[resolver] Add entry point IO validation

Checks the following things:
- Non-struct entry point parameters must have pipeline IO attributes
- Non-struct entry point return type must have a pipeline IO attribute
- Structs used as entry point parameters and return values much have
  pipeline IO attributes on every member
- Structs used as entry point parameters and return values cannot have
  runtime array or nested struct members
- Multiple pipeline IO attributes on a parameter, return type, or
  struct member is not allowed
- Any given builtin and location attribute can only appear once for
  the return type, and across all parameters

Removed tests for nested structs from the SPIR-V transform/backend.

Fixed a couple of other tests with missing pipeline IO attributes.

Fixed: tint:512
Change-Id: I4c48fe24099333c8c7fcd45934c09baa6830883c
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/46701
Auto-Submit: James Price <jrprice@google.com>
Reviewed-by: Antonio Maiorano <amaiorano@google.com>
Commit-Queue: Antonio Maiorano <amaiorano@google.com>
Kokoro: Kokoro <noreply+kokoro@google.com>

src/resolver/entry_point_validation_test.cc

@@ -0,0 +1,504 @@
+// Copyright 2021 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/ast/builtin_decoration.h"
+#include "src/ast/location_decoration.h"
+#include "src/ast/return_statement.h"
+#include "src/ast/stage_decoration.h"
+#include "src/ast/struct_block_decoration.h"
+#include "src/resolver/resolver.h"
+#include "src/resolver/resolver_test_helper.h"
+
+#include "gmock/gmock.h"
+
+namespace tint {
+namespace {
+
+class ResolverEntryPointValidationTest : public resolver::TestHelper,
+                                         public testing::Test {};
+
+TEST_F(ResolverEntryPointValidationTest, ReturnTypeAttribute_Location) {
+  // [[stage(vertex)]]
+  // fn main() -> [[location(0)]] f32 { return 1.0; }
+  Func(Source{{12, 34}}, "main", {}, ty.f32(), {Return(Expr(1.0f))},
+       {Stage(ast::PipelineStage::kVertex)}, {Location(0)});
+
+  EXPECT_TRUE(r()->Resolve()) << r()->error();
+}
+
+TEST_F(ResolverEntryPointValidationTest, ReturnTypeAttribute_Builtin) {
+  // [[stage(vertex)]]
+  // fn main() -> [[builtin(position)]] vec4<f32> { return vec4<f32>(); }
+  Func(Source{{12, 34}}, "main", {}, ty.vec4<f32>(),
+       {Return(Construct(ty.vec4<f32>()))},
+       {Stage(ast::PipelineStage::kVertex)},
+       {Builtin(ast::Builtin::kPosition)});
+
+  EXPECT_TRUE(r()->Resolve()) << r()->error();
+}
+
+TEST_F(ResolverEntryPointValidationTest, ReturnTypeAttribute_Missing) {
+  // [[stage(vertex)]]
+  // fn main() -> f32 {
+  //   return 1.0;
+  // }
+  Func(Source{{12, 34}}, "main", {}, ty.vec4<f32>(),
+       {Return(Construct(ty.vec4<f32>()))},
+       {Stage(ast::PipelineStage::kVertex)});
+
+  EXPECT_FALSE(r()->Resolve());
+  EXPECT_EQ(r()->error(),
+            "12:34 error: missing entry point IO attribute on return type");
+}
+
+TEST_F(ResolverEntryPointValidationTest, ReturnTypeAttribute_Multiple) {
+  // [[stage(vertex)]]
+  // fn main() -> [[location(0)]] [[builtin(position)]] vec4<f32> {
+  //   return vec4<f32>();
+  // }
+  Func(Source{{12, 34}}, "main", {}, ty.vec4<f32>(),
+       {Return(Construct(ty.vec4<f32>()))},
+       {Stage(ast::PipelineStage::kVertex)},
