wgsl: Implement invariant attribute

Make sure the other backends ICE on unrecognized attributes.

Add E2E tests, currently skipped for the other backends.

Bug: tint:772
Change-Id: I4e68d111ff79b19ebb6c574058a91debcb746011
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/57642
Commit-Queue: Ben Clayton <bclayton@google.com>
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>

src/reader/wgsl/parser_impl.cc

@@ -24,6 +24,7 @@
 #include "src/ast/external_texture.h"
 #include "src/ast/fallthrough_statement.h"
 #include "src/ast/if_statement.h"
+#include "src/ast/invariant_decoration.h"
 #include "src/ast/loop_statement.h"
 #include "src/ast/override_decoration.h"
 #include "src/ast/return_statement.h"
@@ -111,6 +112,7 @@ const char kBlockDecoration[] = "block";
 const char kBuiltinDecoration[] = "builtin";
 const char kGroupDecoration[] = "group";
 const char kInterpolateDecoration[] = "interpolate";
+const char kInvariantDecoration[] = "invariant";
 const char kLocationDecoration[] = "location";
 const char kOverrideDecoration[] = "override";
 const char kSizeDecoration[] = "size";
@@ -3002,6 +3004,10 @@ Maybe<ast::Decoration*> ParserImpl::decoration() {
     });
   }
 
+  if (s == kInvariantDecoration) {
+    return create<ast::InvariantDecoration>(t.source());
+  }
+
   if (s == kBuiltinDecoration) {
     return expect_paren_block("builtin decoration", [&]() -> Result {
       auto builtin = expect_builtin();

src/reader/wgsl/parser_impl_function_header_test.cc

@@ -61,6 +61,20 @@ TEST_F(ParserImplTest, FunctionHeader_DecoratedReturnType) {
   EXPECT_EQ(loc->value(), 1u);
 }
 
+TEST_F(ParserImplTest, FunctionHeader_InvariantReturnType) {
+  auto p = parser("fn main() -> [[invariant]] f32");
+  auto f = p->function_header();
+  ASSERT_FALSE(p->has_error()) << p->error();
+  EXPECT_TRUE(f.matched);
+  EXPECT_FALSE(f.errored);
+
+  EXPECT_EQ(f->name, "main");
+  EXPECT_EQ(f->params.size(), 0u);
+  EXPECT_TRUE(f->return_type->Is<ast::F32>());
+  ASSERT_EQ(f->return_type_decorations.size(), 1u);
+  EXPECT_TRUE(f->return_type_decorations[0]->Is<ast::InvariantDecoration>());
+}
+
 TEST_F(ParserImplTest, FunctionHeader_DecoratedReturnType_WithArrayStride) {
   auto p = parser("fn main() -> [[location(1), stride(16)]] array<f32, 4>");
   auto f = p->function_header();

src/writer/hlsl/generator_impl.cc

@@ -3092,6 +3092,11 @@ bool GeneratorImpl::EmitStructType(const sem::Struct* str) {
             return false;
           }
           pre += mod;
+
+        } else if (!deco->IsAnyOf<ast::StructMemberAlignDecoration,
+                                  ast::StructMemberSizeDecoration>()) {
+          TINT_ICE(Writer, diagnostics_)
+              << "unhandled struct member attribute: " << deco->name();
         }
       }
 

src/writer/msl/generator_impl.cc

@@ -2134,6 +2134,11 @@ bool GeneratorImpl::EmitStructType(const sem::Struct* str) {
           return false;
         }
         out << " [[" << attr << "]]";
+      } else if (!deco->IsAnyOf<ast::StructMemberOffsetDecoration,
+                                ast::StructMemberAlignDecoration,
+                                ast::StructMemberSizeDecoration>()) {
+        TINT_ICE(Writer, diagnostics_)
+            << "unhandled struct member attribute: " << deco->name();
       }
     }
 

src/writer/wgsl/generator_impl.cc

@@ -30,6 +30,7 @@
 #include "src/ast/i32.h"
 #include "src/ast/internal_decoration.h"
 #include "src/ast/interpolate_decoration.h"
+#include "src/ast/invariant_decoration.h"
 #include "src/ast/matrix.h"
 #include "src/ast/module.h"
 #include "src/ast/multisampled_texture.h"
@@ -676,6 +677,8 @@ bool GeneratorImpl::EmitDecorations(std::ostream& out,
         out << ", " << interpolate->sampling();
       }
       out << ")";
+    } else if (deco->Is<ast::InvariantDecoration>()) {
+      out << "invariant";
     } else if (auto* override_deco = deco->As<ast::OverrideDecoration>()) {
       out << "override";
       if (override_deco->HasValue()) {