->name),  // symbol
+                                  builder_.Symbols().Register(decl->name),  // symbol
-                                      ast::StorageClass::kNone,                 // storage class
+                                  decl->type,                               // type
-                                      ast::Access::kUndefined,                  // access control
+                                  std::move(attrs.value));                  // attributes
-                                      decl->type,                               // type
-                                      true,                                     // is_const
-                                      false,                                    // is_overridable
-                                      nullptr,                                  // constructor
-                                      std::move(attrs.value));                  // attributes
-    // Formal parameters are treated like a const declaration where the
-    // initializer value is provided by the call's argument.  The key point is
-    // that it's not updatable after initially set.  This is unlike C or GLSL
-    // which treat formal parameters like local variables that can be updated.
-
-    return var;
 }
 
 // pipeline_stage
@@ -1794,17 +1788,13 @@ Maybe<const ast::VariableDeclStatement*> ParserImpl::variable_stmt() {
             return add_error(peek(), "missing constructor for 'let' declaration");
         }
 
-        auto* var = create<ast::Variable>(decl->source,                             // source
+        auto* let = create<ast::Let>(decl->source,                             // source
-                                          builder_.Symbols().Register(decl->name),  // symbol
+                                     builder_.Symbols().Register(decl->name),  // symbol
-                                          ast::StorageClass::kNone,                 // storage class
+                                     decl->type,                               // type
-                                          ast::Access::kUndefined,  // access control
+                                     constructor.value,                        // constructor
-                                          decl->type,               // type
+                                     ast::AttributeList{});                    // attributes
-                                          true,                     // is_const
-                                          false,                    // is_overridable
-                                          constructor.value,        // constructor
-                                          ast::AttributeList{});    // attributes
 
-        return create<ast::VariableDeclStatement>(decl->source, var);
+        return create<ast::VariableDeclStatement>(decl->source, let);
     }
 
     auto decl = variable_decl(/*allow_inferred = */ true);
@@ -1828,15 +1818,13 @@ Maybe<const ast::VariableDeclStatement*> ParserImpl::variable_stmt() {
         constructor = constructor_expr.value;
     }
 
-    auto* var = create<ast::Variable>(decl->source,                             // source
+    auto* var = create<ast::Var>(decl->source,                             // source
-                                      builder_.Symbols().Register(decl->name),  // symbol
+                                 builder_.Symbols().Register(decl->name),  // symbol
-                                      decl->storage_class,                      // storage class
+                                 decl->type,                               // type
-                                      decl->access,                             // access control
+                                 decl->storage_class,                      // storage class
-                                      decl->type,                               // type
+                                 decl->access,                             // access control
-                                      false,                                    // is_const
+                                 constructor,                              // constructor
-                                      false,                                    // is_overridable
+                                 ast::AttributeList{});                    // attributes
-                                      constructor,                              // constructor
-                                      ast::AttributeList{});                    // attributes
 
     return create<ast::VariableDeclStatement>(var->source, var);
 }

src/tint/reader/wgsl/parser_impl.h

@@ -462,7 +462,7 @@ class ParserImpl {
     Expect<ast::ParameterList> expect_param_list();
     /// Parses a `param` grammar element, erroring on parse failure.
     /// @returns the parsed variable
-    Expect<ast::Variable*> expect_param();
+    Expect<ast::Parameter*> expect_param();
     /// Parses a `pipeline_stage` grammar element, erroring if the next token does
     /// not match a stage name.
     /// @returns the pipeline stage.

src/tint/reader/wgsl/parser_impl_for_stmt_test.cc

@@ -57,7 +57,7 @@ TEST_F(ForStmtTest, InitializerStatementDecl) {
     ASSERT_TRUE(fl.matched);
     ASSERT_TRUE(Is<ast::VariableDeclStatement>(fl->initializer));
     auto* var = fl->initializer->As<ast::VariableDeclStatement>()->variable;
-    EXPECT_FALSE(var->is_const);
+    EXPECT_TRUE(var->Is<ast::Var>());
     EXPECT_EQ(var->constructor, nullptr);
     EXPECT_EQ(fl->condition, nullptr);
     EXPECT_EQ(fl->continuing, nullptr);
@@ -74,7 +74,7 @@ TEST_F(ForStmtTest, InitializerStatementDeclEqual) {
     ASSERT_TRUE(fl.matched);
     ASSERT_TRUE(Is<ast::VariableDeclStatement>(fl->initializer));
     auto* var = fl->initializer->As<ast::VariableDeclStatement>()->variable;
-    EXPECT_FALSE(var->is_const);
+    EXPECT_TRUE(var->Is<ast::Var>());
     EXPECT_NE(var->constructor, nullptr);
     EXPECT_EQ(fl->condition, nullptr);
     EXPECT_EQ(fl->continuing, nullptr);
@@ -90,7 +90,7 @@ TEST_F(ForStmtTest, InitializerStatementConstDecl) {
     ASSERT_TRUE(fl.matched);
     ASSERT_TRUE(Is<ast::VariableDeclStatement>(fl->initializer));
     auto* var = fl->initializer->As<ast::VariableDeclStatement>()->variable;
-    EXPECT_TRUE(var->is_const);
+    EXPECT_TRUE(var->Is<ast::Let>());
     EXPECT_NE(var->constructor, nullptr);
     EXPECT_EQ(fl->condition, nullptr);
     EXPECT_EQ(fl->continuing, nullptr);

src/tint/reader/wgsl/parser_impl_global_constant_decl_test.cc

@@ -27,21 +27,20 @@ TEST_F(ParserImplTest, GlobalConstantDecl) {
     EXPECT_FALSE(p->has_error()) << p->error();
     EXPECT_TRUE(e.matched);
     EXPECT_FALSE(e.errored);
-    ASSERT_NE(e.value, nullptr);
+    auto* let = e.value->As<ast::Let>();
+    ASSERT_NE(let, nullptr);
 
-    EXPECT_TRUE(e->is_const);
+    EXPECT_EQ(let->symbol, p->builder().Symbols().Get("a"));
-    EXPECT_FALSE(e->is_overridable);
+    ASSERT_NE(let->type, nullptr);
-    EXPECT_EQ(e->symbol, p->builder().Symbols().Get("a"));
+    EXPECT_TRUE(let->type->Is<ast::F32>());
-    ASSERT_NE(e->type, nullptr);
-    EXPECT_TRUE(e->type->Is<ast::F32>());
 
-    EXPECT_EQ(e->source.range.begin.line, 1u);
+    EXPECT_EQ(let->source.range.begin.line, 1u);
-    EXPECT_EQ(e->source.range.begin.column, 5u);
+    EXPECT_EQ(let->source.range.begin.column, 5u);
-    EXPECT_EQ(e->source.range.end.line, 1u);
+    EXPECT_EQ(let->source.range.end.line, 1u);
-    EXPECT_EQ(e->source.range.end.column, 6u);
+    EXPECT_EQ(let->source.range.end.column, 6u);
 
-    ASSERT_NE(e->constructor, nullptr);
+    ASSERT_NE(let->constructor, nullptr);
-    EXPECT_TRUE(e->constructor->Is<ast::LiteralExpression>());
+    EXPECT_TRUE(let->constructor->Is<ast::LiteralExpression>());
 }
 
 TEST_F(ParserImplTest, GlobalConstantDecl_Inferred) {
@@ -53,20 +52,19 @@ TEST_F(ParserImplTest, GlobalConstantDecl_Inferred) {
     EXPECT_FALSE(p->has_error()) << p->error();
     EXPECT_TRUE(e.matched);
     EXPECT_FALSE(e.errored);
-    ASSERT_NE(e.value, nullptr);
+    auto* let = e.value->As<ast::Let>();
+    ASSERT_NE(let, nullptr);
 
-    EXPECT_TRUE(e->is_const);
+    EXPECT_EQ(let->symbol, p->builder().Symbols().Get("a"));
-    EXPECT_FALSE(e->is_overridable);
+    EXPECT_EQ(let->type, nullptr);
-    EXPECT_EQ(e->symbol, p->builder().Symbols().Get("a"));
-    EXPECT_EQ(e->type, nullptr);
 
-    EXPECT_EQ(e->source.range.begin.line, 1u);
+    EXPECT_EQ(let->source.range.begin.line, 1u);
-    EXPECT_EQ(e->source.range.begin.column, 5u);
+    EXPECT_EQ(let->source.range.begin.column, 5u);
-    EXPECT_EQ(e->source.range.end.line, 1u);
+    EXPECT_EQ(let->source.range.end.line, 1u);
-    EXPECT_EQ(e->source.range.end.column, 6u);
+    EXPECT_EQ(let->source.range.end.column, 6u);
 
-    ASSERT_NE(e->constructor, nullptr);
+    ASSERT_NE(let->constructor, nullptr);
-    EXPECT_TRUE(e->constructor->Is<ast::LiteralExpression>());
+    EXPECT_TRUE(let->constructor->Is<ast::LiteralExpression>());
 }
 
 TEST_F(ParserImplTest, GlobalConstantDecl_InvalidExpression) {
@@ -105,23 +103,22 @@ TEST_F(ParserImplTest, GlobalConstantDec_Override_WithId) {
     EXPECT_FALSE(p->has_error()) << p->error();
     EXPECT_TRUE(e.matched);
     EXPECT_FALSE(e.errored);
-    ASSERT_NE(e.value, nullptr);
+    auto* override = e.value->As<ast::Override>();
+    ASSERT_NE(override, nullptr);
 
-    EXPECT_TRUE(e->is_const);
+    EXPECT_EQ(override->symbol, p->builder().Symbols().Get("a"));
-    EXPECT_TRUE(e->is_overridable);
+    ASSERT_NE(override->type, nullptr);
-    EXPECT_EQ(e->symbol, p->builder().Symbols().Get("a"));
+    EXPECT_TRUE(override->type->Is<ast::F32>());
-    ASSERT_NE(e->type, nullptr);
-    EXPECT_TRUE(e->type->Is<ast::F32>());
 
-    EXPECT_EQ(e->source.range.begin.line, 1u);
+    EXPECT_EQ(override->source.range.begin.line, 1u);
-    EXPECT_EQ(e->source.range.begin.column, 17u);
+    EXPECT_EQ(override->source.range.begin.column, 17u);
-    EXPECT_EQ(e->source.range.end.line, 1u);
+    EXPECT_EQ(override->source.range.end.line, 1u);
-    EXPECT_EQ(e->source.range.end.column, 18u);
+    EXPECT_EQ(override->source.range.end.column, 18u);
 
-    ASSERT_NE(e->constructor, nullptr);
+    ASSERT_NE(override->constructor, nullptr);
-    EXPECT_TRUE(e->constructor->Is<ast::LiteralExpression>());
+    EXPECT_TRUE(override->constructor->Is<ast::LiteralExpression>());
 
-    auto* override_attr = ast::GetAttribute<ast::IdAttribute>(e.value->attributes);
+    auto* override_attr = ast::GetAttribute<ast::IdAttribute>(override->attributes);
     ASSERT_NE(override_attr, nullptr);
     EXPECT_EQ(override_attr->value, 7u);
 }
@@ -136,23 +133,22 @@ TEST_F(ParserImplTest, GlobalConstantDec_Override_WithoutId) {
     EXPECT_FALSE(p->has_error()) << p->error();
     EXPECT_TRUE(e.matched);
     EXPECT_FALSE(e.errored);
-    ASSERT_NE(e.value, nullptr);
+    auto* override = e.value->As<ast::Override>();
+    ASSERT_NE(override, nullptr);
 
-    EXPECT_TRUE(e->is_const);
+    EXPECT_EQ(override->symbol, p->builder().Symbols().Get("a"));
-    EXPECT_TRUE(e->is_overridable);
+    ASSERT_NE(override->type, nullptr);
-    EXPECT_EQ(e->symbol, p->builder().Symbols().Get("a"));
+    EXPECT_TRUE(override->type->Is<ast::F32>());
-    ASSERT_NE(e->type, nullptr);
-    EXPECT_TRUE(e->type->Is<ast::F32>());
 
-    EXPECT_EQ(e->source.range.begin.line, 1u);
+    EXPECT_EQ(override->source.range.begin.line, 1u);
-    EXPECT_EQ(e->source.range.begin.column, 10u);
+    EXPECT_EQ(override->source.range.begin.column, 10u);
-    EXPECT_EQ(e->source.range.end.line, 1u);
+    EXPECT_EQ(override->source.range.end.line, 1u);
-    EXPECT_EQ(e->source.range.end.column, 11u);
+    EXPECT_EQ(override->source.range.end.column, 11u);
 
-    ASSERT_NE(e->constructor, nullptr);
+    ASSERT_NE(override->constructor, nullptr);
-    EXPECT_TRUE(e->constructor->Is<ast::LiteralExpression>());
+    EXPECT_TRUE(override->constructor->Is<ast::LiteralExpression>());
 
-    auto* id_attr = ast::GetAttribute<ast::IdAttribute>(e.value->attributes);
+    auto* id_attr = ast::GetAttribute<ast::IdAttribute>(override->attributes);
     ASSERT_EQ(id_attr, nullptr);
 }
 
@@ -165,7 +161,8 @@ TEST_F(ParserImplTest, GlobalConstantDec_Override_MissingId) {
     auto e = p->global_constant_decl(attrs.value);
     EXPECT_TRUE(e.matched);
     EXPECT_FALSE(e.errored);
-    ASSERT_NE(e.value, nullptr);
+    auto* override = e.value->As<ast::Override>();
+    ASSERT_NE(override, nullptr);
 
     EXPECT_TRUE(p->has_error());
     EXPECT_EQ(p->error(), "1:5: expected signed integer literal for id attribute");
@@ -180,7 +177,8 @@ TEST_F(ParserImplTest, GlobalConstantDec_Override_InvalidId) {
     auto e = p->global_constant_decl(attrs.value);
     EXPECT_TRUE(e.matched);
     EXPECT_FALSE(e.errored);
-    ASSERT_NE(e.value, nullptr);
+    auto* override = e.value->As<ast::Override>();
+    ASSERT_NE(override, nullptr);
 
     EXPECT_TRUE(p->has_error());
     EXPECT_EQ(p->error(), "1:5: id attribute must be positive");

src/tint/reader/wgsl/parser_impl_global_variable_decl_test.cc

@@ -26,18 +26,19 @@ TEST_F(ParserImplTest, GlobalVariableDecl_WithoutConstructor) {
     ASSERT_FALSE(p->has_error()) << p->error();
     EXPECT_TRUE(e.matched);
     EXPECT_FALSE(e.errored);
-    ASSERT_NE(e.value, nullptr);
+    auto* var = e.value->As<ast::Var>();
+    ASSERT_NE(var, nullptr);
 
-    EXPECT_EQ(e->symbol, p->builder().Symbols().Get("a"));
+    EXPECT_EQ(var->symbol, p->builder().Symbols().Get("a"));
-    EXPECT_TRUE(e->type->Is<ast::F32>());
+    EXPECT_TRUE(var->type->Is<ast::F32>());
-    EXPECT_EQ(e->declared_storage_class, ast::StorageClass::kPrivate);
+    EXPECT_EQ(var->declared_storage_class, ast::StorageClass::kPrivate);
 
-    EXPECT_EQ(e->source.range.begin.line, 1u);
+    EXPECT_EQ(var->source.range.begin.line, 1u);
-    EXPECT_EQ(e->source.range.begin.column, 14u);
+    EXPECT_EQ(var->source.range.begin.column, 14u);
-    EXPECT_EQ(e->source.range.end.line, 1u);
+    EXPECT_EQ(var->source.range.end.line, 1u);
-    EXPECT_EQ(e->source.range.end.column, 15u);
+    EXPECT_EQ(var->source.range.end.column, 15u);
 
-    ASSERT_EQ(e->constructor, nullptr);
+    ASSERT_EQ(var->constructor, nullptr);
 }
 
 TEST_F(ParserImplTest, GlobalVariableDecl_WithConstructor) {
@@ -49,19 +50,20 @@ TEST_F(ParserImplTest, GlobalVariableDecl_WithConstructor) {
     ASSERT_FALSE(p->has_error()) << p->error();
     EXPECT_TRUE(e.matched);
     EXPECT_FALSE(e.errored);
-    ASSERT_NE(e.value, nullptr);
+    auto* var = e.value->As<ast::Var>();
+    ASSERT_NE(var, nullptr);
 
-    EXPECT_EQ(e->symbol, p->builder().Symbols().Get("a"));
+    EXPECT_EQ(var->symbol, p->builder().Symbols().Get("a"));
-    EXPECT_TRUE(e->type->Is<ast::F32>());
+    EXPECT_TRUE(var->type->Is<ast::F32>());
-    EXPECT_EQ(e->declared_storage_class, ast::StorageClass::kPrivate);
+    EXPECT_EQ(var->declared_storage_class, ast::StorageClass::kPrivate);
 
-    EXPECT_EQ(e->source.range.begin.line, 1u);
+    EXPECT_EQ(var->source.range.begin.line, 1u);
-    EXPECT_EQ(e->source.range.begin.column, 14u);
+    EXPECT_EQ(var->source.range.begin.column, 14u);
-    EXPECT_EQ(e->source.range.end.line, 1u);
+    EXPECT_EQ(var->source.range.end.line, 1u);
-    EXPECT_EQ(e->source.range.end.column, 15u);
+    EXPECT_EQ(var->source.range.end.column, 15u);
 
-    ASSERT_NE(e->constructor, nullptr);
+    ASSERT_NE(var->constructor, nullptr);
-    ASSERT_TRUE(e->constructor->Is<ast::FloatLiteralExpression>());
+    ASSERT_TRUE(var->constructor->Is<ast::FloatLiteralExpression>());
 }
 
 TEST_F(ParserImplTest, GlobalVariableDecl_WithAttribute) {
@@ -73,21 +75,22 @@ TEST_F(ParserImplTest, GlobalVariableDecl_WithAttribute) {
     ASSERT_FALSE(p->has_error()) << p->error();
     EXPECT_TRUE(e.matched);
     EXPECT_FALSE(e.errored);
-    ASSERT_NE(e.value, nullptr);
+    auto* var = e.value->As<ast::Var>();
+    ASSERT_NE(var, nullptr);
 
-    EXPECT_EQ(e->symbol, p->builder().Symbols().Get("a"));
+    EXPECT_EQ(var->symbol, p->builder().Symbols().Get("a"));
-    ASSERT_NE(e->type, nullptr);
+    ASSERT_NE(var->type, nullptr);
-    EXPECT_TRUE(e->type->Is<ast::F32>());
+    EXPECT_TRUE(var->type->Is<ast::F32>());
-    EXPECT_EQ(e->declared_storage_class, ast::StorageClass::kUniform);
+    EXPECT_EQ(var->declared_storage_class, ast::StorageClass::kUniform);
 
-    EXPECT_EQ(e->source.range.begin.line, 1u);
+    EXPECT_EQ(var->source.range.begin.line, 1u);
-    EXPECT_EQ(e->source.range.begin.column, 36u);
+    EXPECT_EQ(var->source.range.begin.column, 36u);
-    EXPECT_EQ(e->source.range.end.line, 1u);
+    EXPECT_EQ(var->source.range.end.line, 1u);
-    EXPECT_EQ(e->source.range.end.column, 37u);
+    EXPECT_EQ(var->source.range.end.column, 37u);
 
-    ASSERT_EQ(e->constructor, nullptr);
+    ASSERT_EQ(var->constructor, nullptr);
 