+       {Location(Source{{13, 43}}, 0),
+        Builtin(Source{{14, 52}}, ast::Builtin::kPosition)});
+
+  EXPECT_FALSE(r()->Resolve());
+  EXPECT_EQ(r()->error(), R"(14:52 error: multiple entry point IO attributes
+13:43 note: previously consumed location(0))");
+}
+
+TEST_F(ResolverEntryPointValidationTest, ReturnTypeAttribute_Struct) {
+  // struct Output {
+  // };
+  // [[stage(vertex)]]
+  // fn main() -> [[location(0)]] Output {
+  //   return Output();
+  // }
+  auto* output = Structure("Output", {});
+  Func(Source{{12, 34}}, "main", {}, output, {Return(Construct(output))},
+       {Stage(ast::PipelineStage::kVertex)}, {Location(Source{{13, 43}}, 0)});
+
+  EXPECT_FALSE(r()->Resolve());
+  EXPECT_EQ(
+      r()->error(),
+      "13:43 error: entry point IO attributes must not be used on structure "
+      "return types");
+}
+
+TEST_F(ResolverEntryPointValidationTest, ReturnType_Struct_Valid) {
+  // struct Output {
+  //   [[location(0)]] a : f32;
+  //   [[builtin(frag_depth)]] b : f32;
+  // };
+  // [[stage(fragment)]]
+  // fn main() -> Output {
+  //   return Output();
+  // }
+  auto* output = Structure(
+      "Output", {Member("a", ty.f32(), {Location(0)}),
+                 Member("b", ty.f32(), {Builtin(ast::Builtin::kFragDepth)})});
+  Func(Source{{12, 34}}, "main", {}, output, {Return(Construct(output))},
+       {Stage(ast::PipelineStage::kFragment)});
+
+  EXPECT_TRUE(r()->Resolve()) << r()->error();
+}
+
+TEST_F(ResolverEntryPointValidationTest,
+       ReturnType_Struct_MemberMultipleAttributes) {
+  // struct Output {
+  //   [[location(0)]] [[builtin(frag_depth)]] a : f32;
+  // };
+  // [[stage(fragment)]]
+  // fn main() -> Output {
+  //   return Output();
+  // }
+  auto* output = Structure(
+      "Output",
+      {Member("a", ty.f32(),
+              {Location(Source{{13, 43}}, 0),
+               Builtin(Source{{14, 52}}, ast::Builtin::kFragDepth)})});
+  Func(Source{{12, 34}}, "main", {}, output, {Return(Construct(output))},
+       {Stage(ast::PipelineStage::kFragment)});
+
+  EXPECT_FALSE(r()->Resolve());
+  EXPECT_EQ(r()->error(), R"(14:52 error: multiple entry point IO attributes
+13:43 note: previously consumed location(0)
+12:34 note: while analysing entry point main)");
+}
+
+TEST_F(ResolverEntryPointValidationTest,
+       ReturnType_Struct_MemberMissingAttribute) {
+  // struct Output {
+  //   [[location(0)]] a : f32;
+  //   b : f32;
+  // };
+  // [[stage(fragment)]]
+  // fn main() -> Output {
+  //   return Output();
+  // }
+  auto* output = Structure(
+      "Output", {Member(Source{{13, 43}}, "a", ty.f32(), {Location(0)}),
+                 Member(Source{{14, 52}}, "b", ty.f32(), {})});
+  Func(Source{{12, 34}}, "main", {}, output, {Return(Construct(output))},
+       {Stage(ast::PipelineStage::kFragment)});
+
+  EXPECT_FALSE(r()->Resolve());
+  EXPECT_EQ(r()->error(),
+            R"(14:52 error: missing entry point IO attribute
+12:34 note: while analysing entry point main)");
+}
+
+TEST_F(ResolverEntryPointValidationTest, ReturnType_Struct_NestedStruct) {
+  // struct Inner {
+  //   [[location(0)]] b : f32;
+  // };
+  // struct Output {
+  //   [[location(0)]] a : Inner;
+  // };
+  // [[stage(fragment)]]
+  // fn main() -> Output {
+  //   return Output();
