tint/ast: Add 'const' AST node

Nothing currently generates or consumes these (yet).

Bug: tint:1580
Change-Id: I892956d33fcd587be85659781108a236b2839b3c
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/94323
Commit-Queue: Ben Clayton <bclayton@chromium.org>
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: Dan Sinclair <dsinclair@chromium.org>

src/tint/BUILD.gn

@@ -213,6 +213,8 @@ libtint_source_set("libtint_core_all_src") {
     "ast/case_statement.h",
     "ast/compound_assignment_statement.cc",
     "ast/compound_assignment_statement.h",
+    "ast/const.cc",
+    "ast/const.h",
     "ast/continue_statement.cc",
     "ast/continue_statement.h",
     "ast/depth_multisampled_texture.cc",

src/tint/CMakeLists.txt

@@ -99,6 +99,8 @@ set(TINT_LIB_SRCS
   ast/case_statement.h
   ast/compound_assignment_statement.cc
   ast/compound_assignment_statement.h
+  ast/const.cc
+  ast/const.h
   ast/continue_statement.cc
   ast/continue_statement.h
   ast/depth_multisampled_texture.cc

src/tint/ast/const.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/const.h"
+
+#include "src/tint/program_builder.h"
+
+TINT_INSTANTIATE_TYPEINFO(tint::ast::Const);
+
+namespace tint::ast {
+
+Const::Const(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);
+}
+
+Const::Const(Const&&) = default;
+
+Const::~Const() = default;
+
+const Const* Const::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<Const>(src, sym, ty, ctor, attrs);
+}
+
+}  // namespace tint::ast

src/tint/ast/const.h

@@ -0,0 +1,64 @@
+// 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_CONST_H_
+#define SRC_TINT_AST_CONST_H_
+
+#include "src/tint/ast/variable.h"
+
+namespace tint::ast {
+
+/// A "const" declaration is a name for a module-scoped or function-scoped creation-time value.
+/// const must have a constructor expression.
+///
+/// Examples:
+///
+/// ```
+///   const n  = 123;                           // Abstract-integer typed constant
+///   const pi = 3.14159265359;                 // Abstract-float typed constant
+///   const max_f32 : f32 = 0x1.fffffep+127;    // f32 typed constant
+/// ```
+/// @see https://www.w3.org/TR/WGSL/#creation-time-consts
+class Const final : public Castable<Const, Variable> {
+  public:
+    /// Create a 'const' 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 constructor the constructor expression. Must not be nullptr.
+    /// @param attributes the variable attributes
+    Const(ProgramID program_id,
+          const Source& source,
+          const Symbol& sym,
+          const ast::Type* type,
+          const Expression* constructor,
+          AttributeList attributes);
+
+    /// Move constructor
+    Const(Const&&);
+
+    /// Destructor
+    ~Const() override;
+
+    /// Clones this node and all transitive child nodes using the `CloneContext`
+    /// `ctx`.
+    /// @param ctx the clone context
+    /// @return the newly cloned node
+    const Const* Clone(CloneContext* ctx) const override;
+};
+
+}  // namespace tint::ast
+
+#endif  // SRC_TINT_AST_CONST_H_