-    auto& attributes = e->attributes;
+    auto& attributes = var->attributes;
     ASSERT_EQ(attributes.size(), 2u);
     ASSERT_TRUE(attributes[0]->Is<ast::BindingAttribute>());
     ASSERT_TRUE(attributes[1]->Is<ast::GroupAttribute>());
@@ -103,21 +106,22 @@ TEST_F(ParserImplTest, GlobalVariableDecl_WithAttribute_MulitpleGroups) {
     ASSERT_FALSE(p->has_error()) << p->error();
     EXPECT_TRUE(e.matched);
     EXPECT_FALSE(e.errored);
-    ASSERT_NE(e.value, nullptr);
+    auto* var = e.value->As<ast::Var>();
+    ASSERT_NE(var, nullptr);
 
-    EXPECT_EQ(e->symbol, p->builder().Symbols().Get("a"));
+    EXPECT_EQ(var->symbol, p->builder().Symbols().Get("a"));
-    ASSERT_NE(e->type, nullptr);
+    ASSERT_NE(var->type, nullptr);
-    EXPECT_TRUE(e->type->Is<ast::F32>());
+    EXPECT_TRUE(var->type->Is<ast::F32>());
-    EXPECT_EQ(e->declared_storage_class, ast::StorageClass::kUniform);
+    EXPECT_EQ(var->declared_storage_class, ast::StorageClass::kUniform);
 
-    EXPECT_EQ(e->source.range.begin.line, 1u);
+    EXPECT_EQ(var->source.range.begin.line, 1u);
-    EXPECT_EQ(e->source.range.begin.column, 36u);
+    EXPECT_EQ(var->source.range.begin.column, 36u);
-    EXPECT_EQ(e->source.range.end.line, 1u);
+    EXPECT_EQ(var->source.range.end.line, 1u);
-    EXPECT_EQ(e->source.range.end.column, 37u);
+    EXPECT_EQ(var->source.range.end.column, 37u);
 
-    ASSERT_EQ(e->constructor, nullptr);
+    ASSERT_EQ(var->constructor, nullptr);
 
-    auto& attributes = e->attributes;
+    auto& attributes = var->attributes;
     ASSERT_EQ(attributes.size(), 2u);
     ASSERT_TRUE(attributes[0]->Is<ast::BindingAttribute>());
     ASSERT_TRUE(attributes[1]->Is<ast::GroupAttribute>());

src/tint/reader/wgsl/parser_impl_param_list_test.cc

@@ -27,7 +27,7 @@ TEST_F(ParserImplTest, ParamList_Single) {
 
     EXPECT_EQ(e.value[0]->symbol, p->builder().Symbols().Get("a"));
     EXPECT_TRUE(e.value[0]->type->Is<ast::I32>());
-    EXPECT_TRUE(e.value[0]->is_const);
+    EXPECT_TRUE(e.value[0]->Is<ast::Parameter>());
 
     ASSERT_EQ(e.value[0]->source.range.begin.line, 1u);
     ASSERT_EQ(e.value[0]->source.range.begin.column, 1u);
@@ -45,7 +45,7 @@ TEST_F(ParserImplTest, ParamList_Multiple) {
 
     EXPECT_EQ(e.value[0]->symbol, p->builder().Symbols().Get("a"));
     EXPECT_TRUE(e.value[0]->type->Is<ast::I32>());
-    EXPECT_TRUE(e.value[0]->is_const);
+    EXPECT_TRUE(e.value[0]->Is<ast::Parameter>());
 
     ASSERT_EQ(e.value[0]->source.range.begin.line, 1u);
     ASSERT_EQ(e.value[0]->source.range.begin.column, 1u);
@@ -54,7 +54,7 @@ TEST_F(ParserImplTest, ParamList_Multiple) {
 
     EXPECT_EQ(e.value[1]->symbol, p->builder().Symbols().Get("b"));
     EXPECT_TRUE(e.value[1]->type->Is<ast::F32>());
-    EXPECT_TRUE(e.value[1]->is_const);
+    EXPECT_TRUE(e.value[1]->Is<ast::Parameter>());
 
     ASSERT_EQ(e.value[1]->source.range.begin.line, 1u);
     ASSERT_EQ(e.value[1]->source.range.begin.column, 10u);
@@ -65,7 +65,7 @@ TEST_F(ParserImplTest, ParamList_Multiple) {
     ASSERT_TRUE(e.value[2]->type->Is<ast::Vector>());
     ASSERT_TRUE(e.value[2]->type->As<ast::Vector>()->type->Is<ast::F32>());
     EXPECT_EQ(e.value[2]->type->As<ast::Vector>()->width, 2u);
-    EXPECT_TRUE(e.value[2]->is_const);
+    EXPECT_TRUE(e.value[2]->Is<ast::Parameter>());
 
     ASSERT_EQ(e.value[2]->source.range.begin.line, 1u);
     ASSERT_EQ(e.value[2]->source.range.begin.column, 18u);
@@ -101,7 +101,7 @@ TEST_F(ParserImplTest, ParamList_Attributes) {
     ASSERT_TRUE(e.value[0]->type->Is<ast::Vector>());
     EXPECT_TRUE(e.value[0]->type->As<ast::Vector>()->type->Is<ast::F32>());
     EXPECT_EQ(e.value[0]->type->As<ast::Vector>()->width, 4u);
-    EXPECT_TRUE(e.value[0]->is_const);
+    EXPECT_TRUE(e.value[0]->Is<ast::Parameter>());
     auto attrs_0 = e.value[0]->attributes;
     ASSERT_EQ(attrs_0.size(), 1u);
     EXPECT_TRUE(attrs_0[0]->Is<ast::BuiltinAttribute>());
@@ -114,7 +114,7 @@ TEST_F(ParserImplTest, ParamList_Attributes) {
 
     EXPECT_EQ(e.value[1]->symbol, p->builder().Symbols().Get("loc1"));
     EXPECT_TRUE(e.value[1]->type->Is<ast::F32>());
-    EXPECT_TRUE(e.value[1]->is_const);
+    EXPECT_TRUE(e.value[1]->Is<ast::Parameter>());
     auto attrs_1 = e.value[1]->attributes;
     ASSERT_EQ(attrs_1.size(), 1u);
     EXPECT_TRUE(attrs_1[0]->Is<ast::LocationAttribute>());

src/tint/resolver/dependency_graph.cc

@@ -487,11 +487,13 @@ struct DependencyAnalysis {
     /// declaration
     std::string KindOf(const ast::Node* node) {
         return Switch(
-            node,  //
+            node,                                              //
-            [&](const ast::Struct*) { return "struct"; },
+            [&](const ast::Struct*) { return "struct"; },      //
-            [&](const ast::Alias*) { return "alias"; },
+            [&](const ast::Alias*) { return "alias"; },        //
-            [&](const ast::Function*) { return "function"; },
+            [&](const ast::Function*) { return "function"; },  //
-            [&](const ast::Variable* var) { return var->is_const ? "let" : "var"; },
+            [&](const ast::Let*) { return "let"; },            //
+            [&](const ast::Var*) { return "var"; },            //
+            [&](const ast::Override*) { return "override"; },  //
             [&](Default) {
                 UnhandledNode(diagnostics_, node);
                 return "<error>";

src/tint/resolver/pipeline_overridable_constant_test.cc

@@ -31,7 +31,7 @@ class ResolverPipelineOverridableConstantTest : public ResolverTest {
         auto* sem = Sem().Get<sem::GlobalVariable>(var);
         ASSERT_NE(sem, nullptr);
         EXPECT_EQ(sem->Declaration(), var);
-        EXPECT_TRUE(sem->IsOverridable());
+        EXPECT_TRUE(sem->Declaration()->Is<ast::Override>());
         EXPECT_EQ(sem->ConstantId(), id);
         EXPECT_FALSE(sem->ConstantValue());
     }
@@ -45,7 +45,7 @@ TEST_F(ResolverPipelineOverridableConstantTest, NonOverridable) {
     auto* sem_a = Sem().Get<sem::GlobalVariable>(a);
     ASSERT_NE(sem_a, nullptr);
     EXPECT_EQ(sem_a->Declaration(), a);
-    EXPECT_FALSE(sem_a->IsOverridable());
+    EXPECT_FALSE(sem_a->Declaration()->Is<ast::Override>());
     EXPECT_TRUE(sem_a->ConstantValue());
 }
 

src/tint/resolver/resolver.cc

@@ -303,59 +303,63 @@ sem::Type* Resolver::Type(const ast::Type* ty) {
     return s;
 }
 
-sem::Variable* Resolver::Variable(const ast::Variable* var,
+sem::Variable* Resolver::Variable(const ast::Variable* v,
-                                  VariableKind kind,
+                                  bool is_global,
                                   uint32_t index /* = 0 */) {
     const sem::Type* storage_ty = nullptr;
 
     // If the variable has a declared type, resolve it.
-    if (auto* ty = var->type) {
+    if (auto* ty = v->type) {
         storage_ty = Type(ty);
         if (!storage_ty) {
             return nullptr;
         }
     }
 
+    auto* as_var = v->As<ast::Var>();
+    auto* as_let = v->As<ast::Let>();
+    auto* as_override = v->As<ast::Override>();
+    auto* as_param = v->As<ast::Parameter>();
+
     const sem::Expression* rhs = nullptr;
 
     // Does the variable have a constructor?
-    if (var->constructor) {
+    if (v->constructor) {
-        rhs = Materialize(Expression(var->constructor), storage_ty);
+        rhs = Materialize(Expression(v->constructor), storage_ty);
         if (!rhs) {
             return nullptr;
         }
 
         // If the variable has no declared type, infer it from the RHS
         if (!storage_ty) {
-            if (!var->is_const && kind == VariableKind::kGlobal) {
+            if (as_var && is_global) {
-                AddError("module-scope 'var' declaration must specify a type", var->source);
+                AddError("module-scope 'var' declaration must specify a type", v->source);
                 return nullptr;
             }
 
             storage_ty = rhs->Type()->UnwrapRef();  // Implicit load of RHS
         }
-    } else if (var->is_const && !var->is_overridable && kind != VariableKind::kParameter) {
+    } else if (as_let) {
-        AddError("'let' declaration must have an initializer", var->source);
+        AddError("'let' declaration must have an initializer", v->source);
         return nullptr;
-    } else if (!var->type) {
+    } else if (!v->type) {
-        AddError((kind == VariableKind::kGlobal)
+        AddError((is_global) ? "module-scope 'var' declaration requires a type or initializer"
-                     ? "module-scope 'var' declaration requires a type or initializer"
+                             : "function-scope 'var' declaration requires a type or initializer",
-                     : "function-scope 'var' declaration requires a type or initializer",
+                 v->source);
-                 var->source);
         return nullptr;
     }
 
     if (!storage_ty) {
         TINT_ICE(Resolver, diagnostics_) << "failed to determine storage type for variable '" +
-                                                builder_->Symbols().NameFor(var->symbol) + "'\n"
+                                                builder_->Symbols().NameFor(v->symbol) + "'\n"
-                                         << "Source: " << var->source;
+                                         << "Source: " << v->source;
         return nullptr;
     }
 
-    auto storage_class = var->declared_storage_class;
+    auto storage_class = as_var ? as_var->declared_storage_class : ast::StorageClass::kNone;
-    if (storage_class == ast::StorageClass::kNone && !var->is_const) {
+    if (storage_class == ast::StorageClass::kNone && as_var) {
         // No declared storage class. Infer from usage / type.
-        if (kind == VariableKind::kLocal) {
+        if (!is_global) {
             storage_class = ast::StorageClass::kFunction;
         } else if (storage_ty->UnwrapRef()->is_handle()) {
             // https://gpuweb.github.io/gpuweb/wgsl/#module-scope-variables
@@ -366,93 +370,83 @@ sem::Variable* Resolver::Variable(const ast::Variable* var,
         }
     }
 
-    if (kind == VariableKind::kLocal && !var->is_const &&
+    if (!is_global && as_var && storage_class != ast::StorageClass::kFunction &&
-        storage_class != ast::StorageClass::kFunction &&
+        validator_.IsValidationEnabled(v->attributes,
-        validator_.IsValidationEnabled(var->attributes,
                                        ast::DisabledValidation::kIgnoreStorageClass)) {
-        AddError("function-scope 'var' declaration must use 'function' storage class", var->source);
+        AddError("function-scope 'var' declaration must use 'function' storage class", v->source);
         return nullptr;
     }
 
-    auto access = var->declared_access;
+    auto access = as_var ? as_var->declared_access : ast::Access::kUndefined;
     if (access == ast::Access::kUndefined) {
         access = DefaultAccessForStorageClass(storage_class);
     }
 
     auto* var_ty = storage_ty;
-    if (!var->is_const) {
+    if (as_var) {
-        // Variable declaration. Unlike `let`, `var` has storage.
+        // Variable declaration. Unlike `let` and parameters, `var` has storage.
         // Variables are always of a reference type to the declared storage type.
         var_ty = builder_->create<sem::Reference>(storage_ty, storage_class, access);
     }
 
-    if (rhs && !validator_.VariableConstructorOrCast(var, storage_class, storage_ty, rhs->Type())) {
+    if (rhs && !validator_.VariableConstructorOrCast(v, storage_class, storage_ty, rhs->Type())) {
         return nullptr;
     }
 
-    if (!ApplyStorageClassUsageToType(storage_class, const_cast<sem::Type*>(var_ty), var->source)) {
+    if (!ApplyStorageClassUsageToType(storage_class, const_cast<sem::Type*>(var_ty), v->source)) {
-        AddNote(std::string("while instantiating ") +
+        AddNote(std::string("while instantiating ") + ((as_param) ? "parameter " : "variable ") +
-                    ((kind == VariableKind::kParameter) ? "parameter " : "variable ") +
+                    builder_->Symbols().NameFor(v->symbol),
-                    builder_->Symbols().NameFor(var->symbol),
+                v->source);
-                var->source);
         return nullptr;
     }
 
-    if (kind == VariableKind::kParameter) {
+    if (as_param) {
         if (auto* ptr = var_ty->As<sem::Pointer>()) {
             // For MSL, we push module-scope variables into the entry point as pointer
             // parameters, so we also need to handle their store type.
             if (!ApplyStorageClassUsageToType(
-                    ptr->StorageClass(), const_cast<sem::Type*>(ptr->StoreType()), var->source)) {
+                    ptr->StorageClass(), const_cast<sem::Type*>(ptr->StoreType()), v->source)) {
-                AddNote("while instantiating parameter " + builder_->Symbols().NameFor(var->symbol),
+                AddNote("while instantiating parameter " + builder_->Symbols().NameFor(v->symbol),
-                        var->source);
+                        v->source);
                 return nullptr;
             }
         }
+        auto* param =
+            builder_->create<sem::Parameter>(as_param, index, var_ty, storage_class, access);
+        builder_->Sem().Add(as_param, param);
+        return param;
     }
 
-    switch (kind) {
+    if (is_global) {
-        case VariableKind::kGlobal: {
+        sem::BindingPoint binding_point;
-            sem::BindingPoint binding_point;
+        if (as_var) {
-            if (auto bp = var->BindingPoint()) {
+            if (auto bp = as_var->BindingPoint()) {
                 binding_point = {bp.group->value, bp.binding->value};
             }
+        }
 
-            bool has_const_val = rhs && var->is_const && !var->is_overridable;
+        bool has_const_val = rhs && as_let && !as_override;
-            auto* global = builder_->create<sem::GlobalVariable>(
+        auto* global = builder_->create<sem::GlobalVariable>(
-                var, var_ty, storage_class, access,
+            v, var_ty, storage_class, access,
-                has_const_val ? rhs->ConstantValue() : sem::Constant{}, binding_point);
+            has_const_val ? rhs->ConstantValue() : sem::Constant{}, binding_point);
 
-            if (var->is_overridable) {
+        if (as_override) {
-                global->SetIsOverridable();
+            if (auto* id = ast::GetAttribute<ast::IdAttribute>(v->attributes)) {
-                if (auto* id = ast::GetAttribute<ast::IdAttribute>(var->attributes)) {
+                global->SetConstantId(static_cast<uint16_t>(id->value));
-                    global->SetConstantId(static_cast<uint16_t>(id->value));
-                }
             }
+        }
 
-            global->SetConstructor(rhs);
+        global->SetConstructor(rhs);
-
+        builder_->Sem().Add(v, global);
-            builder_->Sem().Add(var, global);
+        return global;
-            return global;
-        }
-        case VariableKind::kLocal: {
-            auto* local = builder_->create<sem::LocalVariable>(
-                var, var_ty, storage_class, access, current_statement_,
-                (rhs && var->is_const) ? rhs->ConstantValue() : sem::Constant{});
-            builder_->Sem().Add(var, local);
-            local->SetConstructor(rhs);
-            return local;
-        }
-        case VariableKind::kParameter: {
-            auto* param =
-                builder_->create<sem::Parameter>(var, index, var_ty, storage_class, access);
-            builder_->Sem().Add(var, param);
-            return param;
-        }
     }
 
-    TINT_UNREACHABLE(Resolver, diagnostics_) << "unhandled VariableKind " << static_cast<int>(kind);
+    auto* local = builder_->create<sem::LocalVariable>(
-    return nullptr;
+        v, var_ty, storage_class, access, current_statement_,
+        (rhs && as_let) ? rhs->ConstantValue() : sem::Constant{});
+    builder_->Sem().Add(v, local);
+    local->SetConstructor(rhs);
+    return local;
 }
 
 ast::Access Resolver::DefaultAccessForStorageClass(ast::StorageClass storage_class) {
@@ -477,13 +471,13 @@ void Resolver::AllocateOverridableConstantIds() {
     // TODO(crbug.com/tint/1192): If a transform changes the order or removes an
     // unused constant, the allocation may change on the next Resolver pass.
     for (auto* decl : builder_->AST().GlobalDeclarations()) {
-        auto* var = decl->As<ast::Variable>();
+        auto* override = decl->As<ast::Override>();
-        if (!var || !var->is_overridable) {
+        if (!override) {
             continue;
         }
 
         uint16_t constant_id;
-        if (auto* id_attr = ast::GetAttribute<ast::IdAttribute>(var->attributes)) {
+        if (auto* id_attr = ast::GetAttribute<ast::IdAttribute>(override->attributes)) {
             constant_id = static_cast<uint16_t>(id_attr->value);
         } else {
             // No ID was specified, so allocate the next available ID.
@@ -499,7 +493,7 @@ void Resolver::AllocateOverridableConstantIds() {
             next_constant_id = constant_id + 1;
         }
 
-        auto* sem = sem_.Get<sem::GlobalVariable>(var);
+        auto* sem = sem_.Get<sem::GlobalVariable>(override);
         const_cast<sem::GlobalVariable*>(sem)->SetConstantId(constant_id);
     }
 }
@@ -513,25 +507,21 @@ void Resolver::SetShadows() {
     }
 }
 
-sem::GlobalVariable* Resolver::GlobalVariable(const ast::Variable* var) {
+sem::GlobalVariable* Resolver::GlobalVariable(const ast::Variable* v) {
-    auto* sem = Variable(var, VariableKind::kGlobal);
+    auto* sem = As<sem::GlobalVariable>(Variable(v, /* is_global */ true));
     if (!sem) {
         return nullptr;
     }
 
