[hlsl-writer] Fix emission of struct aliases.

You can only typedef builtin types in HLSL. This Cl updates the struct
emission to emit named structs instead of typedef'd structs.

Bug: tint:7
Change-Id: I835b7f4d23bc225c730ef3f39c4572c043a58156
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/26921
Commit-Queue: dan sinclair <dsinclair@chromium.org>
Reviewed-by: David Neto <dneto@google.com>

src/writer/hlsl/generator_impl.cc

@@ -137,11 +137,19 @@ std::string GeneratorImpl::current_ep_var_name(VarType type) {
 
 bool GeneratorImpl::EmitAliasType(const ast::type::AliasType* alias) {
   make_indent();
-  out_ << "typedef ";
-  if (!EmitType(alias->type(), "")) {
-    return false;
+
+  if (alias->type()->IsStruct()) {
+    if (!EmitType(alias->type(), namer_.NameFor(alias->name()))) {
+      return false;
+    }
+    out_ << ";" << std::endl;
+  } else {
+    out_ << "typedef ";
+    if (!EmitType(alias->type(), "")) {
+      return false;
+    }
+    out_ << " " << namer_.NameFor(alias->name()) << ";" << std::endl;
   }
-  out_ << " " << namer_.NameFor(alias->name()) << ";" << std::endl;
 
   return true;
 }
@@ -1268,7 +1276,12 @@ bool GeneratorImpl::EmitType(ast::type::Type* type, const std::string& name) {
     // TODO(dsinclair): Block decoration?
     // if (str->decoration() != ast::StructDecoration::kNone) {
     // }
-    out_ << "struct {" << std::endl;
+    out_ << "struct";
+    // If a name was provided for the struct emit it.
+    if (!name.empty()) {
+      out_ << " " << name;
+    }
+    out_ << " {" << std::endl;
 
     increment_indent();
     for (const auto& mem : str->members()) {

src/writer/hlsl/generator_impl_alias_type_test.cc

@@ -74,10 +74,10 @@ TEST_F(HlslGeneratorImplTest, EmitAliasType_Struct) {
   ast::Module m;
   GeneratorImpl g(&m);
   ASSERT_TRUE(g.EmitAliasType(&alias)) << g.error();
-  EXPECT_EQ(g.result(), R"(typedef struct {
+  EXPECT_EQ(g.result(), R"(struct a {
   float a;
   int b;
-} a;
+};
 )");
 }
 

src/writer/hlsl/generator_impl_function_test.cc

@@ -402,9 +402,9 @@ TEST_F(HlslGeneratorImplTest, Emit_Function_EntryPoint_With_UniformStruct) {
 
   GeneratorImpl g(&mod);
   ASSERT_TRUE(g.Generate()) << g.error();
-  EXPECT_EQ(g.result(), R"(typedef struct {
+  EXPECT_EQ(g.result(), R"(struct Uniforms {
   vector<float, 4> coord;
-} Uniforms;
+};
 
 ConstantBuffer<Uniforms> uniforms : register(b0);