+  // }
+  auto* inner = Structure(
+      "Inner", {Member(Source{{13, 43}}, "a", ty.f32(), {Location(0)})});
+  auto* output = Structure(
+      "Output", {Member(Source{{14, 52}}, "a", inner, {Location(0)})});
+  Func(Source{{12, 34}}, "main", {}, output, {Return(Construct(output))},
+       {Stage(ast::PipelineStage::kFragment)});
+
+  EXPECT_FALSE(r()->Resolve());
+  EXPECT_EQ(
+      r()->error(),
+      R"(14:52 error: entry point IO types cannot contain nested structures
+12:34 note: while analysing entry point main)");
+}
+
+TEST_F(ResolverEntryPointValidationTest, ReturnType_Struct_RuntimeArray) {
+  // [[block]]
+  // struct Output {
+  //   [[location(0)]] a : array<f32>;
+  // };
+  // [[stage(fragment)]]
+  // fn main() -> Output {
+  //   return Output();
+  // }
+  auto* output = Structure(
+      "Output",
+      {Member(Source{{13, 43}}, "a", ty.array<float>(), {Location(0)})},
+      {create<ast::StructBlockDecoration>()});
+  Func(Source{{12, 34}}, "main", {}, output, {Return(Construct(output))},
+       {Stage(ast::PipelineStage::kFragment)});
+
+  EXPECT_FALSE(r()->Resolve());
+  EXPECT_EQ(
+      r()->error(),
+      R"(13:43 error: entry point IO types cannot contain runtime sized arrays
+12:34 note: while analysing entry point main)");
+}
+
+TEST_F(ResolverEntryPointValidationTest, ReturnType_Struct_DuplicateBuiltins) {
+  // struct Output {
+  //   [[builtin(frag_depth)]] a : f32;
+  //   [[builtin(frag_depth)]] b : f32;
+  // };
+  // [[stage(fragment)]]
+  // fn main() -> Output {
+  //   return Output();
+  // }
+  auto* output = Structure(
+      "Output", {Member("a", ty.f32(), {Builtin(ast::Builtin::kFragDepth)}),
+                 Member("b", ty.f32(), {Builtin(ast::Builtin::kFragDepth)})});
+  Func(Source{{12, 34}}, "main", {}, output, {Return(Construct(output))},
+       {Stage(ast::PipelineStage::kFragment)});
+
+  EXPECT_FALSE(r()->Resolve());
+  EXPECT_EQ(
+      r()->error(),
+      R"(12:34 error: builtin(frag_depth) attribute appears multiple times as pipeline output
+12:34 note: while analysing entry point main)");
+}
+
+TEST_F(ResolverEntryPointValidationTest, ReturnType_Struct_DuplicateLocation) {
+  // struct Output {
+  //   [[location(1)]] a : f32;
+  //   [[location(1)]] b : f32;
+  // };
+  // [[stage(fragment)]]
+  // fn main() -> Output {
+  //   return Output();
+  // }
+  auto* output = Structure("Output", {Member("a", ty.f32(), {Location(1)}),
+                                      Member("b", ty.f32(), {Location(1)})});
+  Func(Source{{12, 34}}, "main", {}, output, {Return(Construct(output))},
+       {Stage(ast::PipelineStage::kFragment)});
+
+  EXPECT_FALSE(r()->Resolve());
+  EXPECT_EQ(
+      r()->error(),
+      R"(12:34 error: location(1) attribute appears multiple times as pipeline output
+12:34 note: while analysing entry point main)");
+}
+
+TEST_F(ResolverEntryPointValidationTest, ParameterAttribute_Location) {
+  // [[stage(fragment)]]
+  // fn main([[location(0)]] param : f32) {}
+  auto* param = Const("param", ty.f32(), nullptr, {Location(0)});
+  Func(Source{{12, 34}}, "main", {param}, ty.void_(), {},
+       {Stage(ast::PipelineStage::kFragment)});
+
+  EXPECT_TRUE(r()->Resolve()) << r()->error();
+}
+
+TEST_F(ResolverEntryPointValidationTest, ParameterAttribute_Builtin) {