+    const bool is_var = v->Is<ast::Var>();
+
     auto storage_class = sem->StorageClass();
-    if (!var->is_const && storage_class == ast::StorageClass::kNone) {
+    if (is_var && storage_class == ast::StorageClass::kNone) {
-        AddError("module-scope 'var' declaration must have a storage class", var->source);
+        AddError("module-scope 'var' declaration must have a storage class", v->source);
-        return nullptr;
-    }
-    if (var->is_const && storage_class != ast::StorageClass::kNone) {
-        AddError(var->is_overridable ? "'override' declaration must not have a storage class"
-                                     : "'let' declaration must not have a storage class",
-                 var->source);
         return nullptr;
     }
 
-    for (auto* attr : var->attributes) {
+    for (auto* attr : v->attributes) {
         Mark(attr);
 
         if (auto* id_attr = attr->As<ast::IdAttribute>()) {
@@ -540,7 +530,7 @@ sem::GlobalVariable* Resolver::GlobalVariable(const ast::Variable* var) {
         }
     }
 
-    if (!validator_.NoDuplicateAttributes(var->attributes)) {
+    if (!validator_.NoDuplicateAttributes(v->attributes)) {
         return nullptr;
     }
 
@@ -576,9 +566,8 @@ sem::Function* Resolver::Function(const ast::Function* decl) {
             }
         }
 
-        auto* var =
+        auto* p = As<sem::Parameter>(Variable(param, false, parameter_index++));
-            As<sem::Parameter>(Variable(param, VariableKind::kParameter, parameter_index++));
+        if (!p) {
-        if (!var) {
             return nullptr;
         }
 
@@ -589,10 +578,10 @@ sem::Function* Resolver::Function(const ast::Function* decl) {
             return nullptr;
         }
 
-        parameters.emplace_back(var);
+        parameters.emplace_back(p);
 
-        auto* var_ty = const_cast<sem::Type*>(var->Type());
+        auto* p_ty = const_cast<sem::Type*>(p->Type());
-        if (auto* str = var_ty->As<sem::Struct>()) {
+        if (auto* str = p_ty->As<sem::Struct>()) {
             switch (decl->PipelineStage()) {
                 case ast::PipelineStage::kVertex:
                     str->AddUsage(sem::PipelineStageUsage::kVertexInput);
@@ -777,12 +766,12 @@ bool Resolver::WorkgroupSize(const ast::Function* func) {
         if (auto* user = args[i]->As<sem::VariableUser>()) {
             // We have an variable of a module-scope constant.
             auto* decl = user->Variable()->Declaration();
-            if (!decl->is_const) {
+            if (!decl->IsAnyOf<ast::Let, ast::Override>()) {
                 AddError(kErrBadType, values[i]->source);
                 return false;
             }
             // Capture the constant if it is pipeline-overridable.
-            if (decl->is_overridable) {
+            if (decl->Is<ast::Override>()) {
                 ws[i].overridable_const = decl;
             }
 
@@ -2104,19 +2093,19 @@ sem::Array* Resolver::Array(const ast::Array* arr) {
             return nullptr;
         }
 
+        constexpr const char* kErrInvalidExpr =
+            "array size identifier must be a literal or a module-scope 'let'";
+
         if (auto* ident = count_expr->As<ast::IdentifierExpression>()) {
-            // Make sure the identifier is a non-overridable module-scope constant.
+            // Make sure the identifier is a non-overridable module-scope 'let'.
-            auto* var = sem_.ResolvedSymbol<sem::GlobalVariable>(ident);
+            auto* global = sem_.ResolvedSymbol<sem::GlobalVariable>(ident);
-            if (!var || !var->Declaration()->is_const || var->IsOverridable()) {
+            if (!global || !global->Declaration()->Is<ast::Let>()) {
-                AddError("array size identifier must be a literal or a module-scope 'let'",
+                AddError(kErrInvalidExpr, size_source);
-                         size_source);
                 return nullptr;
             }
-
+            count_expr = global->Declaration()->constructor;
-            count_expr = var->Declaration()->constructor;
         } else if (!count_expr->Is<ast::LiteralExpression>()) {
-            AddError("array size identifier must be a literal or a module-scope 'let'",
+            AddError(kErrInvalidExpr, size_source);
-                     size_source);
             return nullptr;
         }
 
@@ -2437,7 +2426,7 @@ sem::Statement* Resolver::VariableDeclStatement(const ast::VariableDeclStatement
     return StatementScope(stmt, sem, [&] {
         Mark(stmt->variable);
 
-        auto* var = Variable(stmt->variable, VariableKind::kLocal);
+        auto* var = Variable(stmt->variable, /* is_global */ false);
         if (!var) {
             return false;
         }

src/tint/resolver/resolver.h

@@ -109,9 +109,6 @@ class Resolver {
     const Validator* GetValidatorForTesting() const { return &validator_; }
 
   private:
-    /// Describes the context in which a variable is declared
-    enum class VariableKind { kParameter, kLocal, kGlobal };
-
     Validator::ValidTypeStorageLayouts valid_type_storage_layouts_;
 
     /// Structure holding semantic information about a block (i.e. scope), such as
@@ -298,9 +295,9 @@ class Resolver {
     /// @note this method does not resolve the attributes as these are
     /// context-dependent (global, local, parameter)
     /// @param var the variable to create or return the `VariableInfo` for
-    /// @param kind what kind of variable we are declaring
+    /// @param is_global true if this is module scope, otherwise function scope
     /// @param index the index of the parameter, if this variable is a parameter
-    sem::Variable* Variable(const ast::Variable* var, VariableKind kind, uint32_t index = 0);
+    sem::Variable* Variable(const ast::Variable* var, bool is_global, uint32_t index = 0);
 
     /// Records the storage class usage for the given type, and any transient
     /// dependencies of the type. Validates that the type can be used for the

src/tint/resolver/type_validation_test.cc

@@ -87,26 +87,6 @@ TEST_F(ResolverTypeValidationTest, GlobalVariableWithStorageClass_Pass) {
     EXPECT_TRUE(r()->Resolve()) << r()->error();
 }
 
-TEST_F(ResolverTypeValidationTest, GlobalLetWithStorageClass_Fail) {
-    // let<private> global_var: f32;
-    AST().AddGlobalVariable(create<ast::Variable>(
-        Source{{12, 34}}, Symbols().Register("global_let"), ast::StorageClass::kPrivate,
-        ast::Access::kUndefined, ty.f32(), true, false, Expr(1.23_f), ast::AttributeList{}));
-
-    EXPECT_FALSE(r()->Resolve());
-    EXPECT_EQ(r()->error(), "12:34 error: 'let' declaration must not have a storage class");
-}
-
-TEST_F(ResolverTypeValidationTest, OverrideWithStorageClass_Fail) {
-    // let<private> global_var: f32;
-    AST().AddGlobalVariable(create<ast::Variable>(
-        Source{{12, 34}}, Symbols().Register("global_override"), ast::StorageClass::kPrivate,
-        ast::Access::kUndefined, ty.f32(), true, true, Expr(1.23_f), ast::AttributeList{}));
-
-    EXPECT_FALSE(r()->Resolve());
-    EXPECT_EQ(r()->error(), "12:34 error: 'override' declaration must not have a storage class");
-}
-
 TEST_F(ResolverTypeValidationTest, GlobalConstNoStorageClass_Pass) {
     // let global_var: f32;
     GlobalConst(Source{{12, 34}}, "global_var", ty.f32(), Construct(ty.f32()));

src/tint/resolver/uniformity.cc

@@ -949,7 +949,7 @@ class UniformityGraph {
                 }
                 current_function_->variables.Set(sem_.Get(decl->variable), node);
 
-                if (!decl->variable->is_const) {
+                if (decl->variable->Is<ast::Var>()) {
                     current_function_->local_var_decls.insert(
                         sem_.Get<sem::LocalVariable>(decl->variable));
                 }
@@ -1018,7 +1018,8 @@ class UniformityGraph {
             },
 
             [&](const sem::GlobalVariable* global) {
-                if (global->Declaration()->is_const || global->Access() == ast::Access::kRead) {
+                if (!global->Declaration()->Is<ast::Var>() ||
+                    global->Access() == ast::Access::kRead) {
                     node->AddEdge(cf);
                 } else {
                     node->AddEdge(current_function_->may_be_non_uniform);

src/tint/resolver/validator.cc

@@ -297,7 +297,7 @@ bool Validator::Materialize(const sem::Materialize* m) const {
     return true;
 }
 
-bool Validator::VariableConstructorOrCast(const ast::Variable* var,
+bool Validator::VariableConstructorOrCast(const ast::Variable* v,
                                           ast::StorageClass storage_class,
                                           const sem::Type* storage_ty,
                                           const sem::Type* rhs_ty) const {
@@ -305,14 +305,14 @@ bool Validator::VariableConstructorOrCast(const ast::Variable* var,
 
     // Value type has to match storage type
     if (storage_ty != value_type) {
-        std::string decl = var->is_const ? "let" : "var";
+        std::string decl = v->Is<ast::Let>() ? "let" : "var";
         AddError("cannot initialize " + decl + " of type '" + sem_.TypeNameOf(storage_ty) +
                      "' with value of type '" + sem_.TypeNameOf(rhs_ty) + "'",
-                 var->source);
+                 v->source);
         return false;
     }
 
-    if (!var->is_const) {
+    if (v->Is<ast::Var>()) {
         switch (storage_class) {
             case ast::StorageClass::kPrivate:
             case ast::StorageClass::kFunction:
@@ -325,7 +325,7 @@ bool Validator::VariableConstructorOrCast(const ast::Variable* var,
                              "' cannot have an initializer. var initializers are only "
                              "supported for the storage classes "
                              "'private' and 'function'",
-                         var->source);
+                         v->source);
                 return false;
         }
     }
@@ -502,21 +502,22 @@ bool Validator::StorageClassLayout(const sem::Variable* var,
 }
 
 bool Validator::GlobalVariable(
-    const sem::Variable* var,
+    const sem::GlobalVariable* global,
     std::unordered_map<uint32_t, const sem::Variable*> constant_ids,
     std::unordered_map<const sem::Type*, const Source&> atomic_composite_info) const {
-    auto* decl = var->Declaration();
+    auto* decl = global->Declaration();
     if (!NoDuplicateAttributes(decl->attributes)) {
         return false;
     }
 
-    for (auto* attr : decl->attributes) {
+    bool ok = Switch(
-        if (decl->is_const) {
+        decl,  //
-            if (decl->is_overridable) {
+        [&](const ast::Override*) {
+            for (auto* attr : decl->attributes) {
                 if (auto* id_attr = attr->As<ast::IdAttribute>()) {
                     uint32_t id = id_attr->value;
                     auto it = constant_ids.find(id);
-                    if (it != constant_ids.end() && it->second != var) {
+                    if (it != constant_ids.end() && it->second != global) {
                         AddError("pipeline constant IDs must be unique", attr->source);
                         AddNote("a pipeline constant with an ID of " + std::to_string(id) +
                                     " was previously declared here:",
@@ -533,32 +534,45 @@ bool Validator::GlobalVariable(
                     AddError("attribute is not valid for 'override' declaration", attr->source);
                     return false;
                 }
-            } else {
+            }
-                AddError("attribute is not valid for module-scope 'let' declaration", attr->source);
+            return true;
+        },
+        [&](const ast::Let*) {
+            if (!decl->attributes.empty()) {
+                AddError("attribute is not valid for module-scope 'let' declaration",
+                         decl->attributes[0]->source);
                 return false;
             }
-        } else {
+            return true;
-            bool is_shader_io_attribute =
+        },
-                attr->IsAnyOf<ast::BuiltinAttribute, ast::InterpolateAttribute,
+        [&](const ast::Var*) {
-                              ast::InvariantAttribute, ast::LocationAttribute>();
+            for (auto* attr : decl->attributes) {
-            bool has_io_storage_class = var->StorageClass() == ast::StorageClass::kInput ||
+                bool is_shader_io_attribute =
-                                        var->StorageClass() == ast::StorageClass::kOutput;
+                    attr->IsAnyOf<ast::BuiltinAttribute, ast::InterpolateAttribute,
-            if (!(attr->IsAnyOf<ast::BindingAttribute, ast::GroupAttribute,
+                                  ast::InvariantAttribute, ast::LocationAttribute>();
-                                ast::InternalAttribute>()) &&
+                bool has_io_storage_class = global->StorageClass() == ast::StorageClass::kInput ||
-                (!is_shader_io_attribute || !has_io_storage_class)) {
+                                            global->StorageClass() == ast::StorageClass::kOutput;
-                AddError("attribute is not valid for module-scope 'var'", attr->source);
+                if (!attr->IsAnyOf<ast::BindingAttribute, ast::GroupAttribute,
-                return false;
+                                   ast::InternalAttribute>() &&
+                    (!is_shader_io_attribute || !has_io_storage_class)) {
+                    AddError("attribute is not valid for module-scope 'var'", attr->source);
+                    return false;
+                }
             }
-        }
+            return true;
+        });
+
+    if (!ok) {
+        return false;
     }
 
-    if (var->StorageClass() == ast::StorageClass::kFunction) {
+    if (global->StorageClass() == ast::StorageClass::kFunction) {
         AddError("module-scope 'var' must not use storage class 'function'", decl->source);
         return false;
     }
 
     auto binding_point = decl->BindingPoint();
-    switch (var->StorageClass()) {
+    switch (global->StorageClass()) {
         case ast::StorageClass::kUniform:
         case ast::StorageClass::kStorage:
         case ast::StorageClass::kHandle: {
@@ -581,23 +595,23 @@ bool Validator::GlobalVariable(
             }
     }
 
-    // https://gpuweb.github.io/gpuweb/wgsl/#variable-declaration
+    if (auto* var = decl->As<ast::Var>()) {
-    // The access mode always has a default, and except for variables in the
+        // https://gpuweb.github.io/gpuweb/wgsl/#variable-declaration
-    // storage storage class, must not be written.
+        // The access mode always has a default, and except for variables in the
-    if (var->StorageClass() != ast::StorageClass::kStorage &&
+        // storage storage class, must not be written.
-        decl->declared_access != ast::Access::kUndefined) {
+        if (global->StorageClass() != ast::StorageClass::kStorage &&
-        AddError("only variables in <storage> storage class may declare an access mode",
+            var->declared_access != ast::Access::kUndefined) {
-                 decl->source);
+            AddError("only variables in <storage> storage class may declare an access mode",
-        return false;
+                     var->source);
-    }
+            return false;
+        }
 
-    if (!decl->is_const) {
+        if (!AtomicVariable(global, atomic_composite_info)) {
-        if (!AtomicVariable(var, atomic_composite_info)) {
             return false;
         }
     }
 
-    return Variable(var);
+    return Variable(global);
 }
 
 // https://gpuweb.github.io/gpuweb/wgsl/#atomic-types
@@ -641,14 +655,17 @@ bool Validator::AtomicVariable(
     return true;
 }
 
-bool Validator::Variable(const sem::Variable* var) const {
+bool Validator::Variable(const sem::Variable* v) const {
-    auto* decl = var->Declaration();
+    auto* decl = v->Declaration();
-    auto* storage_ty = var->Type()->UnwrapRef();
+    auto* storage_ty = v->Type()->UnwrapRef();
 
-    if (var->Is<sem::GlobalVariable>()) {
+    auto* as_let = decl->As<ast::Let>();
+    auto* as_var = decl->As<ast::Var>();
+
+    if (v->Is<sem::GlobalVariable>()) {
         auto name = symbols_.NameFor(decl->symbol);
         if (sem::ParseBuiltinType(name) != sem::BuiltinType::kNone) {
-            auto* kind = var->Declaration()->is_const ? "let" : "var";
+            auto* kind = as_let ? "let" : "var";
             AddError(
                 "'" + name + "' is a builtin and cannot be redeclared as a module-scope " + kind,
                 decl->source);
@@ -656,14 +673,13 @@ bool Validator::Variable(const sem::Variable* var) const {
         }
     }
 
-    if (!decl->is_const && !IsStorable(storage_ty)) {
+    if (as_var && !IsStorable(storage_ty)) {
         AddError(sem_.TypeNameOf(storage_ty) + " cannot be used as the type of a var",
                  decl->source);
         return false;
     }
 
-    if (decl->is_const && !var->Is<sem::Parameter>() &&
+    if (as_let && !(storage_ty->IsConstructible() || storage_ty->Is<sem::Pointer>())) {
-        !(storage_ty->IsConstructible() || storage_ty->Is<sem::Pointer>())) {
         AddError(sem_.TypeNameOf(storage_ty) + " cannot be used as the type of a let",
                  decl->source);
         return false;
@@ -688,16 +704,17 @@ bool Validator::Variable(const sem::Variable* var) const {
         }
     }
 
-    if (var->Is<sem::LocalVariable>() && !decl->is_const &&
+    if (v->Is<sem::LocalVariable>() && as_var &&
         IsValidationEnabled(decl->attributes, ast::DisabledValidation::kIgnoreStorageClass)) {
-        if (!var->Type()->UnwrapRef()->IsConstructible()) {
+        if (!v->Type()->UnwrapRef()->IsConstructible()) {
             AddError("function variable must have a constructible type",
                      decl->type ? decl->type->source : decl->source);
             return false;
         }
     }
 
-    if (storage_ty->is_handle() && decl->declared_storage_class != ast::StorageClass::kNone) {
+    if (as_var && storage_ty->is_handle() &&
+        as_var->declared_storage_class != ast::StorageClass::kNone) {
         // https://gpuweb.github.io/gpuweb/wgsl/#module-scope-variables
         // If the store type is a texture type or a sampler type, then the
         // variable declaration must not have a storage class attribute. The
@@ -709,9 +726,10 @@ bool Validator::Variable(const sem::Variable* var) const {
     }
 
     if (IsValidationEnabled(decl->attributes, ast::DisabledValidation::kIgnoreStorageClass) &&
-        (decl->declared_storage_class == ast::StorageClass::kInput ||
+        as_var &&
-         decl->declared_storage_class == ast::StorageClass::kOutput)) {
+        (as_var->declared_storage_class == ast::StorageClass::kInput ||
-        AddError("invalid use of input/output storage class", decl->source);
+         as_var->declared_storage_class == ast::StorageClass::kOutput)) {
+        AddError("invalid use of input/output storage class", as_var->source);
         return false;
     }
     return true;
@@ -1223,12 +1241,12 @@ bool Validator::EntryPoint(const sem::Function* func, ast::PipelineStage stage)
 
     // Validate there are no resource variable binding collisions
     std::unordered_map<sem::BindingPoint, const ast::Variable*> binding_points;
-    for (auto* var : func->TransitivelyReferencedGlobals()) {
+    for (auto* global : func->TransitivelyReferencedGlobals()) {
-        auto* var_decl = var->Declaration();
+        auto* var_decl = global->Declaration()->As<ast::Var>();
-        if (!var_decl->BindingPoint()) {
+        if (!var_decl || !var_decl->BindingPoint()) {
             continue;
         }
-        auto bp = var->BindingPoint();
+        auto bp = global->BindingPoint();
         auto res = binding_points.emplace(bp, var_decl);
         if (!res.second &&
             IsValidationEnabled(decl->attributes,
@@ -1663,12 +1681,6 @@ bool Validator::FunctionCall(const sem::Call* call, sem::Statement* current_stat
                             TINT_ICE(Resolver, diagnostics_) << "failed to resolve identifier";
                             return false;
                         }
-                        if (var->Declaration()->is_const) {
-                            TINT_ICE(Resolver, diagnostics_)
-                                << "Resolver::FunctionCall() encountered an address-of "
-                                   "expression of a constant identifier expression";
-                            return false;
-                        }
                         is_valid = true;
                     }
                 }
@@ -2172,18 +2184,16 @@ bool Validator::Assignment(const ast::Statement* a, const sem::Type* rhs_ty) con
     // https://gpuweb.github.io/gpuweb/wgsl/#assignment-statement
     auto const* lhs_ty = sem_.TypeOf(lhs);
 
