[validation] v-15001: front_facing builtin must be boolean

To declare a front_facing builtin variable
- declare as a parameter of the entry point function or it can be
- declared as members of structures that are entry point function parameters
The type of the function-parameter/structure-member must be boolean.

Bug: tint:357
Change-Id: I09c380ae5784d29e776e483d966a0f7d8cd2286c
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/53821
Reviewed-by: Sarah Mashayekhi <sarahmashay@google.com>
Reviewed-by: Antonio Maiorano <amaiorano@google.com>
Kokoro: Kokoro <noreply+kokoro@google.com>
Commit-Queue: Sarah Mashayekhi <sarahmashay@google.com>

src/resolver/builtins_validation_test.cc

@@ -20,6 +20,73 @@ namespace {
 class ResolverBuiltinsValidationTest : public resolver::TestHelper,
                                        public testing::Test {};
 
+TEST_F(ResolverBuiltinsValidationTest, FrontFacingParamIsBool_Pass) {
+  // [[stage(fragment)]]
+  // fn fs_main(
+  //   [[builtin(front_facing)]] is_front: bool
+  // ) -> [[location(0)]] f32 { return 1.0; }
+  auto* is_front =
+      Param("is_front", ty.bool_(),
+            ast::DecorationList{Builtin(ast::Builtin::kFrontFacing)});
+  Func("fs_main", ast::VariableList{is_front}, ty.f32(), {Return(1.0f)},
+       ast::DecorationList{Stage(ast::PipelineStage::kFragment)},
+       {Location(0)});
+  EXPECT_TRUE(r()->Resolve()) << r()->error();
+}
+
+TEST_F(ResolverBuiltinsValidationTest, FrontFacingMemberIsBool_Pass) {
+  // struct MyInputs {
+  //   [[builtin(front_facing)]] pos: bool;
+  // };
+  // [[stage(fragment)]]
+  // fn fragShader(is_front: MyInputs) -> [[location(0)]] f32 { return 1.0; }
+
+  auto* s = Structure(
+      "MyInputs",
+      {Member("pos", ty.bool_(),
+              ast::DecorationList{Builtin(ast::Builtin::kFrontFacing)})});
+  Func("fragShader", {Param("is_front", ty.Of(s))}, ty.f32(), {Return(1.0f)},
+       {Stage(ast::PipelineStage::kFragment)}, {Location(0)});
+  EXPECT_TRUE(r()->Resolve()) << r()->error();
+}
+
+TEST_F(ResolverBuiltinsValidationTest, FrontFacingParamIsNotBool_Fail) {
+  // [[stage(fragment)]]
+  // fn fs_main(
+  //   [[builtin(front_facing)]] is_front: i32;
+  // ) -> [[location(0)]] f32 { return 1.0; }
+
+  auto* is_front = Param("is_front", ty.i32(),
+                         ast::DecorationList{Builtin(
+                             Source{{12, 34}}, ast::Builtin::kFrontFacing)});
+  Func("fs_main", ast::VariableList{is_front}, ty.f32(), {Return(1.0f)},
+       ast::DecorationList{Stage(ast::PipelineStage::kFragment)},
+       {Location(0)});
+
+  EXPECT_FALSE(r()->Resolve());
+  EXPECT_EQ(r()->error(),
+            "12:34 error v-15001: front_facing builtin must be boolean");
+}
+
+TEST_F(ResolverBuiltinsValidationTest, FrontFacingMemberIsNotBool_Fail) {
+  // struct MyInputs {
+  //   [[builtin(front_facing)]] pos: f32;
+  // };
+  // [[stage(fragment)]]
+  // fn fragShader(is_front: MyInputs) -> [[location(0)]] f32 { return 1.0; }
+
+  auto* s = Structure(
+      "MyInputs", {Member("pos", ty.f32(),
+                          ast::DecorationList{Builtin(
+                              Source{{12, 34}}, ast::Builtin::kFrontFacing)})});
+  Func("fragShader", {Param("is_front", ty.Of(s))}, ty.f32(), {Return(1.0f)},
+       {Stage(ast::PipelineStage::kFragment)}, {Location(0)});
+
+  EXPECT_FALSE(r()->Resolve());
+  EXPECT_EQ(r()->error(),
+            "12:34 error v-15001: front_facing builtin must be boolean");
+}
+
 TEST_F(ResolverBuiltinsValidationTest, Length_Float_Scalar) {
   auto* builtin = Call("length", 1.0f);
   WrapInFunction(builtin);

src/resolver/resolver.cc

@@ -808,6 +808,21 @@ bool Resolver::ValidateVariable(const VariableInfo* info) {
 }
 
 bool Resolver::ValidateParameter(const VariableInfo* info) {
+  auto* var = info->declaration;
+  for (auto* deco : var->decorations()) {
+    if (auto* builtin = deco->As<ast::BuiltinDecoration>()) {
+      if (builtin->value() == ast::Builtin::kFrontFacing) {
+        auto* storage_type = info->type->UnwrapRef();
+        if (!(storage_type->Is<sem::Bool>())) {
+          diagnostics_.add_error("v-15001",
+                                 "front_facing builtin must be boolean",
+                                 deco->source());
+          return false;
+        }
+      }
+    }
+  }
+
   return ValidateVariable(info);
 }
 
@@ -2876,6 +2891,16 @@ bool Resolver::ValidateStructure(const sem::Struct* str) {
                                deco->source());
         return false;
       }
+      if (auto* builtin = deco->As<ast::BuiltinDecoration>()) {
+        if (builtin->value() == ast::Builtin::kFrontFacing) {
+          if (!(member->Type()->Is<sem::Bool>())) {
+            diagnostics_.add_error("v-15001",
+                                   "front_facing builtin must be boolean",
+                                   deco->source());
+            return false;
+          }
+        }
+      }
     }
   }