+  // [[stage(fragment)]]
+  // fn main([[builtin(frag_depth)]] param : f32) {}
+  auto* param = Const("param", ty.vec4<f32>(), nullptr,
+                      {Builtin(ast::Builtin::kFragDepth)});
+  Func(Source{{12, 34}}, "main", {param}, ty.void_(), {},
+       {Stage(ast::PipelineStage::kFragment)});
+
+  EXPECT_TRUE(r()->Resolve()) << r()->error();
+}
+
+TEST_F(ResolverEntryPointValidationTest, ParameterAttribute_Missing) {
+  // [[stage(fragment)]]
+  // fn main(param : f32) {}
+  auto* param = Const(Source{{13, 43}}, "param", ty.vec4<f32>(), nullptr);
+  Func(Source{{12, 34}}, "main", {param}, ty.void_(), {},
+       {Stage(ast::PipelineStage::kFragment)});
+
+  EXPECT_FALSE(r()->Resolve());
+  EXPECT_EQ(r()->error(),
+            "13:43 error: missing entry point IO attribute on parameter");
+}
+
+TEST_F(ResolverEntryPointValidationTest, ParameterAttribute_Multiple) {
+  // [[stage(fragment)]]
+  // fn main([[location(0)]] [[builtin(vertex_index)]] param : u32) {}
+  auto* param = Const("param", ty.u32(), nullptr,
+                      {Location(Source{{13, 43}}, 0),
+                       Builtin(Source{{14, 52}}, ast::Builtin::kVertexIndex)});
+  Func(Source{{12, 34}}, "main", {param}, ty.void_(), {},
+       {Stage(ast::PipelineStage::kFragment)});
+
+  EXPECT_FALSE(r()->Resolve());
+  EXPECT_EQ(r()->error(), R"(14:52 error: multiple entry point IO attributes
+13:43 note: previously consumed location(0))");
+}
+
+TEST_F(ResolverEntryPointValidationTest, ParameterAttribute_Struct) {
+  // struct Input {
+  // };
+  // [[stage(fragment)]]
+  // fn main([[location(0)]] param : Input) {}
+  auto* input = Structure("Input", {});
+  auto* param = Const("param", input, nullptr, {Location(Source{{13, 43}}, 0)});
+  Func(Source{{12, 34}}, "main", {param}, ty.void_(), {},
+       {Stage(ast::PipelineStage::kFragment)});
+
+  EXPECT_FALSE(r()->Resolve());
+  EXPECT_EQ(
+      r()->error(),
+      "13:43 error: entry point IO attributes must not be used on structure "
+      "parameters");
+}
+
+TEST_F(ResolverEntryPointValidationTest, Parameter_Struct_Valid) {
+  // struct Input {
+  //   [[location(0)]] a : f32;
+  //   [[builtin(sample_index)]] b : u32;
+  // };
+  // [[stage(fragment)]]
+  // fn main(param : Input) {}
+  auto* input = Structure(
+      "Input", {Member("a", ty.f32(), {Location(0)}),
+                Member("b", ty.u32(), {Builtin(ast::Builtin::kSampleIndex)})});
+  auto* param = Const("param", input);
+  Func(Source{{12, 34}}, "main", {param}, ty.void_(), {},
+       {Stage(ast::PipelineStage::kFragment)});
+
+  EXPECT_TRUE(r()->Resolve()) << r()->error();
+}
+
+TEST_F(ResolverEntryPointValidationTest,
+       Parameter_Struct_MemberMultipleAttributes) {
+  // struct Input {
+  //   [[location(0)]] [[builtin(sample_index)]] a : u32;
+  // };
+  // [[stage(fragment)]]
+  // fn main(param : Input) {}
+  auto* input = Structure(
+      "Input",
+      {Member("a", ty.f32(),
+              {Location(Source{{13, 43}}, 0),
+               Builtin(Source{{14, 52}}, ast::Builtin::kSampleIndex)})});
+  auto* param = Const("param", input);
+  Func(Source{{12, 34}}, "main", {param}, ty.void_(), {},
+       {Stage(ast::PipelineStage::kFragment)});
+
+  EXPECT_FALSE(r()->Resolve());