-    if (auto* var = sem_.ResolvedSymbol<sem::Variable>(lhs)) {
+    if (auto* variable = sem_.ResolvedSymbol<sem::Variable>(lhs)) {
-        auto* decl = var->Declaration();
+        auto* v = variable->Declaration();
-        if (var->Is<sem::Parameter>()) {
+        const char* err = Switch(
-            AddError("cannot assign to function parameter", lhs->source);
+            v,  //
-            AddNote("'" + symbols_.NameFor(decl->symbol) + "' is declared here:", decl->source);
+            [&](const ast::Parameter*) { return "cannot assign to function parameter"; },
-            return false;
+            [&](const ast::Let*) { return "cannot assign to 'let'"; },
-        }
+            [&](const ast::Override*) { return "cannot assign to 'override'"; });
-        if (decl->is_const) {
+        if (err) {
-            AddError(
+            AddError(err, lhs->source);
-                decl->is_overridable ? "cannot assign to 'override'" : "cannot assign to 'let'",
+            AddNote("'" + symbols_.NameFor(v->symbol) + "' is declared here:", v->source);
-                lhs->source);
-            AddNote("'" + symbols_.NameFor(decl->symbol) + "' is declared here:", decl->source);
             return false;
         }
     }
@@ -2222,17 +2232,16 @@ bool Validator::IncrementDecrementStatement(const ast::IncrementDecrementStateme
 
     // https://gpuweb.github.io/gpuweb/wgsl/#increment-decrement
 
-    if (auto* var = sem_.ResolvedSymbol<sem::Variable>(lhs)) {
+    if (auto* variable = sem_.ResolvedSymbol<sem::Variable>(lhs)) {
-        auto* decl = var->Declaration();
+        auto* v = variable->Declaration();
-        if (var->Is<sem::Parameter>()) {
+        const char* err = Switch(
-            AddError("cannot modify function parameter", lhs->source);
+            v,  //
-            AddNote("'" + symbols_.NameFor(decl->symbol) + "' is declared here:", decl->source);
+            [&](const ast::Parameter*) { return "cannot modify function parameter"; },
-            return false;
+            [&](const ast::Let*) { return "cannot modify 'let'"; },
-        }
+            [&](const ast::Override*) { return "cannot modify 'override'"; });
-        if (decl->is_const) {
+        if (err) {
-            AddError(decl->is_overridable ? "cannot modify 'override'" : "cannot modify 'let'",
+            AddError(err, lhs->source);
-                     lhs->source);
+            AddNote("'" + symbols_.NameFor(v->symbol) + "' is declared here:", v->source);
-            AddNote("'" + symbols_.NameFor(decl->symbol) + "' is declared here:", decl->source);
             return false;
         }
     }

src/tint/resolver/validator.h

@@ -237,7 +237,7 @@ class Validator {
     /// @param atomic_composite_info atomic composite info in the module
     /// @returns true on success, false otherwise
     bool GlobalVariable(
-        const sem::Variable* var,
+        const sem::GlobalVariable* var,
         std::unordered_map<uint32_t, const sem::Variable*> constant_ids,
         std::unordered_map<const sem::Type*, const Source&> atomic_composite_info) const;
 
@@ -345,12 +345,12 @@ class Validator {
     bool Variable(const sem::Variable* var) const;
 
     /// Validates a variable constructor or cast
-    /// @param var the variable to validate
+    /// @param v the variable to validate
     /// @param storage_class the storage class of the variable
     /// @param storage_type the type of the storage
     /// @param rhs_type the right hand side of the expression
     /// @returns true on succes, false otherwise
-    bool VariableConstructorOrCast(const ast::Variable* var,
+    bool VariableConstructorOrCast(const ast::Variable* v,
                                    ast::StorageClass storage_class,
                                    const sem::Type* storage_type,
                                    const sem::Type* rhs_type) const;

src/tint/resolver/var_let_validation_test.cc

@@ -24,22 +24,6 @@ namespace {
 
 struct ResolverVarLetValidationTest : public resolver::TestHelper, public testing::Test {};
 
-TEST_F(ResolverVarLetValidationTest, LetNoInitializer) {
-    // let a : i32;
-    WrapInFunction(Let(Source{{12, 34}}, "a", ty.i32(), nullptr));
-
-    EXPECT_FALSE(r()->Resolve());
-    EXPECT_EQ(r()->error(), "12:34 error: 'let' declaration must have an initializer");
-}
-
-TEST_F(ResolverVarLetValidationTest, GlobalLetNoInitializer) {
-    // let a : i32;
-    GlobalConst(Source{{12, 34}}, "a", ty.i32(), nullptr);
-
-    EXPECT_FALSE(r()->Resolve());
-    EXPECT_EQ(r()->error(), "12:34 error: 'let' declaration must have an initializer");
-}
-
 TEST_F(ResolverVarLetValidationTest, VarNoInitializerNoType) {
     // var a;
     WrapInFunction(Var(Source{{12, 34}}, "a", nullptr));

src/tint/sem/function.cc

@@ -44,10 +44,10 @@ std::vector<std::pair<const Variable*, const ast::LocationAttribute*>>
 Function::TransitivelyReferencedLocationVariables() const {
     std::vector<std::pair<const Variable*, const ast::LocationAttribute*>> ret;
 
-    for (auto* var : TransitivelyReferencedGlobals()) {
+    for (auto* global : TransitivelyReferencedGlobals()) {
-        for (auto* attr : var->Declaration()->attributes) {
+        for (auto* attr : global->Declaration()->attributes) {
             if (auto* location = attr->As<ast::LocationAttribute>()) {
-                ret.push_back({var, location});
+                ret.push_back({global, location});
                 break;
             }
         }
@@ -58,13 +58,13 @@ Function::TransitivelyReferencedLocationVariables() const {
 Function::VariableBindings Function::TransitivelyReferencedUniformVariables() const {
     VariableBindings ret;
 
-    for (auto* var : TransitivelyReferencedGlobals()) {
+    for (auto* global : TransitivelyReferencedGlobals()) {
-        if (var->StorageClass() != ast::StorageClass::kUniform) {
+        if (global->StorageClass() != ast::StorageClass::kUniform) {
             continue;
         }
 
-        if (auto binding_point = var->Declaration()->BindingPoint()) {
+        if (auto binding_point = global->Declaration()->BindingPoint()) {
-            ret.push_back({var, binding_point});
+            ret.push_back({global, binding_point});
         }
     }
     return ret;
@@ -73,13 +73,13 @@ Function::VariableBindings Function::TransitivelyReferencedUniformVariables() co
 Function::VariableBindings Function::TransitivelyReferencedStorageBufferVariables() const {
     VariableBindings ret;
 
-    for (auto* var : TransitivelyReferencedGlobals()) {
+    for (auto* global : TransitivelyReferencedGlobals()) {
-        if (var->StorageClass() != ast::StorageClass::kStorage) {
+        if (global->StorageClass() != ast::StorageClass::kStorage) {
             continue;
         }
 
-        if (auto binding_point = var->Declaration()->BindingPoint()) {
+        if (auto binding_point = global->Declaration()->BindingPoint()) {
-            ret.push_back({var, binding_point});
+            ret.push_back({global, binding_point});
         }
     }
     return ret;
@@ -89,10 +89,10 @@ std::vector<std::pair<const Variable*, const ast::BuiltinAttribute*>>
 Function::TransitivelyReferencedBuiltinVariables() const {
     std::vector<std::pair<const Variable*, const ast::BuiltinAttribute*>> ret;
 
-    for (auto* var : TransitivelyReferencedGlobals()) {
+    for (auto* global : TransitivelyReferencedGlobals()) {
-        for (auto* attr : var->Declaration()->attributes) {
+        for (auto* attr : global->Declaration()->attributes) {
             if (auto* builtin = attr->As<ast::BuiltinAttribute>()) {
-                ret.push_back({var, builtin});
+                ret.push_back({global, builtin});
                 break;
             }
         }
@@ -119,11 +119,11 @@ Function::VariableBindings Function::TransitivelyReferencedMultisampledTextureVa
 Function::VariableBindings Function::TransitivelyReferencedVariablesOfType(
     const tint::TypeInfo* type) const {
     VariableBindings ret;
-    for (auto* var : TransitivelyReferencedGlobals()) {
+    for (auto* global : TransitivelyReferencedGlobals()) {
-        auto* unwrapped_type = var->Type()->UnwrapRef();
+        auto* unwrapped_type = global->Type()->UnwrapRef();
         if (unwrapped_type->TypeInfo().Is(type)) {
-            if (auto binding_point = var->Declaration()->BindingPoint()) {
+            if (auto binding_point = global->Declaration()->BindingPoint()) {
-                ret.push_back({var, binding_point});
+                ret.push_back({global, binding_point});
             }
         }
     }
@@ -143,15 +143,15 @@ Function::VariableBindings Function::TransitivelyReferencedSamplerVariablesImpl(
     ast::SamplerKind kind) const {
     VariableBindings ret;
 
-    for (auto* var : TransitivelyReferencedGlobals()) {
+    for (auto* global : TransitivelyReferencedGlobals()) {
-        auto* unwrapped_type = var->Type()->UnwrapRef();
+        auto* unwrapped_type = global->Type()->UnwrapRef();
         auto* sampler = unwrapped_type->As<sem::Sampler>();
         if (sampler == nullptr || sampler->kind() != kind) {
             continue;
         }
 
-        if (auto binding_point = var->Declaration()->BindingPoint()) {
+        if (auto binding_point = global->Declaration()->BindingPoint()) {
-            ret.push_back({var, binding_point});
+            ret.push_back({global, binding_point});
         }
     }
     return ret;
@@ -161,8 +161,8 @@ Function::VariableBindings Function::TransitivelyReferencedSampledTextureVariabl
     bool multisampled) const {
     VariableBindings ret;
 
-    for (auto* var : TransitivelyReferencedGlobals()) {
+    for (auto* global : TransitivelyReferencedGlobals()) {
-        auto* unwrapped_type = var->Type()->UnwrapRef();
+        auto* unwrapped_type = global->Type()->UnwrapRef();
         auto* texture = unwrapped_type->As<sem::Texture>();
         if (texture == nullptr) {
             continue;
@@ -175,8 +175,8 @@ Function::VariableBindings Function::TransitivelyReferencedSampledTextureVariabl
             continue;
         }
 
-        if (auto binding_point = var->Declaration()->BindingPoint()) {
+        if (auto binding_point = global->Declaration()->BindingPoint()) {
-            ret.push_back({var, binding_point});
+            ret.push_back({global, binding_point});
         }
     }
 

src/tint/sem/type_mappings.h

@@ -27,6 +27,7 @@ class Function;
 class IfStatement;
 class MemberAccessorExpression;
 class Node;
+class Override;
 class Statement;
 class Struct;
 class StructMember;
@@ -45,6 +46,7 @@ class Function;
 class IfStatement;
 class MemberAccessorExpression;
 class Node;
+class GlobalVariable;
 class Statement;
 class Struct;
 class StructMember;
@@ -69,6 +71,7 @@ struct TypeMappings {
     IfStatement* operator()(ast::IfStatement*);
     MemberAccessorExpression* operator()(ast::MemberAccessorExpression*);
     Node* operator()(ast::Node*);
+    GlobalVariable* operator()(ast::Override*);
     Statement* operator()(ast::Statement*);
     Struct* operator()(ast::Struct*);
     StructMember* operator()(ast::StructMember*);

src/tint/sem/variable.cc

@@ -62,7 +62,7 @@ GlobalVariable::GlobalVariable(const ast::Variable* declaration,
 
 GlobalVariable::~GlobalVariable() = default;
 
-Parameter::Parameter(const ast::Variable* declaration,
+Parameter::Parameter(const ast::Parameter* declaration,
                      uint32_t index,
                      const sem::Type* type,
                      ast::StorageClass storage_class,

src/tint/sem/variable.h

@@ -154,24 +154,14 @@ class GlobalVariable final : public Castable<GlobalVariable, Variable> {
     sem::BindingPoint BindingPoint() const { return binding_point_; }
 
     /// @param id the constant identifier to assign to this variable
-    void SetConstantId(uint16_t id) {
+    void SetConstantId(uint16_t id) { constant_id_ = id; }
-        constant_id_ = id;
-        is_overridable_ = true;
-    }
 
     /// @returns the pipeline constant ID associated with the variable
     uint16_t ConstantId() const { return constant_id_; }
 
-    /// @param is_overridable true if this is a pipeline overridable constant
-    void SetIsOverridable(bool is_overridable = true) { is_overridable_ = is_overridable; }
-
-    /// @returns true if this is pipeline overridable constant
-    bool IsOverridable() const { return is_overridable_; }
-
   private:
     const sem::BindingPoint binding_point_;
 
-    bool is_overridable_ = false;
     uint16_t constant_id_ = 0;
 };
 
@@ -185,7 +175,7 @@ class Parameter final : public Castable<Parameter, Variable> {
     /// @param storage_class the variable storage class
     /// @param access the variable access control type
     /// @param usage the semantic usage for the parameter
-    Parameter(const ast::Variable* declaration,
+    Parameter(const ast::Parameter* declaration,
               uint32_t index,
               const sem::Type* type,
               ast::StorageClass storage_class,

src/tint/transform/add_spirv_block_attribute.cc

@@ -54,8 +54,8 @@ void AddSpirvBlockAttribute::Run(CloneContext& ctx, const DataMap&, DataMap&) co
     // contains it in the destination program.
     std::unordered_map<const sem::Type*, const ast::Struct*> wrapper_structs;
 
-    // Process global variables that are buffers.
+    // Process global 'var' declarations that are buffers.
-    for (auto* var : ctx.src->AST().GlobalVariables()) {
+    for (auto* var : ctx.src->AST().Globals<ast::Var>()) {
         auto* sem_var = sem.Get<sem::GlobalVariable>(var);
         if (var->declared_storage_class != ast::StorageClass::kStorage &&
             var->declared_storage_class != ast::StorageClass::kUniform) {

src/tint/transform/binding_remapper.cc

@@ -67,8 +67,8 @@ void BindingRemapper::Run(CloneContext& ctx, const DataMap& inputs, DataMap&) co
             }
             auto* func = ctx.src->Sem().Get(func_ast);
             std::unordered_map<sem::BindingPoint, int> binding_point_counts;
-            for (auto* var : func->TransitivelyReferencedGlobals()) {
+            for (auto* global : func->TransitivelyReferencedGlobals()) {
-                if (auto binding_point = var->Declaration()->BindingPoint()) {
+                if (auto binding_point = global->Declaration()->BindingPoint()) {
                     BindingPoint from{binding_point.group->value, binding_point.binding->value};
                     auto bp_it = remappings->binding_points.find(from);
                     if (bp_it != remappings->binding_points.end()) {
@@ -88,7 +88,7 @@ void BindingRemapper::Run(CloneContext& ctx, const DataMap& inputs, DataMap&) co
         }
     }
 
-    for (auto* var : ctx.src->AST().GlobalVariables()) {
+    for (auto* var : ctx.src->AST().Globals<ast::Var>()) {
         if (auto binding_point = var->BindingPoint()) {
             // The original binding point
             BindingPoint from{binding_point.group->value, binding_point.binding->value};
@@ -130,10 +130,10 @@ void BindingRemapper::Run(CloneContext& ctx, const DataMap& inputs, DataMap&) co
                 }
                 auto* ty = sem->Type()->UnwrapRef();
                 const ast::Type* inner_ty = CreateASTTypeFor(ctx, ty);
-                auto* new_var = ctx.dst->create<ast::Variable>(
+                auto* new_var =
-                    ctx.Clone(var->source), ctx.Clone(var->symbol), var->declared_storage_class, ac,
+                    ctx.dst->Var(ctx.Clone(var->source), ctx.Clone(var->symbol), inner_ty,
-                    inner_ty, false, false, ctx.Clone(var->constructor),
+                                 var->declared_storage_class, ac, ctx.Clone(var->constructor),
-                    ctx.Clone(var->attributes));
+                                 ctx.Clone(var->attributes));
                 ctx.Replace(var, new_var);
             }
 

src/tint/transform/combine_samplers.cc

@@ -147,16 +147,16 @@ struct CombineSamplers::State {
 
         // Remove all texture and sampler global variables. These will be replaced
         // by combined samplers.
-        for (auto* var : ctx.src->AST().GlobalVariables()) {
+        for (auto* global : ctx.src->AST().GlobalVariables()) {
-            auto* type = sem.Get(var->type);
+            auto* type = sem.Get(global->type);
-            if (type && type->IsAnyOf<sem::Texture, sem::Sampler>() &&
+            if (tint::IsAnyOf<sem::Texture, sem::Sampler>(type) &&
                 !type->Is<sem::StorageTexture>()) {
-                ctx.Remove(ctx.src->AST().GlobalDeclarations(), var);
+                ctx.Remove(ctx.src->AST().GlobalDeclarations(), global);
-            } else if (auto binding_point = var->BindingPoint()) {
+            } else if (auto binding_point = global->BindingPoint()) {
                 if (binding_point.group->value == 0 && binding_point.binding->value == 0) {
                     auto* attribute =
                         ctx.dst->Disable(ast::DisabledValidation::kBindingPointCollision);
-                    ctx.InsertFront(var->attributes, attribute);
+                    ctx.InsertFront(global->attributes, attribute);
                 }
             }
         }
@@ -188,9 +188,8 @@ struct CombineSamplers::State {
                     } else {
                         // Either texture or sampler (or both) is a function parameter;
                         // add a new function parameter to represent the combined sampler.
-                        const ast::Type* type = CreateCombinedASTTypeFor(texture_var, sampler_var);
+                        auto* type = CreateCombinedASTTypeFor(texture_var, sampler_var);
-                        const ast::Variable* var =
+                        auto* var = ctx.dst->Param(ctx.dst->Symbols().New(name), type);
-                            ctx.dst->Param(ctx.dst->Symbols().New(name), type);
                         params.push_back(var);
                         function_combined_texture_samplers_[func][pair] = var;
                     }

src/tint/transform/fold_trivial_single_use_lets.cc

@@ -31,11 +31,11 @@ const ast::VariableDeclStatement* AsTrivialLetDecl(const ast::Statement* stmt) {
     if (!var_decl) {
         return nullptr;
     }
-    auto* var = var_decl->variable;
+    auto* let = var_decl->variable->As<ast::Let>();
-    if (!var->is_const) {
+    if (!let) {
         return nullptr;
     }
-    auto* ctor = var->constructor;
+    auto* ctor = let->constructor;
     if (!IsAnyOf<ast::IdentifierExpression, ast::LiteralExpression>(ctor)) {
         return nullptr;
     }

src/tint/transform/module_scope_var_to_entry_point_param.cc

@@ -155,9 +155,13 @@ struct ModuleScopeVarToEntryPointParam::State {
                 return workgroup_parameter_symbol;
             };
 
-            for (auto* var : func_sem->TransitivelyReferencedGlobals()) {
+            for (auto* global : func_sem->TransitivelyReferencedGlobals()) {
-                auto sc = var->StorageClass();
+                auto* var = global->Declaration()->As<ast::Var>();
-                auto* ty = var->Type()->UnwrapRef();
+                if (!var) {
+                    continue;
+                }
+                auto sc = global->StorageClass();
+                auto* ty = global->Type()->UnwrapRef();
                 if (sc == ast::StorageClass::kNone) {
                     continue;
                 }
@@ -182,12 +186,12 @@ struct ModuleScopeVarToEntryPointParam::State {
                 bool is_wrapped = false;
 
                 if (is_entry_point) {
-                    if (var->Type()->UnwrapRef()->is_handle()) {
+                    if (global->Type()->UnwrapRef()->is_handle()) {
                         // For a texture or sampler variable, redeclare it as an entry point
                         // parameter. Disable entry point parameter validation.
                         auto* disable_validation =
                             ctx.dst->Disable(ast::DisabledValidation::kEntryPointParameter);
-                        auto attrs = ctx.Clone(var->Declaration()->attributes);
+                        auto attrs = ctx.Clone(var->attributes);
                         attrs.push_back(disable_validation);
                         auto* param = ctx.dst->Param(new_var_symbol, store_type(), attrs);
                         ctx.InsertFront(func_ast->params, param);
@@ -195,7 +199,7 @@ struct ModuleScopeVarToEntryPointParam::State {
                                sc == ast::StorageClass::kUniform) {
                         // Variables into the Storage and Uniform storage classes are
                         // redeclared as entry point parameters with a pointer type.
-                        auto attributes = ctx.Clone(var->Declaration()->attributes);
+                        auto attributes = ctx.Clone(var->attributes);
                         attributes.push_back(
                             ctx.dst->Disable(ast::DisabledValidation::kEntryPointParameter));
                         attributes.push_back(
@@ -214,22 +218,22 @@ struct ModuleScopeVarToEntryPointParam::State {
                             is_wrapped = true;
                         }
 
-                        param_type = ctx.dst->ty.pointer(param_type, sc,
+                        param_type = ctx.dst->ty.pointer(param_type, sc, var->declared_access);
-                                                         var->Declaration()->declared_access);
                         auto* param = ctx.dst->Param(new_var_symbol, param_type, attributes);
                         ctx.InsertFront(func_ast->params, param);
                         is_pointer = true;
-                    } else if (sc == ast::StorageClass::kWorkgroup && ContainsMatrix(var->Type())) {
+                    } else if (sc == ast::StorageClass::kWorkgroup &&
+                               ContainsMatrix(global->Type())) {
                         // Due to a bug in the MSL compiler, we use a threadgroup memory
                         // argument for any workgroup allocation that contains a matrix.
                         // See crbug.com/tint/938.
                         // TODO(jrprice): Do this for all other workgroup variables too.
 
