[wgsl-writer] Function var decls don't mention storage class

From WGSL decision in https://github.com/gpuweb/gpuweb/issues/654

Change-Id: I570475cf0d069043d70794d7b92626798963bfdc
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/21363
Reviewed-by: dan sinclair <dsinclair@google.com>

src/writer/wgsl/generator_impl.cc

@@ -466,7 +466,8 @@ bool GeneratorImpl::EmitVariable(ast::Variable* var) {
     out_ << "const";
   } else {
     out_ << "var";
-    if (var->storage_class() != ast::StorageClass::kNone) {
+    if (var->storage_class() != ast::StorageClass::kNone &&
+        var->storage_class() != ast::StorageClass::kFunction) {
       out_ << "<" << var->storage_class() << ">";
     }
   }

src/writer/wgsl/generator_impl_variable_decl_statement_test.cc

@@ -42,6 +42,37 @@ TEST_F(GeneratorImplTest, Emit_VariableDeclStatement) {
   EXPECT_EQ(g.result(), "  var a : f32;\n");
 }
 
+TEST_F(GeneratorImplTest, Emit_VariableDeclStatement_Function) {
+  // Variable declarations with Function storage class don't mention their
+  // storage class.  Rely on defaulting.
+  // https://github.com/gpuweb/gpuweb/issues/654
+  ast::type::F32Type f32;
+  auto var =
+      std::make_unique<ast::Variable>("a", ast::StorageClass::kFunction, &f32);
+
+  ast::VariableDeclStatement stmt(std::move(var));
+
+  GeneratorImpl g;
+  g.increment_indent();
+
+  ASSERT_TRUE(g.EmitStatement(&stmt)) << g.error();
+  EXPECT_EQ(g.result(), "  var a : f32;\n");
+}
+
+TEST_F(GeneratorImplTest, Emit_VariableDeclStatement_Private) {
+  ast::type::F32Type f32;
+  auto var =
+      std::make_unique<ast::Variable>("a", ast::StorageClass::kPrivate, &f32);
+
+  ast::VariableDeclStatement stmt(std::move(var));
+
+  GeneratorImpl g;
+  g.increment_indent();
+
+  ASSERT_TRUE(g.EmitStatement(&stmt)) << g.error();
+  EXPECT_EQ(g.result(), "  var<private> a : f32;\n");
+}
+
 }  // namespace
 }  // namespace wgsl
 }  // namespace writer