+  EXPECT_EQ(r()->error(), R"(14:52 error: multiple entry point IO attributes
+13:43 note: previously consumed location(0)
+12:34 note: while analysing entry point main)");
+}
+
+TEST_F(ResolverEntryPointValidationTest,
+       Parameter_Struct_MemberMissingAttribute) {
+  // struct Input {
+  //   [[location(0)]] a : f32;
+  //   b : f32;
+  // };
+  // [[stage(fragment)]]
+  // fn main(param : Input) {}
+  auto* input = Structure(
+      "Input", {Member(Source{{13, 43}}, "a", ty.f32(), {Location(0)}),
+                Member(Source{{14, 52}}, "b", ty.f32(), {})});
+  auto* param = Const("param", input);
+  Func(Source{{12, 34}}, "main", {param}, ty.void_(), {},
+       {Stage(ast::PipelineStage::kFragment)});
+
+  EXPECT_FALSE(r()->Resolve());
+  EXPECT_EQ(r()->error(), R"(14:52 error: missing entry point IO attribute
+12:34 note: while analysing entry point main)");
+}
+
+TEST_F(ResolverEntryPointValidationTest, Parameter_Struct_NestedStruct) {
+  // struct Inner {
+  //   [[location(0)]] b : f32;
+  // };
+  // struct Input {
+  //   [[location(0)]] a : Inner;
+  // };
+  // [[stage(fragment)]]
+  // fn main(param : Input) {}
+  auto* inner = Structure(
+      "Inner", {Member(Source{{13, 43}}, "a", ty.f32(), {Location(0)})});
+  auto* input =
+      Structure("Input", {Member(Source{{14, 52}}, "a", inner, {Location(0)})});
+  auto* param = Const("param", input);
+  Func(Source{{12, 34}}, "main", {param}, ty.void_(), {},
+       {Stage(ast::PipelineStage::kFragment)});
+
+  EXPECT_FALSE(r()->Resolve());
+  EXPECT_EQ(
+      r()->error(),
+      R"(14:52 error: entry point IO types cannot contain nested structures
+12:34 note: while analysing entry point main)");
+}
+
+TEST_F(ResolverEntryPointValidationTest, Parameter_Struct_RuntimeArray) {
+  // [[block]]
+  // struct Input {
+  //   [[location(0)]] a : array<f32>;
+  // };
+  // [[stage(fragment)]]
+  // fn main(param : Input) {}
+  auto* input = Structure(
+      "Input",
+      {Member(Source{{13, 43}}, "a", ty.array<float>(), {Location(0)})},
+      {create<ast::StructBlockDecoration>()});
+  auto* param = Const("param", input);
+  Func(Source{{12, 34}}, "main", {param}, ty.void_(), {},
+       {Stage(ast::PipelineStage::kFragment)});
+
+  EXPECT_FALSE(r()->Resolve());
+  EXPECT_EQ(
+      r()->error(),
+      R"(13:43 error: entry point IO types cannot contain runtime sized arrays
+12:34 note: while analysing entry point main)");
+}
+
+TEST_F(ResolverEntryPointValidationTest, Parameter_DuplicateBuiltins) {
+  // [[stage(fragment)]]
+  // fn main([[builtin(sample_index)]] param_a : u32,
+  //         [[builtin(sample_index)]] param_b : u32) {}
+  auto* param_a = Const("param_a", ty.u32(), nullptr,
+                        {Builtin(ast::Builtin::kSampleIndex)});
+  auto* param_b = Const("param_b", ty.u32(), nullptr,
+                        {Builtin(ast::Builtin::kSampleIndex)});
+  Func(Source{{12, 34}}, "main", {param_a, param_b}, ty.void_(), {},
+       {Stage(ast::PipelineStage::kFragment)});
+
+  EXPECT_FALSE(r()->Resolve());
+  EXPECT_EQ(
+      r()->error(),
+      "12:34 error: builtin(sample_index) attribute appears multiple times as "
+      "pipeline input");
+}
+
+TEST_F(ResolverEntryPointValidationTest, Parameter_Struct_DuplicateBuiltins) {