                         // Create a member in the workgroup parameter struct.
-                        auto member = ctx.Clone(var->Declaration()->symbol);
+                        auto member = ctx.Clone(var->symbol);
                         workgroup_parameter_members.push_back(
                             ctx.dst->Member(member, store_type()));
-                        CloneStructTypes(var->Type()->UnwrapRef());
+                        CloneStructTypes(global->Type()->UnwrapRef());
 
                         // Create a function-scope variable that is a pointer to the member.
                         auto* member_ptr = ctx.dst->AddressOf(
@@ -246,7 +250,7 @@ struct ModuleScopeVarToEntryPointParam::State {
                         // this variable.
                         auto* disable_validation =
                             ctx.dst->Disable(ast::DisabledValidation::kIgnoreStorageClass);
-                        auto* constructor = ctx.Clone(var->Declaration()->constructor);
+                        auto* constructor = ctx.Clone(var->constructor);
                         auto* local_var =
                             ctx.dst->Var(new_var_symbol, store_type(), sc, constructor,
                                          ast::AttributeList{disable_validation});
@@ -257,9 +261,8 @@ struct ModuleScopeVarToEntryPointParam::State {
                     // Use a pointer for non-handle types.
                     auto* param_type = store_type();
                     ast::AttributeList attributes;
-                    if (!var->Type()->UnwrapRef()->is_handle()) {
+                    if (!global->Type()->UnwrapRef()->is_handle()) {
-                        param_type = ctx.dst->ty.pointer(param_type, sc,
+                        param_type = ctx.dst->ty.pointer(param_type, sc, var->declared_access);
-                                                         var->Declaration()->declared_access);
                         is_pointer = true;
 
                         // Disable validation of the parameter's storage class and of
@@ -275,7 +278,7 @@ struct ModuleScopeVarToEntryPointParam::State {
 
                 // Replace all uses of the module-scope variable.
                 // For non-entry points, dereference non-handle pointer parameters.
-                for (auto* user : var->Users()) {
+                for (auto* user : global->Users()) {
                     if (user->Stmt()->Function()->Declaration() == func_ast) {
                         const ast::Expression* expr = ctx.dst->Expr(new_var_symbol);
                         if (is_pointer) {
@@ -298,7 +301,7 @@ struct ModuleScopeVarToEntryPointParam::State {
                     }
                 }
 
-                var_to_newvar[var] = {new_var_symbol, is_pointer, is_wrapped};
+                var_to_newvar[global] = {new_var_symbol, is_pointer, is_wrapped};
             }
 
             if (!workgroup_parameter_members.empty()) {

src/tint/transform/multiplanar_external_texture.cc

@@ -86,8 +86,8 @@ struct MultiplanarExternalTexture::State {
         // binding and create two additional bindings (one texture_2d<f32> to
         // represent the secondary plane and one uniform buffer for the
         // ExternalTextureParams struct).
-        for (auto* var : ctx.src->AST().GlobalVariables()) {
+        for (auto* global : ctx.src->AST().GlobalVariables()) {
-            auto* sem_var = sem.Get(var);
+            auto* sem_var = sem.Get(global);
             if (!sem_var->Type()->UnwrapRef()->Is<sem::ExternalTexture>()) {
                 continue;
             }
@@ -95,7 +95,7 @@ struct MultiplanarExternalTexture::State {
             // If the attributes are empty, then this must be a texture_external
             // passed as a function parameter. These variables are transformed
             // elsewhere.
-            if (var->attributes.empty()) {
+            if (global->attributes.empty()) {
                 continue;
             }
 
@@ -109,8 +109,8 @@ struct MultiplanarExternalTexture::State {
             // provided to this transform. We fetch the new binding points by
             // providing the original texture_external binding points into the
             // passed map.
-            BindingPoint bp = {var->BindingPoint().group->value,
+            BindingPoint bp = {global->BindingPoint().group->value,
-                               var->BindingPoint().binding->value};
+                               global->BindingPoint().binding->value};
 
             BindingsMap::const_iterator it = new_binding_points->bindings_map.find(bp);
             if (it == new_binding_points->bindings_map.end()) {
@@ -129,7 +129,7 @@ struct MultiplanarExternalTexture::State {
             // corresponds with the new destination bindings.
             // NewBindingSymbols new_binding_syms;
             auto& syms = new_binding_symbols[sem_var];
-            syms.plane_0 = ctx.Clone(var->symbol);
+            syms.plane_0 = ctx.Clone(global->symbol);
             syms.plane_1 = b.Symbols().New("ext_tex_plane_1");
             b.Global(syms.plane_1, b.ty.sampled_texture(ast::TextureDimension::k2d, b.ty.f32()),
                      b.GroupAndBinding(bps.plane_1.group, bps.plane_1.binding));
@@ -140,13 +140,13 @@ struct MultiplanarExternalTexture::State {
 
             // Replace the original texture_external binding with a texture_2d<f32>
             // binding.
-            ast::AttributeList cloned_attributes = ctx.Clone(var->attributes);
+            ast::AttributeList cloned_attributes = ctx.Clone(global->attributes);
-            const ast::Expression* cloned_constructor = ctx.Clone(var->constructor);
+            const ast::Expression* cloned_constructor = ctx.Clone(global->constructor);
 
             auto* replacement =
                 b.Var(syms.plane_0, b.ty.sampled_texture(ast::TextureDimension::k2d, b.ty.f32()),
                       cloned_constructor, cloned_attributes);
-            ctx.Replace(var, replacement);
+            ctx.Replace(global, replacement);
         }
 
         // We must update all the texture_external parameters for user declared

src/tint/transform/num_workgroups_from_uniform.cc

@@ -133,8 +133,8 @@ void NumWorkgroupsFromUniform::Run(CloneContext& ctx, const DataMap& inputs, Dat
                 // plus 1, or group 0 if no resource bound.
                 group = 0;
 
-                for (auto* var : ctx.src->AST().GlobalVariables()) {
+                for (auto* global : ctx.src->AST().GlobalVariables()) {
-                    if (auto binding_point = var->BindingPoint()) {
+                    if (auto binding_point = global->BindingPoint()) {
                         if (binding_point.group->value >= group) {
                             group = binding_point.group->value + 1;
                         }

src/tint/transform/simplify_pointers.cc

@@ -109,8 +109,8 @@ struct SimplifyPointers::State {
             }
             if (auto* user = ctx.src->Sem().Get<sem::VariableUser>(op.expr)) {
                 auto* var = user->Variable();
-                if (var->Is<sem::LocalVariable>() &&  //
+                if (var->Is<sem::LocalVariable>() &&       //
-                    var->Declaration()->is_const &&   //
+                    var->Declaration()->Is<ast::Let>() &&  //
                     var->Type()->Is<sem::Pointer>()) {
                     op.expr = var->Declaration()->constructor;
                     continue;
@@ -161,7 +161,7 @@ struct SimplifyPointers::State {
         // permitted.
         for (auto* node : ctx.src->ASTNodes().Objects()) {
             if (auto* let = node->As<ast::VariableDeclStatement>()) {
-                if (!let->variable->is_const) {
+                if (!let->variable->Is<ast::Let>()) {
                     continue;  // Not a `let` declaration. Ignore.
                 }
 

src/tint/transform/single_entry_point.cc

@@ -64,38 +64,43 @@ void SingleEntryPoint::Run(CloneContext& ctx, const DataMap& inputs, DataMap&) c
         referenced_vars.emplace(var->Declaration());
     }
 
-    // Clone any module-scope variables, types, and functions that are statically
+    // Clone any module-scope variables, types, and functions that are statically referenced by the
-    // referenced by the target entry point.
+    // target entry point.
     for (auto* decl : ctx.src->AST().GlobalDeclarations()) {
-        if (auto* ty = decl->As<ast::TypeDecl>()) {
+        Switch(
-            // TODO(jrprice): Strip unused types.
+            decl,  //
-            ctx.dst->AST().AddTypeDecl(ctx.Clone(ty));
+            [&](const ast::TypeDecl* ty) {
-        } else if (auto* var = decl->As<ast::Variable>()) {
+                // TODO(jrprice): Strip unused types.
-            if (referenced_vars.count(var)) {
+                ctx.dst->AST().AddTypeDecl(ctx.Clone(ty));
-                if (var->is_overridable) {
+            },
-                    // It is an overridable constant
+            [&](const ast::Override* override) {
-                    if (!ast::HasAttribute<ast::IdAttribute>(var->attributes)) {
+                if (referenced_vars.count(override)) {
+                    if (!ast::HasAttribute<ast::IdAttribute>(override->attributes)) {
                         // If the constant doesn't already have an @id() attribute, add one
                         // so that its allocated ID so that it won't be affected by other
                         // stripped away constants
-                        auto* global = sem.Get(var)->As<sem::GlobalVariable>();
+                        auto* global = sem.Get(override);
                         const auto* id = ctx.dst->Id(global->ConstantId());
-                        ctx.InsertFront(var->attributes, id);
+                        ctx.InsertFront(override->attributes, id);
                     }
+                    ctx.dst->AST().AddGlobalVariable(ctx.Clone(override));
                 }
-                ctx.dst->AST().AddGlobalVariable(ctx.Clone(var));
+            },
-            }
+            [&](const ast::Variable* v) {  // var, let
-        } else if (auto* func = decl->As<ast::Function>()) {
+                if (referenced_vars.count(v)) {
-            if (sem.Get(func)->HasAncestorEntryPoint(entry_point->symbol)) {
+                    ctx.dst->AST().AddGlobalVariable(ctx.Clone(v));
-                ctx.dst->AST().AddFunction(ctx.Clone(func));
+                }
-            }
+            },
-        } else if (auto* ext = decl->As<ast::Enable>()) {
+            [&](const ast::Function* func) {
-            ctx.dst->AST().AddEnable(ctx.Clone(ext));
+                if (sem.Get(func)->HasAncestorEntryPoint(entry_point->symbol)) {
-        } else {
+                    ctx.dst->AST().AddFunction(ctx.Clone(func));
-            TINT_UNREACHABLE(Transform, ctx.dst->Diagnostics())
+                }
-                << "unhandled global declaration: " << decl->TypeInfo().name;
+            },
-            return;
+            [&](const ast::Enable* ext) { ctx.dst->AST().AddEnable(ctx.Clone(ext)); },
-        }
+            [&](Default) {
+                TINT_UNREACHABLE(Transform, ctx.dst->Diagnostics())
+                    << "unhandled global declaration: " << decl->TypeInfo().name;
+            });
     }
 
     // Clone the entry point.

src/tint/transform/unshadow.cc

@@ -44,28 +44,42 @@ struct Unshadow::State {
         // Maps a variable to its new name.
         std::unordered_map<const sem::Variable*, Symbol> renamed_to;
 
-        auto rename = [&](const sem::Variable* var) -> const ast::Variable* {
+        auto rename = [&](const sem::Variable* v) -> const ast::Variable* {
-            auto* decl = var->Declaration();
+            auto* decl = v->Declaration();
             auto name = ctx.src->Symbols().NameFor(decl->symbol);
             auto symbol = ctx.dst->Symbols().New(name);
-            renamed_to.emplace(var, symbol);
+            renamed_to.emplace(v, symbol);
 
             auto source = ctx.Clone(decl->source);
             auto* type = ctx.Clone(decl->type);
             auto* constructor = ctx.Clone(decl->constructor);
             auto attributes = ctx.Clone(decl->attributes);
-            return ctx.dst->create<ast::Variable>(source, symbol, decl->declared_storage_class,
+            return Switch(
-                                                  decl->declared_access, type, decl->is_const,
+                decl,  //
-                                                  decl->is_overridable, constructor, attributes);
+                [&](const ast::Var* var) {
+                    return ctx.dst->Var(source, symbol, type, var->declared_storage_class,
+                                        var->declared_access, constructor, attributes);
+                },
+                [&](const ast::Let*) {
+                    return ctx.dst->Let(source, symbol, type, constructor, attributes);
+                },
+                [&](const ast::Parameter*) {
+                    return ctx.dst->Param(source, symbol, type, attributes);
+                },
+                [&](Default) {
+                    TINT_ICE(Transform, ctx.dst->Diagnostics())
+                        << "unexpected variable type: " << decl->TypeInfo().name;
+                    return nullptr;
+                });
         };
 
-        ctx.ReplaceAll([&](const ast::Variable* var) -> const ast::Variable* {
+        ctx.ReplaceAll([&](const ast::Variable* v) -> const ast::Variable* {
-            if (auto* local = sem.Get<sem::LocalVariable>(var)) {
+            if (auto* local = sem.Get<sem::LocalVariable>(v)) {
                 if (local->Shadows()) {
                     return rename(local);
                 }
             }
-            if (auto* param = sem.Get<sem::Parameter>(var)) {
+            if (auto* param = sem.Get<sem::Parameter>(v)) {
                 if (param->Shadows()) {
                     return rename(param);
                 }

src/tint/transform/utils/hoist_to_decl_before.cc

@@ -189,18 +189,18 @@ class HoistToDeclBefore::State {
     /// before `before_expr`.
     /// @param before_expr expression to insert `expr` before
     /// @param expr expression to hoist
-    /// @param as_const hoist to `let` if true, otherwise to `var`
+    /// @param as_let hoist to `let` if true, otherwise to `var`
     /// @param decl_name optional name to use for the variable/constant name
     /// @return true on success
     bool Add(const sem::Expression* before_expr,
              const ast::Expression* expr,
-             bool as_const,
+             bool as_let,
              const char* decl_name) {
         auto name = b.Symbols().New(decl_name);
 
         // Construct the let/var that holds the hoisted expr
-        auto* v = as_const ? b.Let(name, nullptr, ctx.Clone(expr))
+        auto* v = as_let ? static_cast<const ast::Variable*>(b.Let(name, nullptr, ctx.Clone(expr)))
-                           : b.Var(name, nullptr, ctx.Clone(expr));
+                         : static_cast<const ast::Variable*>(b.Var(name, nullptr, ctx.Clone(expr)));
         auto* decl = b.Decl(v);
 
         if (!InsertBefore(before_expr->Stmt(), decl)) {
@@ -330,9 +330,9 @@ HoistToDeclBefore::~HoistToDeclBefore() {}
 
 bool HoistToDeclBefore::Add(const sem::Expression* before_expr,
                             const ast::Expression* expr,
-                            bool as_const,
+                            bool as_let,
                             const char* decl_name) {
-    return state_->Add(before_expr, expr, as_const, decl_name);
+    return state_->Add(before_expr, expr, as_let, decl_name);
 }
 
 bool HoistToDeclBefore::InsertBefore(const sem::Statement* before_stmt,

src/tint/transform/vertex_pulling.cc

@@ -695,7 +695,7 @@ struct State {
     /// vertex_index and instance_index builtins if present.
     /// @param func the entry point function
     /// @param param the parameter to process
-    void ProcessNonStructParameter(const ast::Function* func, const ast::Variable* param) {
+    void ProcessNonStructParameter(const ast::Function* func, const ast::Parameter* param) {
         if (auto* location = ast::GetAttribute<ast::LocationAttribute>(param->attributes)) {
             // Create a function-scope variable to replace the parameter.
             auto func_var_sym = ctx.Clone(param->symbol);
@@ -733,7 +733,7 @@ struct State {
     /// @param param the parameter to process
     /// @param struct_ty the structure type
     void ProcessStructParameter(const ast::Function* func,
-                                const ast::Variable* param,
+                                const ast::Parameter* param,
                                 const ast::Struct* struct_ty) {
         auto param_sym = ctx.Clone(param->symbol);
 

src/tint/transform/zero_init_workgroup_memory.cc

@@ -416,8 +416,8 @@ ZeroInitWorkgroupMemory::ZeroInitWorkgroupMemory() = default;
 ZeroInitWorkgroupMemory::~ZeroInitWorkgroupMemory() = default;
 
 bool ZeroInitWorkgroupMemory::ShouldRun(const Program* program, const DataMap&) const {
-    for (auto* decl : program->AST().GlobalDeclarations()) {
+    for (auto* global : program->AST().GlobalVariables()) {
-        if (auto* var = decl->As<ast::Variable>()) {
+        if (auto* var = global->As<ast::Var>()) {
             if (var->declared_storage_class == ast::StorageClass::kWorkgroup) {
                 return true;
             }

src/tint/writer/glsl/generator_impl.cc

@@ -1904,42 +1904,47 @@ bool GeneratorImpl::EmitFunction(const ast::Function* func) {
 }
 
 bool GeneratorImpl::EmitGlobalVariable(const ast::Variable* global) {
-    if (global->is_const) {
+    return Switch(
-        return EmitProgramConstVariable(global);
+        global,  //
-    }
+        [&](const ast::Var* var) {
-
+            auto* sem = builder_.Sem().Get(global);
-    auto* sem = builder_.Sem().Get(global);
+            switch (sem->StorageClass()) {
-    switch (sem->StorageClass()) {
+                case ast::StorageClass::kUniform:
-        case ast::StorageClass::kUniform:
+                    return EmitUniformVariable(var, sem);
-            return EmitUniformVariable(sem);
+                case ast::StorageClass::kStorage:
-        case ast::StorageClass::kStorage:
+                    return EmitStorageVariable(var, sem);
-            return EmitStorageVariable(sem);
+                case ast::StorageClass::kHandle:
-        case ast::StorageClass::kHandle:
+                    return EmitHandleVariable(var, sem);
-            return EmitHandleVariable(sem);
+                case ast::StorageClass::kPrivate:
-        case ast::StorageClass::kPrivate:
+                    return EmitPrivateVariable(sem);
-            return EmitPrivateVariable(sem);
+                case ast::StorageClass::kWorkgroup:
-        case ast::StorageClass::kWorkgroup:
+                    return EmitWorkgroupVariable(sem);
-            return EmitWorkgroupVariable(sem);
+                case ast::StorageClass::kInput:
-        case ast::StorageClass::kInput:
+                case ast::StorageClass::kOutput:
-        case ast::StorageClass::kOutput:
+                    return EmitIOVariable(sem);
-            return EmitIOVariable(sem);
+                default:
-        default:
+                    TINT_ICE(Writer, diagnostics_)
-            break;
+                        << "unhandled storage class " << sem->StorageClass();
-    }
+                    return false;
-
+            }
-    TINT_ICE(Writer, diagnostics_) << "unhandled storage class " << sem->StorageClass();
+        },
-    return false;
+        [&](const ast::Let* let) { return EmitProgramConstVariable(let); },
+        [&](const ast::Override* override) { return EmitOverride(override); },
+        [&](Default) {
+            TINT_ICE(Writer, diagnostics_)
+                << "unhandled global variable type " << global->TypeInfo().name;
+            return false;
+        });
 }
 
