writer/msl: Simplify type constructor generation

The special-case for zero-valued constructors is unnecessary, as an
empty initializer list already correctly zero-initializes for all
types. This was causing an additional {} to be emitted for empty
structures, which the MSL compiler rejects.

Fixed: tint:821
Change-Id: Ib48c73eadef15b517e14b248229ecfbbfeb13f81
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/51822
Commit-Queue: James Price <jrprice@google.com>
Commit-Queue: Ben Clayton <bclayton@google.com>
Auto-Submit: James Price <jrprice@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>
Kokoro: Kokoro <noreply+kokoro@google.com>

src/writer/msl/generator_impl.cc

@@ -892,23 +892,15 @@ bool GeneratorImpl::EmitTypeConstructor(ast::TypeConstructorExpression* expr) {
     out_ << "(";
   }
 
-  // If the type constructor is empty then we need to construct with the zero
+  bool first = true;
-  // value for all components.
+  for (auto* e : expr->values()) {
-  if (expr->values().empty()) {
+    if (!first) {
-    if (!EmitZeroValue(type)) {
+      out_ << ", ";
-      return false;
     }
-  } else {
+    first = false;
-    bool first = true;
-    for (auto* e : expr->values()) {
-      if (!first) {
-        out_ << ", ";
-      }
-      first = false;
 
-      if (!EmitExpression(e)) {
+    if (!EmitExpression(e)) {
-        return false;
+      return false;
-      }
     }
   }
 

src/writer/msl/generator_impl_constructor_test.cc

@@ -112,7 +112,7 @@ TEST_F(MslGeneratorImplTest, EmitConstructor_Type_Vec_Empty) {
   GeneratorImpl& gen = Build();
 
   ASSERT_TRUE(gen.Generate()) << gen.error();
-  EXPECT_THAT(gen.result(), HasSubstr("float3(0.0f)"));
+  EXPECT_THAT(gen.result(), HasSubstr("float3()"));
 }
 
 TEST_F(MslGeneratorImplTest, EmitConstructor_Type_Mat) {
@@ -137,7 +137,7 @@ TEST_F(MslGeneratorImplTest, EmitConstructor_Type_Mat_Empty) {
   GeneratorImpl& gen = Build();
 
   ASSERT_TRUE(gen.Generate()) << gen.error();
-  EXPECT_THAT(gen.result(), HasSubstr("float4x4(0.0f)"));
+  EXPECT_THAT(gen.result(), HasSubstr("float4x4()"));
 }
 
 TEST_F(MslGeneratorImplTest, EmitConstructor_Type_Array) {
@@ -155,10 +155,10 @@ TEST_F(MslGeneratorImplTest, EmitConstructor_Type_Array) {
 
 TEST_F(MslGeneratorImplTest, EmitConstructor_Type_Struct) {
   auto* str = Structure("S", {
-                                Member("a", ty.i32()),
+                                 Member("a", ty.i32()),
-                                Member("b", ty.f32()),
+                                 Member("b", ty.f32()),
-                                Member("c", ty.vec3<i32>()),
+                                 Member("c", ty.vec3<i32>()),
-                            });
+                             });
 
   WrapInFunction(Construct(str, 1, 2.0f, vec3<i32>(3, 4, 5)));
 
@@ -168,6 +168,18 @@ TEST_F(MslGeneratorImplTest, EmitConstructor_Type_Struct) {
   EXPECT_THAT(gen.result(), HasSubstr("{1, 2.0f, int3(3, 4, 5)}"));
 }
 
+TEST_F(MslGeneratorImplTest, EmitConstructor_Type_Struct_Empty) {
+  auto* str = Structure("S", {});
+
+  WrapInFunction(Construct(str));
+
+  GeneratorImpl& gen = Build();
+
+  ASSERT_TRUE(gen.Generate()) << gen.error();
+  EXPECT_THAT(gen.result(), HasSubstr("{}"));
+  EXPECT_THAT(gen.result(), Not(HasSubstr("{{}}")));
+}
+
 }  // namespace
 }  // namespace msl
 }  // namespace writer

src/writer/msl/generator_impl_function_test.cc

@@ -214,7 +214,7 @@ struct tint_symbol_3 {
 };
 
 vertex tint_symbol vert_main() {
-  Interface const tint_symbol_1 = {0.5f, 0.25f, float4(0.0f)};
+  Interface const tint_symbol_1 = {0.5f, 0.25f, float4()};
   return {tint_symbol_1.col1, tint_symbol_1.col2, tint_symbol_1.pos};
 }
 

src/writer/msl/generator_impl_variable_decl_statement_test.cc

@@ -48,7 +48,7 @@ TEST_F(MslGeneratorImplTest, Emit_VariableDeclStatement_Const) {
   gen.increment_indent();
 
   ASSERT_TRUE(gen.EmitStatement(stmt)) << gen.error();
-  EXPECT_EQ(gen.result(), "  float const a = float(0.0f);\n");
+  EXPECT_EQ(gen.result(), "  float const a = float();\n");
 }
 
 TEST_F(MslGeneratorImplTest, Emit_VariableDeclStatement_Array) {
@@ -150,7 +150,7 @@ TEST_F(MslGeneratorImplTest, Emit_VariableDeclStatement_Initializer_ZeroVec) {
   GeneratorImpl& gen = Build();
 
   ASSERT_TRUE(gen.EmitStatement(stmt)) << gen.error();
-  EXPECT_EQ(gen.result(), R"(float3 a = float3(0.0f);
+  EXPECT_EQ(gen.result(), R"(float3 a = float3();
 )");
 }
 

test/samples/simple.wgsl.expected.msl

@@ -9,7 +9,7 @@ void bar() {
 }
 
 fragment tint_symbol_1 tint_symbol() {
-  float2 a = float2(0.0f);
+  float2 a = float2();
   bar();
   return {float4(0.400000006f, 0.400000006f, 0.800000012f, 1.0f)};
 }