+  // struct InputA {
+  //   [[builtin(sample_index)]] a : u32;
+  // };
+  // struct InputB {
+  //   [[builtin(sample_index)]] a : u32;
+  // };
+  // [[stage(fragment)]]
+  // fn main(param_a : InputA, param_b : InputB) {}
+  auto* input_a = Structure(
+      "InputA", {Member("a", ty.u32(), {Builtin(ast::Builtin::kSampleIndex)})});
+  auto* input_b = Structure(
+      "InputB", {Member("a", ty.u32(), {Builtin(ast::Builtin::kSampleIndex)})});
+  auto* param_a = Const("param_a", input_a);
+  auto* param_b = Const("param_b", input_b);
+  Func(Source{{12, 34}}, "main", {param_a, param_b}, ty.void_(), {},
+       {Stage(ast::PipelineStage::kFragment)});
+
+  EXPECT_FALSE(r()->Resolve());
+  EXPECT_EQ(
+      r()->error(),
+      R"(12:34 error: builtin(sample_index) attribute appears multiple times as pipeline input
+12:34 note: while analysing entry point main)");
+}
+
+TEST_F(ResolverEntryPointValidationTest, Parameter_DuplicateLocation) {
+  // [[stage(fragment)]]
+  // fn main([[location(1)]] param_a : f32,
+  //         [[location(1)]] param_b : f32) {}
+  auto* param_a = Const("param_a", ty.u32(), nullptr, {Location(1)});
+  auto* param_b = Const("param_b", ty.u32(), nullptr, {Location(1)});
+  Func(Source{{12, 34}}, "main", {param_a, param_b}, ty.void_(), {},
+       {Stage(ast::PipelineStage::kFragment)});
+
+  EXPECT_FALSE(r()->Resolve());
+  EXPECT_EQ(r()->error(),
+            "12:34 error: location(1) attribute appears multiple times as "
+            "pipeline input");
+}
+
+TEST_F(ResolverEntryPointValidationTest, Parameter_Struct_DuplicateLocation) {
+  // struct InputA {
+  //   [[location(1)]] a : f32;
+  // };
+  // struct InputB {
+  //   [[location(1)]] a : f32;
+  // };
+  // [[stage(fragment)]]
+  // fn main(param_a : InputA, param_b : InputB) {}
+  auto* input_a = Structure("InputA", {Member("a", ty.f32(), {Location(1)})});
+  auto* input_b = Structure("InputB", {Member("a", ty.f32(), {Location(1)})});
+  auto* param_a = Const("param_a", input_a);
+  auto* param_b = Const("param_b", input_b);
+  Func(Source{{12, 34}}, "main", {param_a, param_b}, ty.void_(), {},
+       {Stage(ast::PipelineStage::kFragment)});
+
+  EXPECT_FALSE(r()->Resolve());
+  EXPECT_EQ(
+      r()->error(),
+      R"(12:34 error: location(1) attribute appears multiple times as pipeline input
+12:34 note: while analysing entry point main)");
+}
+
+}  // namespace
+}  // namespace tint

src/resolver/resolver.cc

@@ -268,8 +268,7 @@ bool Resolver::ValidateFunction(const ast::Function* func) {
     }
 
     for (auto* deco : func->return_type_decorations()) {
-      if (!(deco->Is<ast::BuiltinDecoration>() ||
-            deco->Is<ast::LocationDecoration>())) {
+      if (!deco->IsAnyOf<ast::BuiltinDecoration, ast::LocationDecoration>()) {
         diagnostics_.add_error(
             "decoration is not valid for function return types",
             deco->source());
@@ -278,6 +277,186 @@ bool Resolver::ValidateFunction(const ast::Function* func) {
     }
   }
 
+  if (func->IsEntryPoint()) {
+    if (!ValidateEntryPoint(func)) {
+      return false;
+    }
+  }
+
+  return true;
+}
+
+bool Resolver::ValidateEntryPoint(const ast::Function* func) {
+  // Use a lambda to validate the entry point decorations for a type.