-bool GeneratorImpl::EmitUniformVariable(const sem::Variable* var) {
+bool GeneratorImpl::EmitUniformVariable(const ast::Var* var, const sem::Variable* sem) {
-    auto* decl = var->Declaration();
+    auto* type = sem->Type()->UnwrapRef();
-    auto* type = var->Type()->UnwrapRef();
     auto* str = type->As<sem::Struct>();
     if (!str) {
         TINT_ICE(Writer, builder_.Diagnostics()) << "storage variable must be of struct type";
         return false;
     }
-    ast::VariableBindingPoint bp = decl->BindingPoint();
+    ast::VariableBindingPoint bp = var->BindingPoint();
     {
         auto out = line();
         out << "layout(binding = " << bp.binding->value;
@@ -1949,36 +1954,34 @@ bool GeneratorImpl::EmitUniformVariable(const sem::Variable* var) {
         out << ") uniform " << UniqueIdentifier(StructName(str)) << " {";
     }
     EmitStructMembers(current_buffer_, str, /* emit_offsets */ true);
-    auto name = builder_.Symbols().NameFor(decl->symbol);
+    auto name = builder_.Symbols().NameFor(var->symbol);
     line() << "} " << name << ";";
     line();
 
     return true;
 }
 
-bool GeneratorImpl::EmitStorageVariable(const sem::Variable* var) {
+bool GeneratorImpl::EmitStorageVariable(const ast::Var* var, const sem::Variable* sem) {
-    auto* decl = var->Declaration();
+    auto* type = sem->Type()->UnwrapRef();
-    auto* type = var->Type()->UnwrapRef();
     auto* str = type->As<sem::Struct>();
     if (!str) {
         TINT_ICE(Writer, builder_.Diagnostics()) << "storage variable must be of struct type";
         return false;
     }
-    ast::VariableBindingPoint bp = decl->BindingPoint();
+    ast::VariableBindingPoint bp = var->BindingPoint();
     line() << "layout(binding = " << bp.binding->value << ", std430) buffer "
            << UniqueIdentifier(StructName(str)) << " {";
     EmitStructMembers(current_buffer_, str, /* emit_offsets */ true);
-    auto name = builder_.Symbols().NameFor(decl->symbol);
+    auto name = builder_.Symbols().NameFor(var->symbol);
     line() << "} " << name << ";";
     return true;
 }
 
-bool GeneratorImpl::EmitHandleVariable(const sem::Variable* var) {
+bool GeneratorImpl::EmitHandleVariable(const ast::Var* var, const sem::Variable* sem) {
-    auto* decl = var->Declaration();
     auto out = line();
 
-    auto name = builder_.Symbols().NameFor(decl->symbol);
+    auto name = builder_.Symbols().NameFor(var->symbol);
-    auto* type = var->Type()->UnwrapRef();
+    auto* type = sem->Type()->UnwrapRef();
     if (type->Is<sem::Sampler>()) {
         // GLSL ignores Sampler variables.
         return true;
@@ -1986,7 +1989,7 @@ bool GeneratorImpl::EmitHandleVariable(const sem::Variable* var) {
     if (auto* storage = type->As<sem::StorageTexture>()) {
         out << "layout(" << convert_texel_format_to_glsl(storage->texel_format()) << ") ";
     }
-    if (!EmitTypeAndName(out, type, var->StorageClass(), var->Access(), name)) {
+    if (!EmitTypeAndName(out, type, sem->StorageClass(), sem->Access(), name)) {
         return false;
     }
 
@@ -2138,7 +2141,7 @@ bool GeneratorImpl::EmitEntryPointFunction(const ast::Function* func) {
 
             if (wgsize[i].overridable_const) {
                 auto* global = builder_.Sem().Get<sem::GlobalVariable>(wgsize[i].overridable_const);
-                if (!global->IsOverridable()) {
+                if (!global->Declaration()->Is<ast::Override>()) {
                     TINT_ICE(Writer, builder_.Diagnostics())
                         << "expected a pipeline-overridable constant";
                 }
@@ -2652,7 +2655,15 @@ bool GeneratorImpl::EmitStatement(const ast::Statement* stmt) {
         return EmitSwitch(s);
     }
     if (auto* v = stmt->As<ast::VariableDeclStatement>()) {
-        return EmitVariable(v->variable);
+        return Switch(
+            v->variable,  //
+            [&](const ast::Var* var) { return EmitVar(var); },
+            [&](const ast::Let* let) { return EmitLet(let); },
+            [&](Default) {  //
+                TINT_ICE(Writer, diagnostics_)
+                    << "unknown variable type: " << v->variable->TypeInfo().name;
+                return false;
+            });
     }
 
     diagnostics_.add_error(diag::System::Writer,
@@ -2934,18 +2945,11 @@ bool GeneratorImpl::EmitUnaryOp(std::ostream& out, const ast::UnaryOpExpression*
     return true;
 }
 
-bool GeneratorImpl::EmitVariable(const ast::Variable* var) {
+bool GeneratorImpl::EmitVar(const ast::Var* var) {
     auto* sem = builder_.Sem().Get(var);
     auto* type = sem->Type()->UnwrapRef();
 
-    // TODO(dsinclair): Handle variable attributes
-    if (!var->attributes.empty()) {
-        diagnostics_.add_error(diag::System::Writer, "Variable attributes are not handled yet");
-        return false;
-    }
-
     auto out = line();
-    // TODO(senorblanco): handle const
     if (!EmitTypeAndName(out, type, sem->StorageClass(), sem->Access(),
                          builder_.Symbols().NameFor(var->symbol))) {
         return false;
@@ -2967,58 +2971,74 @@ bool GeneratorImpl::EmitVariable(const ast::Variable* var) {
     return true;
 }
 
-bool GeneratorImpl::EmitProgramConstVariable(const ast::Variable* var) {
+bool GeneratorImpl::EmitLet(const ast::Let* let) {
-    for (auto* d : var->attributes) {
+    auto* sem = builder_.Sem().Get(let);
-        if (!d->Is<ast::IdAttribute>()) {
+    auto* type = sem->Type()->UnwrapRef();
-            diagnostics_.add_error(diag::System::Writer, "Decorated const values not valid");
+
-            return false;
+    auto out = line();
-        }
+    // TODO(senorblanco): handle const
-    }
+    if (!EmitTypeAndName(out, type, ast::StorageClass::kNone, ast::Access::kUndefined,
-    if (!var->is_const) {
+                         builder_.Symbols().NameFor(let->symbol))) {
-        diagnostics_.add_error(diag::System::Writer, "Expected a const value");
         return false;
     }
 
+    out << " = ";
+
+    if (!EmitExpression(out, let->constructor)) {
+        return false;
+    }
+
+    out << ";";
+
+    return true;
+}
+
+bool GeneratorImpl::EmitProgramConstVariable(const ast::Variable* var) {
     auto* sem = builder_.Sem().Get(var);
     auto* type = sem->Type();
 
+    auto out = line();
+    out << "const ";
+    if (!EmitTypeAndName(out, type, ast::StorageClass::kNone, ast::Access::kUndefined,
+                         builder_.Symbols().NameFor(var->symbol))) {
+        return false;
+    }
+    out << " = ";
+    if (!EmitExpression(out, var->constructor)) {
+        return false;
+    }
+    out << ";";
+
+    return true;
+}
+
+bool GeneratorImpl::EmitOverride(const ast::Override* override) {
+    auto* sem = builder_.Sem().Get(override);
+    auto* type = sem->Type();
+
     auto* global = sem->As<sem::GlobalVariable>();
-    if (global && global->IsOverridable()) {
+    auto const_id = global->ConstantId();
-        auto const_id = global->ConstantId();
 
-        line() << "#ifndef " << kSpecConstantPrefix << const_id;
+    line() << "#ifndef " << kSpecConstantPrefix << const_id;
 
-        if (var->constructor != nullptr) {
+    if (override->constructor != nullptr) {
-            auto out = line();
+        auto out = line();
-            out << "#define " << kSpecConstantPrefix << const_id << " ";
+        out << "#define " << kSpecConstantPrefix << const_id << " ";
-            if (!EmitExpression(out, var->constructor)) {
+        if (!EmitExpression(out, override->constructor)) {
-                return false;
+            return false;
-            }
-        } else {
-            line() << "#error spec constant required for constant id " << const_id;
-        }
-        line() << "#endif";
-        {
-            auto out = line();
-            out << "const ";
-            if (!EmitTypeAndName(out, type, sem->StorageClass(), sem->Access(),
-                                 builder_.Symbols().NameFor(var->symbol))) {
-                return false;
-            }
-            out << " = " << kSpecConstantPrefix << const_id << ";";
         }
     } else {
+        line() << "#error spec constant required for constant id " << const_id;
+    }
+    line() << "#endif";
+    {
         auto out = line();
         out << "const ";
-        if (!EmitTypeAndName(out, type, sem->StorageClass(), sem->Access(),
+        if (!EmitTypeAndName(out, type, ast::StorageClass::kNone, ast::Access::kUndefined,
-                             builder_.Symbols().NameFor(var->symbol))) {
+                             builder_.Symbols().NameFor(override->symbol))) {
             return false;
         }
-        out << " = ";
+        out << " = " << kSpecConstantPrefix << const_id << ";";
-        if (!EmitExpression(out, var->constructor)) {
-            return false;
-        }
-        out << ";";
     }
 
     return true;

src/tint/writer/glsl/generator_impl.h

@@ -293,19 +293,22 @@ class GeneratorImpl : public TextGenerator {
     bool EmitGlobalVariable(const ast::Variable* global);
 
     /// Handles emitting a global variable with the uniform storage class
-    /// @param var the global variable
+    /// @param var the AST node for the 'var'
+    /// @param sem the semantic node for the 'var'
     /// @returns true on success
-    bool EmitUniformVariable(const sem::Variable* var);
+    bool EmitUniformVariable(const ast::Var* var, const sem::Variable* sem);
 
     /// Handles emitting a global variable with the storage storage class
-    /// @param var the global variable
+    /// @param var the AST node for the 'var'
+    /// @param sem the semantic node for the 'var'
     /// @returns true on success
-    bool EmitStorageVariable(const sem::Variable* var);
+    bool EmitStorageVariable(const ast::Var* var, const sem::Variable* sem);
 
     /// Handles emitting a global variable with the handle storage class
-    /// @param var the global variable
+    /// @param var the AST node for the 'var'
+    /// @param sem the semantic node for the 'var'
     /// @returns true on success
-    bool EmitHandleVariable(const sem::Variable* var);
+    bool EmitHandleVariable(const ast::Var* var, const sem::Variable* sem);
 
     /// Handles emitting a global variable with the private storage class
     /// @param var the global variable
@@ -437,14 +440,22 @@ class GeneratorImpl : public TextGenerator {
     /// @param type the type to emit the value for
     /// @returns true if the zero value was successfully emitted.
     bool EmitZeroValue(std::ostream& out, const sem::Type* type);
-    /// Handles generating a variable
+    /// Handles generating a 'var' declaration
     /// @param var the variable to generate
     /// @returns true if the variable was emitted
-    bool EmitVariable(const ast::Variable* var);
+    bool EmitVar(const ast::Var* var);
-    /// Handles generating a program scope constant variable
+    /// Handles generating a function-scope 'let' declaration
-    /// @param var the variable to emit
+    /// @param let the variable to generate
     /// @returns true if the variable was emitted
-    bool EmitProgramConstVariable(const ast::Variable* var);
+    bool EmitLet(const ast::Let* let);
+    /// Handles generating a module-scope 'let' declaration
+    /// @param let the 'let' to emit
+    /// @returns true if the variable was emitted
+    bool EmitProgramConstVariable(const ast::Variable* let);
+    /// Handles generating a module-scope 'override' declaration
+    /// @param override the 'override' to emit
+    /// @returns true if the variable was emitted
+    bool EmitOverride(const ast::Override* override);
     /// Handles generating a builtin method name
     /// @param builtin the semantic info for the builtin
     /// @returns the name or "" if not valid

src/tint/writer/glsl/generator_impl_module_constant_test.cc

@@ -40,7 +40,7 @@ TEST_F(GlslGeneratorImplTest_ModuleConstant, Emit_SpecConstant) {
 
     GeneratorImpl& gen = Build();
 
-    ASSERT_TRUE(gen.EmitProgramConstVariable(var)) << gen.error();
+    ASSERT_TRUE(gen.EmitOverride(var)) << gen.error();
     EXPECT_EQ(gen.result(), R"(#ifndef WGSL_SPEC_CONSTANT_23
 #define WGSL_SPEC_CONSTANT_23 3.0f
 #endif
@@ -56,7 +56,7 @@ TEST_F(GlslGeneratorImplTest_ModuleConstant, Emit_SpecConstant_NoConstructor) {
 
     GeneratorImpl& gen = Build();
 
-    ASSERT_TRUE(gen.EmitProgramConstVariable(var)) << gen.error();
+    ASSERT_TRUE(gen.EmitOverride(var)) << gen.error();
     EXPECT_EQ(gen.result(), R"(#ifndef WGSL_SPEC_CONSTANT_23
 #error spec constant required for constant id 23
 #endif
@@ -73,8 +73,8 @@ TEST_F(GlslGeneratorImplTest_ModuleConstant, Emit_SpecConstant_NoId) {
 
     GeneratorImpl& gen = Build();
 
-    ASSERT_TRUE(gen.EmitProgramConstVariable(a)) << gen.error();
+    ASSERT_TRUE(gen.EmitOverride(a)) << gen.error();
-    ASSERT_TRUE(gen.EmitProgramConstVariable(b)) << gen.error();
+    ASSERT_TRUE(gen.EmitOverride(b)) << gen.error();
     EXPECT_EQ(gen.result(), R"(#ifndef WGSL_SPEC_CONSTANT_0
 #define WGSL_SPEC_CONSTANT_0 3.0f
 #endif

src/tint/writer/hlsl/generator_impl.cc

@@ -365,7 +365,7 @@ bool GeneratorImpl::EmitDynamicVectorAssignment(const ast::AssignmentStatement*
                     out << "vec = (idx.xxxx == int4(0, 1, 2, 3)) ? val.xxxx : vec;";
                     break;
                 default:
-                    TINT_UNREACHABLE(Writer, builder_.Diagnostics())
+                    TINT_UNREACHABLE(Writer, diagnostics_)
                         << "invalid vector size " << vec->Width();
                     break;
             }
@@ -524,7 +524,7 @@ bool GeneratorImpl::EmitDynamicMatrixScalarAssignment(const ast::AssignmentState
                                         << vec_name << ";";
                                     break;
                                 default:
-                                    TINT_UNREACHABLE(Writer, builder_.Diagnostics())
+                                    TINT_UNREACHABLE(Writer, diagnostics_)
                                         << "invalid vector size " << vec->Width();
                                     break;
                             }
@@ -2861,41 +2861,46 @@ bool GeneratorImpl::EmitFunctionBodyWithDiscard(const ast::Function* func) {
 }
 
 bool GeneratorImpl::EmitGlobalVariable(const ast::Variable* global) {
-    if (global->is_const) {
+    return Switch(
-        return EmitProgramConstVariable(global);
+        global,  //
-    }
+        [&](const ast::Var* var) {
-
+            auto* sem = builder_.Sem().Get(global);
-    auto* sem = builder_.Sem().Get(global);
+            switch (sem->StorageClass()) {
-    switch (sem->StorageClass()) {
+                case ast::StorageClass::kUniform:
-        case ast::StorageClass::kUniform:
+                    return EmitUniformVariable(var, sem);
-            return EmitUniformVariable(sem);
+                case ast::StorageClass::kStorage:
-        case ast::StorageClass::kStorage:
+                    return EmitStorageVariable(var, sem);
-            return EmitStorageVariable(sem);
+                case ast::StorageClass::kHandle:
-        case ast::StorageClass::kHandle:
+                    return EmitHandleVariable(var, sem);
-            return EmitHandleVariable(sem);
+                case ast::StorageClass::kPrivate:
-        case ast::StorageClass::kPrivate:
+                    return EmitPrivateVariable(sem);
-            return EmitPrivateVariable(sem);
+                case ast::StorageClass::kWorkgroup:
-        case ast::StorageClass::kWorkgroup:
+                    return EmitWorkgroupVariable(sem);
-            return EmitWorkgroupVariable(sem);
+                default:
-        default:
+                    TINT_ICE(Writer, diagnostics_)
-            break;
+                        << "unhandled storage class " << sem->StorageClass();
-    }
+                    return false;
-
+            }
-    TINT_ICE(Writer, diagnostics_) << "unhandled storage class " << sem->StorageClass();
+        },
-    return false;
+        [&](const ast::Let* let) { return EmitProgramConstVariable(let); },
+        [&](const ast::Override* override) { return EmitOverride(override); },
+        [&](Default) {
+            TINT_ICE(Writer, diagnostics_)
+                << "unhandled global variable type " << global->TypeInfo().name;
+            return false;
+        });
 }
 
-bool GeneratorImpl::EmitUniformVariable(const sem::Variable* var) {
+bool GeneratorImpl::EmitUniformVariable(const ast::Var* var, const sem::Variable* sem) {
-    auto* decl = var->Declaration();
+    auto binding_point = var->BindingPoint();
-    auto binding_point = decl->BindingPoint();
+    auto* type = sem->Type()->UnwrapRef();
-    auto* type = var->Type()->UnwrapRef();
+    auto name = builder_.Symbols().NameFor(var->symbol);
-    auto name = builder_.Symbols().NameFor(decl->symbol);
     line() << "cbuffer cbuffer_" << name << RegisterAndSpace('b', binding_point) << " {";
 
