Add texture_external parsing and intrinsic overloads

Adds texture_external to ParserImpl. Adds texture_external overloads to
TextureSample, TextureLoad, and TextureDimensions to the intrisic table.
Adds corresponding tests.

Bug: dawn:728
Change-Id: I5e5557a10327f8c3d3044319decd748f812ecf3e
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/48722
Reviewed-by: Ben Clayton <bclayton@google.com>
Kokoro: Kokoro <noreply+kokoro@google.com>
Commit-Queue: Ben Clayton <bclayton@google.com>

src/reader/wgsl/lexer.cc

@@ -650,6 +650,9 @@ Token Lexer::check_keyword(const Source& source, const std::string& str) {
     return {Token::Type::kTextureDepthCubeArray, source,
             "texture_depth_cube_array"};
   }
+  if (str == "texture_external") {
+    return {Token::Type::kTextureExternal, source, "texture_external"};
+  }
   if (str == "texture_multisampled_2d") {
     return {Token::Type::kTextureMultisampled2d, source,
             "texture_multisampled_2d"};

src/reader/wgsl/parser_impl.cc

@@ -26,6 +26,7 @@
 #include "src/reader/wgsl/lexer.h"
 #include "src/sem/access_control_type.h"
 #include "src/sem/depth_texture_type.h"
+#include "src/sem/external_texture_type.h"
 #include "src/sem/multisampled_texture_type.h"
 #include "src/sem/sampled_texture_type.h"
 
@@ -516,6 +517,10 @@ Maybe<sem::Type*> ParserImpl::texture_sampler_types() {
   if (type.matched)
     return type.value;
 
+  type = external_texture_type();
+  if (type.matched)
+    return type.value;
+
   auto dim = sampled_texture_type();
   if (dim.matched) {
     const char* use = "sampled texture type";
@@ -600,6 +605,16 @@ Maybe<ast::TextureDimension> ParserImpl::sampled_texture_type() {
   return Failure::kNoMatch;
 }
 
+// external_texture_type
+//  : TEXTURE_EXTERNAL
+Maybe<sem::Type*> ParserImpl::external_texture_type() {
+  if (match(Token::Type::kTextureExternal)) {
+    return builder_.create<sem::ExternalTexture>();
+  }
+
+  return Failure::kNoMatch;
+}
+
 // multisampled_texture_type
 //  : TEXTURE_MULTISAMPLED_2D
 Maybe<ast::TextureDimension> ParserImpl::multisampled_texture_type() {

src/reader/wgsl/parser_impl.h

@@ -414,6 +414,9 @@ class ParserImpl {
   /// Parses a `depth_texture_type` grammar element
   /// @returns the parsed Type or nullptr if none matched.
   Maybe<sem::Type*> depth_texture_type();
+  /// Parses a 'texture_external_type' grammar element
+  /// @returns the parsed Type or nullptr if none matched
+  Maybe<sem::Type*> external_texture_type();
   /// Parses a `image_storage_type` grammar element
   /// @param use a description of what was being parsed if an error was raised
   /// @returns returns the image format or kNone if none matched.

src/reader/wgsl/parser_impl_external_texture_type_test.cc

@@ -0,0 +1,40 @@
+// Copyright 2021 The Tint Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "src/reader/wgsl/parser_impl_test_helper.h"
+
+namespace tint {
+namespace reader {
+namespace wgsl {
+namespace {
+
+TEST_F(ParserImplTest, ExternalTextureType_Invalid) {
+  auto p = parser("1234");
+  auto t = p->external_texture_type();
+  EXPECT_FALSE(t.matched);
+  EXPECT_FALSE(t.errored);
+  EXPECT_FALSE(p->has_error());
+}
+
+TEST_F(ParserImplTest, ExternalTextureType) {
+  auto p = parser("texture_external");
+  auto t = p->external_texture_type();
+  EXPECT_TRUE(t.matched);
+  EXPECT_FALSE(t.errored);
+}
+
+}  // namespace
+}  // namespace wgsl
+}  // namespace reader
+}  // namespace tint

src/reader/wgsl/token.cc

@@ -269,6 +269,8 @@ std::string Token::TypeToName(Type type) {
       return "texture_depth_cube";
     case Token::Type::kTextureDepthCubeArray:
       return "texture_depth_cube_array";
+    case Token::Type::kTextureExternal:
+      return "texture_external";
     case Token::Type::kTextureMultisampled2d:
       return "texture_multisampled_2d";
     case Token::Type::kTextureSampled1d:

src/reader/wgsl/token.h

@@ -277,6 +277,8 @@ class Token {
     kTextureDepthCube,
     /// A 'texture_depth_cube_array'
     kTextureDepthCubeArray,
+    /// A 'texture_external'
+    kTextureExternal,
     /// A 'texture_multisampled_2d'
     kTextureMultisampled2d,
     /// A 'texture_1d'