+  // Persistent state is used to track which builtins and locations have already
+  // been seen, in order to catch conflicts.
+  // TODO(jrprice): This state could be stored in FunctionInfo instead, and then
+  // passed to semantic::Function since it would be useful there too.
+  std::unordered_set<ast::Builtin> builtins;
+  std::unordered_set<uint32_t> locations;
+  enum class ParamOrRetType {
+    kParameter,
+    kReturnType,
+  };
+  // Helper to stringify a pipeline IO decoration.
+  auto deco_to_str = [](const ast::Decoration* deco) {
+    std::stringstream str;
+    if (auto* builtin = deco->As<ast::BuiltinDecoration>()) {
+      str << "builtin(" << builtin->value() << ")";
+    } else if (auto* location = deco->As<ast::LocationDecoration>()) {
+      str << "location(" << location->value() << ")";
+    }
+    return str.str();
+  };
+  // Inner lambda that is applied to a type and all of its members.
+  auto validate_entry_point_decorations_inner =
+      [&](const ast::DecorationList& decos, type::Type* ty, Source source,
+          ParamOrRetType param_or_ret, bool is_struct_member) {
+        // Scan decorations for pipeline IO attributes.
+        // Check for overlap with attributes that have been seen previously.
+        ast::Decoration* pipeline_io_attribute = nullptr;
+        for (auto* deco : decos) {
+          if (auto* builtin = deco->As<ast::BuiltinDecoration>()) {
+            if (pipeline_io_attribute) {
+              diagnostics_.add_error("multiple entry point IO attributes",
+                                     deco->source());
+              diagnostics_.add_note(
+                  "previously consumed " + deco_to_str(pipeline_io_attribute),
+                  pipeline_io_attribute->source());
+              return false;
+            }
+            pipeline_io_attribute = deco;
+
+            if (builtins.count(builtin->value())) {
+              diagnostics_.add_error(
+                  deco_to_str(builtin) +
+                      " attribute appears multiple times as pipeline " +
+                      (param_or_ret == ParamOrRetType::kParameter ? "input"
+                                                                  : "output"),
+                  func->source());
+              return false;
+            }
+            builtins.emplace(builtin->value());
+
+          } else if (auto* location = deco->As<ast::LocationDecoration>()) {
+            if (pipeline_io_attribute) {
+              diagnostics_.add_error("multiple entry point IO attributes",
+                                     deco->source());
+              diagnostics_.add_note(
+                  "previously consumed " + deco_to_str(pipeline_io_attribute),
+                  pipeline_io_attribute->source());
+              return false;
+            }
+            pipeline_io_attribute = deco;
+
+            if (locations.count(location->value())) {
+              diagnostics_.add_error(
+                  deco_to_str(location) +
+                      " attribute appears multiple times as pipeline " +
+                      (param_or_ret == ParamOrRetType::kParameter ? "input"
+                                                                  : "output"),
+                  func->source());
+              return false;
+            }
+            locations.emplace(location->value());
+          }
+        }
+
+        // Check that we saw a pipeline IO attribute iff we need one.