     {
         ScopedIndent si(this);
         auto out = line();
-        if (!EmitTypeAndName(out, type, ast::StorageClass::kUniform, var->Access(), name)) {
+        if (!EmitTypeAndName(out, type, ast::StorageClass::kUniform, sem->Access(), name)) {
             return false;
         }
         out << ";";
@@ -2906,29 +2911,27 @@ bool GeneratorImpl::EmitUniformVariable(const sem::Variable* var) {
     return true;
 }
 
-bool GeneratorImpl::EmitStorageVariable(const sem::Variable* var) {
+bool GeneratorImpl::EmitStorageVariable(const ast::Var* var, const sem::Variable* sem) {
-    auto* decl = var->Declaration();
+    auto* type = sem->Type()->UnwrapRef();
-    auto* type = var->Type()->UnwrapRef();
     auto out = line();
-    if (!EmitTypeAndName(out, type, ast::StorageClass::kStorage, var->Access(),
+    if (!EmitTypeAndName(out, type, ast::StorageClass::kStorage, sem->Access(),
-                         builder_.Symbols().NameFor(decl->symbol))) {
+                         builder_.Symbols().NameFor(var->symbol))) {
         return false;
     }
 
-    out << RegisterAndSpace(var->Access() == ast::Access::kRead ? 't' : 'u', decl->BindingPoint())
+    out << RegisterAndSpace(sem->Access() == ast::Access::kRead ? 't' : 'u', var->BindingPoint())
         << ";";
 
     return true;
 }
 
-bool GeneratorImpl::EmitHandleVariable(const sem::Variable* var) {
+bool GeneratorImpl::EmitHandleVariable(const ast::Var* var, const sem::Variable* sem) {
-    auto* decl = var->Declaration();
+    auto* unwrapped_type = sem->Type()->UnwrapRef();
-    auto* unwrapped_type = var->Type()->UnwrapRef();
     auto out = line();
 
-    auto name = builder_.Symbols().NameFor(decl->symbol);
+    auto name = builder_.Symbols().NameFor(var->symbol);
-    auto* type = var->Type()->UnwrapRef();
+    auto* type = sem->Type()->UnwrapRef();
-    if (!EmitTypeAndName(out, type, var->StorageClass(), var->Access(), name)) {
+    if (!EmitTypeAndName(out, type, sem->StorageClass(), sem->Access(), name)) {
         return false;
     }
 
@@ -2944,7 +2947,7 @@ bool GeneratorImpl::EmitHandleVariable(const sem::Variable* var) {
     }
 
     if (register_space) {
-        auto bp = decl->BindingPoint();
+        auto bp = var->BindingPoint();
         out << " : register(" << register_space << bp.binding->value << ", space" << bp.group->value
             << ")";
     }
@@ -3078,8 +3081,8 @@ bool GeneratorImpl::EmitEntryPointFunction(const ast::Function* func) {
                 if (wgsize[i].overridable_const) {
                     auto* global =
                         builder_.Sem().Get<sem::GlobalVariable>(wgsize[i].overridable_const);
-                    if (!global->IsOverridable()) {
+                    if (!global->Declaration()->Is<ast::Override>()) {
-                        TINT_ICE(Writer, builder_.Diagnostics())
+                        TINT_ICE(Writer, diagnostics_)
                             << "expected a pipeline-overridable constant";
                     }
                     out << kSpecConstantPrefix << global->ConstantId();
@@ -3611,7 +3614,15 @@ bool GeneratorImpl::EmitStatement(const ast::Statement* stmt) {
             return EmitSwitch(s);
         },
         [&](const ast::VariableDeclStatement* v) {  //
-            return EmitVariable(v->variable);
+            return Switch(
+                v->variable,  //
+                [&](const ast::Var* var) { return EmitVar(var); },
+                [&](const ast::Let* let) { return EmitLet(let); },
+                [&](Default) {  //
+                    TINT_ICE(Writer, diagnostics_)
+                        << "unknown variable type: " << v->variable->TypeInfo().name;
+                    return false;
+                });
         },
         [&](Default) {  //
             diagnostics_.add_error(diag::System::Writer,
@@ -4018,20 +4029,11 @@ bool GeneratorImpl::EmitUnaryOp(std::ostream& out, const ast::UnaryOpExpression*
     return true;
 }
 
-bool GeneratorImpl::EmitVariable(const ast::Variable* var) {
+bool GeneratorImpl::EmitVar(const ast::Var* var) {
     auto* sem = builder_.Sem().Get(var);
     auto* type = sem->Type()->UnwrapRef();
 
-    // TODO(dsinclair): Handle variable attributes
-    if (!var->attributes.empty()) {
-        diagnostics_.add_error(diag::System::Writer, "Variable attributes are not handled yet");
-        return false;
-    }
-
     auto out = line();
-    if (var->is_const) {
-        out << "const ";
-    }
     if (!EmitTypeAndName(out, type, sem->StorageClass(), sem->Access(),
                          builder_.Symbols().NameFor(var->symbol))) {
         return false;
@@ -4053,60 +4055,71 @@ bool GeneratorImpl::EmitVariable(const ast::Variable* var) {
     return true;
 }
 
-bool GeneratorImpl::EmitProgramConstVariable(const ast::Variable* var) {
+bool GeneratorImpl::EmitLet(const ast::Let* let) {
-    for (auto* d : var->attributes) {
+    auto* sem = builder_.Sem().Get(let);
-        if (!d->Is<ast::IdAttribute>()) {
+    auto* type = sem->Type()->UnwrapRef();
-            diagnostics_.add_error(diag::System::Writer, "Decorated const values not valid");
+
-            return false;
+    auto out = line();
-        }
+    out << "const ";
-    }
+    if (!EmitTypeAndName(out, type, ast::StorageClass::kNone, ast::Access::kUndefined,
-    if (!var->is_const) {
+                         builder_.Symbols().NameFor(let->symbol))) {
-        diagnostics_.add_error(diag::System::Writer, "Expected a const value");
         return false;
     }
+    out << " = ";
+    if (!EmitExpression(out, let->constructor)) {
+        return false;
+    }
+    out << ";";
 
-    auto* sem = builder_.Sem().Get(var);
+    return true;
+}
+
+bool GeneratorImpl::EmitProgramConstVariable(const ast::Let* let) {
+    auto* sem = builder_.Sem().Get(let);
     auto* type = sem->Type();
 
-    auto* global = sem->As<sem::GlobalVariable>();
+    auto out = line();
-    if (global && global->IsOverridable()) {
+    out << "static const ";
-        auto const_id = global->ConstantId();
+    if (!EmitTypeAndName(out, type, ast::StorageClass::kNone, ast::Access::kUndefined,
+                         builder_.Symbols().NameFor(let->symbol))) {
+        return false;
+    }
+    out << " = ";
+    if (!EmitExpression(out, let->constructor)) {
+        return false;
+    }
+    out << ";";
 
-        line() << "#ifndef " << kSpecConstantPrefix << const_id;
+    return true;
+}
 
-        if (var->constructor != nullptr) {
+bool GeneratorImpl::EmitOverride(const ast::Override* override) {
-            auto out = line();
+    auto* sem = builder_.Sem().Get(override);
-            out << "#define " << kSpecConstantPrefix << const_id << " ";
+    auto* type = sem->Type();
-            if (!EmitExpression(out, var->constructor)) {
+
-                return false;
+    auto const_id = sem->ConstantId();
-            }
+
-        } else {
+    line() << "#ifndef " << kSpecConstantPrefix << const_id;
-            line() << "#error spec constant required for constant id " << const_id;
+
-        }
+    if (override->constructor != nullptr) {
-        line() << "#endif";
+        auto out = line();
-        {
+        out << "#define " << kSpecConstantPrefix << const_id << " ";
-            auto out = line();
+        if (!EmitExpression(out, override->constructor)) {
-            out << "static const ";
+            return false;
-            if (!EmitTypeAndName(out, type, sem->StorageClass(), sem->Access(),
-                                 builder_.Symbols().NameFor(var->symbol))) {
-                return false;
-            }
-            out << " = " << kSpecConstantPrefix << const_id << ";";
         }
     } else {
+        line() << "#error spec constant required for constant id " << const_id;
+    }
+    line() << "#endif";
+    {
         auto out = line();
         out << "static const ";
         if (!EmitTypeAndName(out, type, sem->StorageClass(), sem->Access(),
-                             builder_.Symbols().NameFor(var->symbol))) {
+                             builder_.Symbols().NameFor(override->symbol))) {
             return false;
         }
-        out << " = ";
+        out << " = " << kSpecConstantPrefix << const_id << ";";
-        if (!EmitExpression(out, var->constructor)) {
-            return false;
-        }
-        out << ";";
     }
-
     return true;
 }
 

src/tint/writer/hlsl/generator_impl.h

@@ -303,19 +303,22 @@ class GeneratorImpl : public TextGenerator {
     bool EmitGlobalVariable(const ast::Variable* global);
 
     /// Handles emitting a global variable with the uniform storage class
-    /// @param var the global variable
+    /// @param var the AST node for the 'var'
+    /// @param sem the semantic node for the 'var'
     /// @returns true on success
-    bool EmitUniformVariable(const sem::Variable* var);
+    bool EmitUniformVariable(const ast::Var* var, const sem::Variable* sem);
 
     /// Handles emitting a global variable with the storage storage class
-    /// @param var the global variable
+    /// @param var the AST node for the 'var'
+    /// @param sem the semantic node for the 'var'
     /// @returns true on success
-    bool EmitStorageVariable(const sem::Variable* var);
+    bool EmitStorageVariable(const ast::Var* var, const sem::Variable* sem);
 
     /// Handles emitting a global variable with the handle storage class
-    /// @param var the global variable
+    /// @param var the AST node for the 'var'
+    /// @param sem the semantic node for the 'var'
     /// @returns true on success
-    bool EmitHandleVariable(const sem::Variable* var);
+    bool EmitHandleVariable(const ast::Var* var, const sem::Variable* sem);
 
     /// Handles emitting a global variable with the private storage class
     /// @param var the global variable
@@ -437,14 +440,22 @@ class GeneratorImpl : public TextGenerator {
     /// @param type the type to emit the value for
     /// @returns true if the zero value was successfully emitted.
     bool EmitZeroValue(std::ostream& out, const sem::Type* type);
-    /// Handles generating a variable
+    /// Handles generating a 'var' declaration
     /// @param var the variable to generate
     /// @returns true if the variable was emitted
-    bool EmitVariable(const ast::Variable* var);
+    bool EmitVar(const ast::Var* var);
-    /// Handles generating a program scope constant variable
+    /// Handles generating a function-scope 'let' declaration
-    /// @param var the variable to emit
+    /// @param let the variable to generate
     /// @returns true if the variable was emitted
-    bool EmitProgramConstVariable(const ast::Variable* var);
+    bool EmitLet(const ast::Let* let);
+    /// Handles generating a module-scope 'let' declaration
+    /// @param let the 'let' to emit
+    /// @returns true if the variable was emitted
+    bool EmitProgramConstVariable(const ast::Let* let);
+    /// Handles generating a module-scope 'override' declaration
+    /// @param override the 'override' to emit
+    /// @returns true if the variable was emitted
+    bool EmitOverride(const ast::Override* override);
     /// Emits call to a helper vector assignment function for the input assignment
     /// statement and vector type. This is used to work around FXC issues where
     /// assignments to vectors with dynamic indices cause compilation failures.

src/tint/writer/hlsl/generator_impl_module_constant_test.cc

@@ -40,7 +40,7 @@ TEST_F(HlslGeneratorImplTest_ModuleConstant, Emit_SpecConstant) {
 
     GeneratorImpl& gen = Build();
 
-    ASSERT_TRUE(gen.EmitProgramConstVariable(var)) << gen.error();
+    ASSERT_TRUE(gen.EmitOverride(var)) << gen.error();
     EXPECT_EQ(gen.result(), R"(#ifndef WGSL_SPEC_CONSTANT_23
 #define WGSL_SPEC_CONSTANT_23 3.0f
 #endif
@@ -56,7 +56,7 @@ TEST_F(HlslGeneratorImplTest_ModuleConstant, Emit_SpecConstant_NoConstructor) {
 
     GeneratorImpl& gen = Build();
 
-    ASSERT_TRUE(gen.EmitProgramConstVariable(var)) << gen.error();
+    ASSERT_TRUE(gen.EmitOverride(var)) << gen.error();
     EXPECT_EQ(gen.result(), R"(#ifndef WGSL_SPEC_CONSTANT_23
 #error spec constant required for constant id 23
 #endif
@@ -73,8 +73,8 @@ TEST_F(HlslGeneratorImplTest_ModuleConstant, Emit_SpecConstant_NoId) {
 
     GeneratorImpl& gen = Build();
 
-    ASSERT_TRUE(gen.EmitProgramConstVariable(a)) << gen.error();
+    ASSERT_TRUE(gen.EmitOverride(a)) << gen.error();
-    ASSERT_TRUE(gen.EmitProgramConstVariable(b)) << gen.error();
+    ASSERT_TRUE(gen.EmitOverride(b)) << gen.error();
     EXPECT_EQ(gen.result(), R"(#ifndef WGSL_SPEC_CONSTANT_0
 #define WGSL_SPEC_CONSTANT_0 3.0f
 #endif

src/tint/writer/msl/generator_impl.cc

@@ -253,16 +253,13 @@ bool GeneratorImpl::Generate() {
             [&](const ast::Alias*) {
                 return true;  // folded away by the writer
             },
-            [&](const ast::Variable* var) {
+            [&](const ast::Let* let) {
-                if (var->is_const) {
+                TINT_DEFER(line());
-                    TINT_DEFER(line());
+                return EmitProgramConstVariable(let);
-                    return EmitProgramConstVariable(var);
+            },
-                }
+            [&](const ast::Override* override) {
-                // These are pushed into the entry point by sanitizer transforms.
+                TINT_DEFER(line());
-                TINT_ICE(Writer, diagnostics_)
+                return EmitOverride(override);
-                    << "module-scope variables should have been handled by the MSL "
-                       "sanitizer";
-                return false;
             },
             [&](const ast::Function* func) {
                 TINT_DEFER(line());
@@ -1866,8 +1863,8 @@ bool GeneratorImpl::EmitEntryPointFunction(const ast::Function* func) {
     // Returns the binding index of a variable, requiring that the group
     // attribute have a value of zero.
     const uint32_t kInvalidBindingIndex = std::numeric_limits<uint32_t>::max();
-    auto get_binding_index = [&](const ast::Variable* var) -> uint32_t {
+    auto get_binding_index = [&](const ast::Parameter* param) -> uint32_t {
-        auto bp = var->BindingPoint();
+        auto bp = param->BindingPoint();
         if (bp.group == nullptr || bp.binding == nullptr) {
             TINT_ICE(Writer, diagnostics_)
                 << "missing binding attributes for entry point parameter";
@@ -1890,15 +1887,15 @@ bool GeneratorImpl::EmitEntryPointFunction(const ast::Function* func) {
 
         // Emit entry point parameters.
         bool first = true;
-        for (auto* var : func->params) {
+        for (auto* param : func->params) {
             if (!first) {
                 out << ", ";
             }
             first = false;
 
-            auto* type = program_->Sem().Get(var)->Type()->UnwrapRef();
+            auto* type = program_->Sem().Get(param)->Type()->UnwrapRef();
 
-            auto param_name = program_->Symbols().NameFor(var->symbol);
+            auto param_name = program_->Symbols().NameFor(param->symbol);
             if (!EmitType(out, type, param_name)) {
                 return false;
             }
@@ -1910,26 +1907,26 @@ bool GeneratorImpl::EmitEntryPointFunction(const ast::Function* func) {
             if (type->Is<sem::Struct>()) {
                 out << " [[stage_in]]";
             } else if (type->is_handle()) {
-                uint32_t binding = get_binding_index(var);
+                uint32_t binding = get_binding_index(param);
                 if (binding == kInvalidBindingIndex) {
                     return false;
                 }
-                if (var->type->Is<ast::Sampler>()) {
+                if (param->type->Is<ast::Sampler>()) {
                     out << " [[sampler(" << binding << ")]]";
-                } else if (var->type->Is<ast::Texture>()) {
+                } else if (param->type->Is<ast::Texture>()) {
                     out << " [[texture(" << binding << ")]]";
                 } else {
                     TINT_ICE(Writer, diagnostics_) << "invalid handle type entry point parameter";
                     return false;
                 }
-            } else if (auto* ptr = var->type->As<ast::Pointer>()) {
+            } else if (auto* ptr = param->type->As<ast::Pointer>()) {
                 auto sc = ptr->storage_class;
                 if (sc == ast::StorageClass::kWorkgroup) {
                     auto& allocations = workgroup_allocations_[func_name];
                     out << " [[threadgroup(" << allocations.size() << ")]]";
                     allocations.push_back(program_->Sem().Get(ptr->type)->Size());
                 } else if (sc == ast::StorageClass::kStorage || sc == ast::StorageClass::kUniform) {
-                    uint32_t binding = get_binding_index(var);
+                    uint32_t binding = get_binding_index(param);
                     if (binding == kInvalidBindingIndex) {
                         return false;
                     }
@@ -1940,7 +1937,7 @@ bool GeneratorImpl::EmitEntryPointFunction(const ast::Function* func) {
                     return false;
                 }
             } else {
-                auto& attrs = var->attributes;
+                auto& attrs = param->attributes;
                 bool builtin_found = false;
                 for (auto* attr : attrs) {
                     auto* builtin = attr->As<ast::BuiltinAttribute>();
@@ -2340,8 +2337,15 @@ bool GeneratorImpl::EmitStatement(const ast::Statement* stmt) {
             return EmitSwitch(s);
         },
         [&](const ast::VariableDeclStatement* v) {  //
-            auto* var = program_->Sem().Get(v->variable);
+            return Switch(
-            return EmitVariable(var);
+                v->variable,  //
+                [&](const ast::Var* var) { return EmitVar(var); },
+                [&](const ast::Let* let) { return EmitLet(let); },
+                [&](Default) {  //
+                    TINT_ICE(Writer, diagnostics_)
+                        << "unknown statement type: " << stmt->TypeInfo().name;
+                    return false;
+                });
         },
         [&](Default) {
             diagnostics_.add_error(diag::System::Writer,
@@ -2918,19 +2922,13 @@ bool GeneratorImpl::EmitUnaryOp(std::ostream& out, const ast::UnaryOpExpression*
     return true;
 }
 
-bool GeneratorImpl::EmitVariable(const sem::Variable* var) {
+bool GeneratorImpl::EmitVar(const ast::Var* var) {
-    auto* decl = var->Declaration();
+    auto* sem = program_->Sem().Get(var);
-
+    auto* type = sem->Type()->UnwrapRef();
-    for (auto* attr : decl->attributes) {
-        if (!attr->Is<ast::InternalAttribute>()) {
-            TINT_ICE(Writer, diagnostics_) << "unexpected variable attribute";
-            return false;
-        }
-    }
 
     auto out = line();
 
-    switch (var->StorageClass()) {
+    switch (sem->StorageClass()) {
         case ast::StorageClass::kFunction:
         case ast::StorageClass::kHandle:
         case ast::StorageClass::kNone:
@@ -2946,12 +2944,7 @@ bool GeneratorImpl::EmitVariable(const sem::Variable* var) {
             return false;
     }
 