+        if (ty->UnwrapAliasIfNeeded()->Is<type::Struct>()) {
+          if (pipeline_io_attribute) {
+            diagnostics_.add_error(
+                "entry point IO attributes must not be used on structure " +
+                    std::string(param_or_ret == ParamOrRetType::kParameter
+                                    ? "parameters"
+                                    : "return types"),
+                pipeline_io_attribute->source());
+            return false;
+          }
+        } else {
+          if (!pipeline_io_attribute) {
+            std::string err = "missing entry point IO attribute";
+            if (!is_struct_member) {
+              err += (param_or_ret == ParamOrRetType::kParameter
+                          ? " on parameter"
+                          : " on return type");
+            }
+            diagnostics_.add_error(err, source);
+            return false;
+          }
+        }
+
+        return true;
+      };
+
+  // Outer lambda for validating the entry point decorations for a type.
+  auto validate_entry_point_decorations = [&](const ast::DecorationList& decos,
+                                              type::Type* ty, Source source,
+                                              ParamOrRetType param_or_ret) {
+    // Validate the decorations for the type.
+    if (!validate_entry_point_decorations_inner(decos, ty, source, param_or_ret,
+                                                false)) {
+      return false;
+    }
+
+    if (auto* struct_ty = ty->UnwrapAliasIfNeeded()->As<type::Struct>()) {
+      // Validate the decorations for each struct members, and also check for
+      // invalid member types.
+      for (auto* member : struct_ty->impl()->members()) {
+        auto* member_ty = member->type()->UnwrapAliasIfNeeded();
+        if (member_ty->Is<type::Struct>()) {
+          diagnostics_.add_error(
+              "entry point IO types cannot contain nested structures",
+              member->source());
+          diagnostics_.add_note("while analysing entry point " +
+                                    builder_->Symbols().NameFor(func->symbol()),
+                                func->source());
+          return false;
+        } else if (auto* arr = member_ty->As<type::Array>()) {
+          if (arr->IsRuntimeArray()) {
+            diagnostics_.add_error(
+                "entry point IO types cannot contain runtime sized arrays",
+                member->source());
+            diagnostics_.add_note(
+                "while analysing entry point " +
+                    builder_->Symbols().NameFor(func->symbol()),
+                func->source());
+            return false;
+          }
+        }
+
+        if (!validate_entry_point_decorations_inner(member->decorations(),
+                                                    member_ty, member->source(),
+                                                    param_or_ret, true)) {
+          diagnostics_.add_note("while analysing entry point " +
+                                    builder_->Symbols().NameFor(func->symbol()),
+                                func->source());
+          return false;
+        }
+      }
+    }
+
+    return true;
+  };
+
+  for (auto* param : func->params()) {
+    if (!validate_entry_point_decorations(
+            param->decorations(), param->declared_type(), param->source(),
+            ParamOrRetType::kParameter)) {
+      return false;
+    }
+  }
+
+  if (!func->return_type()->Is<type::Void>()) {
+    builtins.clear();
+    locations.clear();
+    if (!validate_entry_point_decorations(func->return_type_decorations(),
+                                          func->return_type(), func->source(),
+                                          ParamOrRetType::kReturnType)) {
+      return false;
+    }
+  }
+
   return true;
 }
 

src/resolver/resolver.h

@@ -234,6 +234,7 @@ class Resolver {
   bool ValidateVariable(const ast::Variable* param);
   bool ValidateParameter(const ast::Variable* param);
   bool ValidateFunction(const ast::Function* func);
+  bool ValidateEntryPoint(const ast::Function* func);
   bool ValidateStructure(const type::Struct* st);
   bool ValidateReturn(const ast::ReturnStatement* ret);
   bool ValidateSwitch(const ast::SwitchStatement* s);