-    auto* type = var->Type()->UnwrapRef();
+    std::string name = program_->Symbols().NameFor(var->symbol);
-
-    std::string name = program_->Symbols().NameFor(decl->symbol);
-    if (decl->is_const) {
-        name = "const " + name;
-    }
     if (!EmitType(out, type, name)) {
         return false;
     }
@@ -2960,14 +2953,14 @@ bool GeneratorImpl::EmitVariable(const sem::Variable* var) {
         out << " " << name;
     }
 
-    if (decl->constructor != nullptr) {
+    if (var->constructor != nullptr) {
         out << " = ";
-        if (!EmitExpression(out, decl->constructor)) {
+        if (!EmitExpression(out, var->constructor)) {
             return false;
         }
-    } else if (var->StorageClass() == ast::StorageClass::kPrivate ||
+    } else if (sem->StorageClass() == ast::StorageClass::kPrivate ||
-               var->StorageClass() == ast::StorageClass::kFunction ||
+               sem->StorageClass() == ast::StorageClass::kFunction ||
-               var->StorageClass() == ast::StorageClass::kNone) {
+               sem->StorageClass() == ast::StorageClass::kNone) {
         out << " = ";
         if (!EmitZeroValue(out, type)) {
             return false;
@@ -2978,34 +2971,63 @@ bool GeneratorImpl::EmitVariable(const sem::Variable* var) {
     return true;
 }
 
-bool GeneratorImpl::EmitProgramConstVariable(const ast::Variable* var) {
+bool GeneratorImpl::EmitLet(const ast::Let* let) {
-    for (auto* d : var->attributes) {
+    auto* sem = program_->Sem().Get(let);
-        if (!d->Is<ast::IdAttribute>()) {
+    auto* type = sem->Type();
-            diagnostics_.add_error(diag::System::Writer, "Decorated const values not valid");
+
+    auto out = line();
+
+    switch (sem->StorageClass()) {
+        case ast::StorageClass::kFunction:
+        case ast::StorageClass::kHandle:
+        case ast::StorageClass::kNone:
+            break;
+        case ast::StorageClass::kPrivate:
+            out << "thread ";
+            break;
+        case ast::StorageClass::kWorkgroup:
+            out << "threadgroup ";
+            break;
+        default:
+            TINT_ICE(Writer, diagnostics_) << "unhandled variable storage class";
             return false;
-        }
     }
-    if (!var->is_const) {
+
-        diagnostics_.add_error(diag::System::Writer, "Expected a const value");
+    std::string name = "const " + program_->Symbols().NameFor(let->symbol);
+    if (!EmitType(out, type, name)) {
         return false;
     }
 
+    // Variable name is output as part of the type for arrays and pointers.
+    if (!type->Is<sem::Array>() && !type->Is<sem::Pointer>()) {
+        out << " " << name;
+    }
+
+    out << " = ";
+    if (!EmitExpression(out, let->constructor)) {
+        return false;
+    }
+    out << ";";
+
+    return true;
+}
+
+bool GeneratorImpl::EmitProgramConstVariable(const ast::Let* let) {
+    auto* global = program_->Sem().Get<sem::GlobalVariable>(let);
+    auto* type = global->Type();
+
     auto out = line();
     out << "constant ";
-    auto* type = program_->Sem().Get(var)->Type()->UnwrapRef();
+    if (!EmitType(out, type, program_->Symbols().NameFor(let->symbol))) {
-    if (!EmitType(out, type, program_->Symbols().NameFor(var->symbol))) {
         return false;
     }
     if (!type->Is<sem::Array>()) {
-        out << " " << program_->Symbols().NameFor(var->symbol);
+        out << " " << program_->Symbols().NameFor(let->symbol);
     }
 
-    auto* global = program_->Sem().Get<sem::GlobalVariable>(var);
+    if (let->constructor != nullptr) {
-    if (global && global->IsOverridable()) {
-        out << " [[function_constant(" << global->ConstantId() << ")]]";
-    } else if (var->constructor != nullptr) {
         out << " = ";
-        if (!EmitExpression(out, var->constructor)) {
+        if (!EmitExpression(out, let->constructor)) {
             return false;
         }
     }
@@ -3014,6 +3036,24 @@ bool GeneratorImpl::EmitProgramConstVariable(const ast::Variable* var) {
     return true;
 }
 
+bool GeneratorImpl::EmitOverride(const ast::Override* override) {
+    auto* global = program_->Sem().Get<sem::GlobalVariable>(override);
+    auto* type = global->Type();
+
+    auto out = line();
+    out << "constant ";
+    if (!EmitType(out, type, program_->Symbols().NameFor(override->symbol))) {
+        return false;
+    }
+    if (!type->Is<sem::Array>()) {
+        out << " " << program_->Symbols().NameFor(override->symbol);
+    }
+
+    out << " [[function_constant(" << global->ConstantId() << ")]];";
+
+    return true;
+}
+
 GeneratorImpl::SizeAndAlign GeneratorImpl::MslPackedTypeSizeAndAlign(const sem::Type* ty) {
     return Switch(
         ty,

src/tint/writer/msl/generator_impl.h

@@ -348,14 +348,22 @@ class GeneratorImpl : public TextGenerator {
     /// @param expr the expression to emit
     /// @returns true if the expression was emitted
     bool EmitUnaryOp(std::ostream& out, const ast::UnaryOpExpression* expr);
-    /// Handles generating a variable
+    /// Handles generating a 'var' declaration
     /// @param var the variable to generate
     /// @returns true if the variable was emitted
-    bool EmitVariable(const sem::Variable* var);
+    bool EmitVar(const ast::Var* var);
-    /// Handles generating a program scope constant variable
+    /// Handles generating a function-scope 'let' declaration
-    /// @param var the variable to emit
+    /// @param let the variable to generate
     /// @returns true if the variable was emitted
-    bool EmitProgramConstVariable(const ast::Variable* var);
+    bool EmitLet(const ast::Let* let);
+    /// Handles generating a module-scope 'let' declaration
+    /// @param let the 'let' to emit
+    /// @returns true if the variable was emitted
+    bool EmitProgramConstVariable(const ast::Let* let);
+    /// Handles generating a module-scope 'override' declaration
+    /// @param override the 'override' to emit
+    /// @returns true if the variable was emitted
+    bool EmitOverride(const ast::Override* override);
     /// Emits the zero value for the given type
     /// @param out the output of the expression stream
     /// @param type the type to emit the value for

src/tint/writer/msl/generator_impl_module_constant_test.cc

@@ -39,7 +39,7 @@ TEST_F(MslGeneratorImplTest, Emit_SpecConstant) {
 
     GeneratorImpl& gen = Build();
 
-    ASSERT_TRUE(gen.EmitProgramConstVariable(var)) << gen.error();
+    ASSERT_TRUE(gen.EmitOverride(var)) << gen.error();
     EXPECT_EQ(gen.result(), "constant float pos [[function_constant(23)]];\n");
 }
 
@@ -52,8 +52,8 @@ TEST_F(MslGeneratorImplTest, Emit_SpecConstant_NoId) {
 
     GeneratorImpl& gen = Build();
 
-    ASSERT_TRUE(gen.EmitProgramConstVariable(var_a)) << gen.error();
+    ASSERT_TRUE(gen.EmitOverride(var_a)) << gen.error();
-    ASSERT_TRUE(gen.EmitProgramConstVariable(var_b)) << gen.error();
+    ASSERT_TRUE(gen.EmitOverride(var_b)) << gen.error();
     EXPECT_EQ(gen.result(), R"(constant float a [[function_constant(0)]];
 constant float b [[function_constant(1)]];
 )");

src/tint/writer/spirv/builder.cc

@@ -533,7 +533,7 @@ bool Builder::GenerateExecutionModes(const ast::Function* func, uint32_t id) {
                     // Make the constant specializable.
                     auto* sem_const =
                         builder_.Sem().Get<sem::GlobalVariable>(wgsize[i].overridable_const);
-                    if (!sem_const->IsOverridable()) {
+                    if (!sem_const->Declaration()->Is<ast::Override>()) {
                         TINT_ICE(Writer, builder_.Diagnostics())
                             << "expected a pipeline-overridable constant";
                     }
@@ -692,19 +692,19 @@ uint32_t Builder::GenerateFunctionTypeIfNeeded(const sem::Function* func) {
     });
 }
 
-bool Builder::GenerateFunctionVariable(const ast::Variable* var) {
+bool Builder::GenerateFunctionVariable(const ast::Variable* v) {
     uint32_t init_id = 0;
-    if (var->constructor) {
+    if (v->constructor) {
-        init_id = GenerateExpressionWithLoadIfNeeded(var->constructor);
+        init_id = GenerateExpressionWithLoadIfNeeded(v->constructor);
         if (init_id == 0) {
             return false;
         }
     }
 
-    auto* sem = builder_.Sem().Get(var);
+    auto* sem = builder_.Sem().Get(v);
 
-    if (var->is_const) {
+    if (auto* let = v->As<ast::Let>()) {
-        if (!var->constructor) {
+        if (!let->constructor) {
             error_ = "missing constructor for constant";
             return false;
         }
@@ -721,8 +721,7 @@ bool Builder::GenerateFunctionVariable(const ast::Variable* var) {
         return false;
     }
 
-    push_debug(spv::Op::OpName,
+    push_debug(spv::Op::OpName, {Operand(var_id), Operand(builder_.Symbols().NameFor(v->symbol))});
-               {Operand(var_id), Operand(builder_.Symbols().NameFor(var->symbol))});
 
     // TODO(dsinclair) We could detect if the constructor is fully const and emit
     // an initializer value for the variable instead of doing the OpLoad.
@@ -733,7 +732,7 @@ bool Builder::GenerateFunctionVariable(const ast::Variable* var) {
     push_function_var(
         {Operand(type_id), result, U32Operand(ConvertStorageClass(sc)), Operand(null_id)});
 
-    if (var->constructor) {
+    if (v->constructor) {
         if (!GenerateStore(var_id, init_id)) {
             return false;
         }
@@ -748,66 +747,61 @@ bool Builder::GenerateStore(uint32_t to, uint32_t from) {
     return push_function_inst(spv::Op::OpStore, {Operand(to), Operand(from)});
 }
 
-bool Builder::GenerateGlobalVariable(const ast::Variable* var) {
+bool Builder::GenerateGlobalVariable(const ast::Variable* v) {
-    auto* sem = builder_.Sem().Get(var);
+    auto* sem = builder_.Sem().Get(v);
     auto* type = sem->Type()->UnwrapRef();
 
     uint32_t init_id = 0;
-    if (var->constructor) {
+    if (auto* ctor = v->constructor) {
-        if (!var->is_overridable) {
+        if (!v->Is<ast::Override>()) {
-            auto* ctor = builder_.Sem().Get(var->constructor);
+            auto* ctor_sem = builder_.Sem().Get(ctor);
-            if (auto constant = ctor->ConstantValue()) {
+            if (auto constant = ctor_sem->ConstantValue()) {
                 init_id = GenerateConstantIfNeeded(std::move(constant));
             }
         }
         if (init_id == 0) {
-            init_id = GenerateConstructorExpression(var, var->constructor);
+            init_id = GenerateConstructorExpression(v, v->constructor);
         }
         if (init_id == 0) {
             return false;
         }
     }
 
-    if (var->is_const) {
+    if (auto* override = v->As<ast::Override>(); override && !override->constructor) {
-        if (!var->constructor) {
+        // SPIR-V requires specialization constants to have initializers.
-            // Constants must have an initializer unless they are overridable.
+        init_id = Switch(
-            if (!var->is_overridable) {
+            type,  //
-                error_ = "missing constructor for constant";
+            [&](const sem::F32*) {
-                return false;
+                ast::FloatLiteralExpression l(ProgramID{}, Source{}, 0,
-            }
+                                              ast::FloatLiteralExpression::Suffix::kF);
-
+                return GenerateLiteralIfNeeded(override, &l);
-            // SPIR-V requires specialization constants to have initializers.
+            },
-            init_id = Switch(
+            [&](const sem::U32*) {
-                type,  //
+                ast::IntLiteralExpression l(ProgramID{}, Source{}, 0,
-                [&](const sem::F32*) {
+                                            ast::IntLiteralExpression::Suffix::kU);
-                    ast::FloatLiteralExpression l(ProgramID{}, Source{}, 0,
+                return GenerateLiteralIfNeeded(override, &l);
-                                                  ast::FloatLiteralExpression::Suffix::kF);
+            },
-                    return GenerateLiteralIfNeeded(var, &l);
+            [&](const sem::I32*) {
-                },
+                ast::IntLiteralExpression l(ProgramID{}, Source{}, 0,
-                [&](const sem::U32*) {
+                                            ast::IntLiteralExpression::Suffix::kI);
-                    ast::IntLiteralExpression l(ProgramID{}, Source{}, 0,
+                return GenerateLiteralIfNeeded(override, &l);
-                                                ast::IntLiteralExpression::Suffix::kU);
+            },
-                    return GenerateLiteralIfNeeded(var, &l);
+            [&](const sem::Bool*) {
-                },
+                ast::BoolLiteralExpression l(ProgramID{}, Source{}, false);
-                [&](const sem::I32*) {
+                return GenerateLiteralIfNeeded(override, &l);
-                    ast::IntLiteralExpression l(ProgramID{}, Source{}, 0,
+            },
-                                                ast::IntLiteralExpression::Suffix::kI);
+            [&](Default) {
-                    return GenerateLiteralIfNeeded(var, &l);
+                error_ = "invalid type for pipeline constant ID, must be scalar";
-                },
-                [&](const sem::Bool*) {
-                    ast::BoolLiteralExpression l(ProgramID{}, Source{}, false);
-                    return GenerateLiteralIfNeeded(var, &l);
-                },
-                [&](Default) {
-                    error_ = "invalid type for pipeline constant ID, must be scalar";
-                    return 0;
-                });
-            if (init_id == 0) {
                 return 0;
-            }
+            });
+        if (init_id == 0) {
+            return 0;
         }
+    }
+
+    if (v->IsAnyOf<ast::Let, ast::Override>()) {
         push_debug(spv::Op::OpName,
-                   {Operand(init_id), Operand(builder_.Symbols().NameFor(var->symbol))});
+                   {Operand(init_id), Operand(builder_.Symbols().NameFor(v->symbol))});
 
         RegisterVariable(sem, init_id);
         return true;
@@ -824,12 +818,11 @@ bool Builder::GenerateGlobalVariable(const ast::Variable* var) {
         return false;
     }
 
-    push_debug(spv::Op::OpName,
+    push_debug(spv::Op::OpName, {Operand(var_id), Operand(builder_.Symbols().NameFor(v->symbol))});
-               {Operand(var_id), Operand(builder_.Symbols().NameFor(var->symbol))});
 
     OperandList ops = {Operand(type_id), result, U32Operand(ConvertStorageClass(sc))};
 
-    if (var->constructor) {
+    if (v->constructor) {
         ops.push_back(Operand(init_id));
     } else {
         auto* st = type->As<sem::StorageTexture>();
@@ -871,7 +864,7 @@ bool Builder::GenerateGlobalVariable(const ast::Variable* var) {
 
     push_type(spv::Op::OpVariable, std::move(ops));
 
-    for (auto* attr : var->attributes) {
+    for (auto* attr : v->attributes) {
         bool ok = Switch(
             attr,
             [&](const ast::BuiltinAttribute* builtin) {
@@ -1332,7 +1325,7 @@ uint32_t Builder::GenerateTypeConstructorOrConversion(const sem::Call* call,
 
     // Generate the zero initializer if there are no values provided.
     if (args.empty()) {
-        if (global_var && global_var->IsOverridable()) {
+        if (global_var && global_var->Declaration()->Is<ast::Override>()) {
             auto constant_id = global_var->ConstantId();
             if (result_type->Is<sem::I32>()) {
                 return GenerateConstantIfNeeded(ScalarConstant::I32(0).AsSpecOp(constant_id));
@@ -1637,7 +1630,7 @@ uint32_t Builder::GenerateLiteralIfNeeded(const ast::Variable* var,
     ScalarConstant constant;
 
     auto* global = builder_.Sem().Get<sem::GlobalVariable>(var);
-    if (global && global->IsOverridable()) {
+    if (global && global->Declaration()->Is<ast::Override>()) {
         constant.is_spec_op = true;
         constant.constant_id = global->ConstantId();
     }

src/tint/writer/wgsl/generator_impl.cc

@@ -635,46 +635,60 @@ bool GeneratorImpl::EmitStructType(const ast::Struct* str) {
     return true;
 }
 
-bool GeneratorImpl::EmitVariable(std::ostream& out, const ast::Variable* var) {
+bool GeneratorImpl::EmitVariable(std::ostream& out, const ast::Variable* v) {
-    if (!var->attributes.empty()) {
+    if (!v->attributes.empty()) {
-        if (!EmitAttributes(out, var->attributes)) {
+        if (!EmitAttributes(out, v->attributes)) {
             return false;
         }
         out << " ";
     }
 
-    if (var->is_overridable) {
+    bool ok = Switch(
-        out << "override";
+        v,  //
-    } else if (var->is_const) {
+        [&](const ast::Let* ) {
-        out << "let";
+            out << "let";
-    } else {
+            return true;
-        out << "var";
+        },
-        auto sc = var->declared_storage_class;
+        [&](const ast::Override* ) {
-        auto ac = var->declared_access;
+            out << "override";
-        if (sc != ast::StorageClass::kNone || ac != ast::Access::kUndefined) {
+            return true;
-            out << "<" << sc;
+        },
-            if (ac != ast::Access::kUndefined) {
+        [&](const ast::Var* var) {
-                out << ", ";
+            out << "var";
-                if (!EmitAccess(out, ac)) {
+            auto sc = var->declared_storage_class;
-                    return false;
+            auto ac = var->declared_access;
+            if (sc != ast::StorageClass::kNone || ac != ast::Access::kUndefined) {
+                out << "<" << sc;
+                if (ac != ast::Access::kUndefined) {
+                    out << ", ";
+                    if (!EmitAccess(out, ac)) {
+                        return false;
+                    }
                 }
+                out << ">";
             }
-            out << ">";
+            return true;
-        }
+        },
+        [&](Default) {
+            TINT_ICE(Writer, diagnostics_) << "unhandled variable type " << v->TypeInfo().name;
+            return false;
+        });
+    if (!ok) {
+        return false;
     }
 
-    out << " " << program_->Symbols().NameFor(var->symbol);
+    out << " " << program_->Symbols().NameFor(v->symbol);
 
-    if (auto* ty = var->type) {
+    if (auto* ty = v->type) {
         out << " : ";
         if (!EmitType(out, ty)) {
             return false;
         }
     }
 
-    if (var->constructor != nullptr) {
+    if (v->constructor != nullptr) {
         out << " = ";
-        if (!EmitExpression(out, var->constructor)) {
+        if (!EmitExpression(out, v->constructor)) {
             return false;
         }
     }

test/tint/bug/tint/827.wgsl.expected.hlsl

@@ -1,4 +1,5 @@
 static const uint width = 128u;
+
 Texture2D tex : register(t0, space0);
 RWByteAddressBuffer result : register(u1, space0);
 

test/tint/bug/tint/914.wgsl.expected.hlsl

@@ -45,6 +45,7 @@ static const uint ColPerThread = 4u;
 static const uint TileAOuter = 64u;
 static const uint TileBOuter = 64u;
 static const uint TileInner = 64u;
+
 groupshared float mm_Asub[64][64];
 groupshared float mm_Bsub[64][64];