[tint] Allow read-only storage textures

Iff the chromium_experimental_read_write_storage_texture extension is
enabled.

Bug: tint:2007
Change-Id: Ic76c22b3d88d0b76253f9a0ed7b0befcd498ca0f
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/146960
Reviewed-by: Ben Clayton <[email protected]>
Kokoro: Kokoro <[email protected]>

Author: jrprice

src/tint/lang/wgsl/resolver/type_validation_test.cc

@@ -1143,7 +1143,19 @@ TEST_F(StorageTextureAccessTest, MissingAccess_Fail) {
     EXPECT_EQ(r()->error(), R"(12:34 error: 'texture_storage_1d' requires 2 template arguments)");
 }
 
-TEST_F(StorageTextureAccessTest, ReadOnlyAccess_Fail) {
+TEST_F(StorageTextureAccessTest, WriteOnlyAccess_Pass) {
+    // @group(0) @binding(0)
+    // var a : texture_storage_1d<r32uint, write>;
+
+    auto st = ty.storage_texture(core::type::TextureDimension::k1d, core::TexelFormat::kR32Uint,
+                                 core::Access::kWrite);
+
+    GlobalVar("a", st, Group(0_a), Binding(0_a));
+
+    EXPECT_TRUE(r()->Resolve()) << r()->error();
+}
+
+TEST_F(StorageTextureAccessTest, ReadOnlyAccess_WithoutExtension_Fail) {
     // @group(0) @binding(0)
     // var a : texture_storage_1d<r32uint, read>;
 
@@ -1154,15 +1166,18 @@ TEST_F(StorageTextureAccessTest, ReadOnlyAccess_Fail) {
 
     EXPECT_FALSE(r()->Resolve());
     EXPECT_EQ(r()->error(),
-              "12:34 error: storage textures currently only support 'write' access control");
+              "12:34 error: read-only storage textures require the "
+              "chromium_experimental_read_write_storage_texture extension to be enabled");
 }
 
-TEST_F(StorageTextureAccessTest, WriteOnlyAccess_Pass) {
+TEST_F(StorageTextureAccessTest, ReadOnlyAccess_WithExtension_Pass) {
+    // enable chromium_experimental_read_write_storage_texture;
     // @group(0) @binding(0)
-    // var a : texture_storage_1d<r32uint, write>;
+    // var a : texture_storage_1d<r32uint, read>;
 
-    auto st = ty.storage_texture(core::type::TextureDimension::k1d, core::TexelFormat::kR32Uint,
-                                 core::Access::kWrite);
+    Enable(core::Extension::kChromiumExperimentalReadWriteStorageTexture);
+    auto st = ty.storage_texture(Source{{12, 34}}, core::type::TextureDimension::k1d,
+                                 core::TexelFormat::kR32Uint, core::Access::kRead);
 
     GlobalVar("a", st, Group(0_a), Binding(0_a));
 

src/tint/lang/wgsl/resolver/validator.cc

@@ -312,6 +312,16 @@ bool Validator::Pointer(const ast::TemplatedIdentifier* a, const core::type::Poi
 
 bool Validator::StorageTexture(const core::type::StorageTexture* t, const Source& source) const {
     switch (t->access()) {
+        case core::Access::kRead:
+            if (!enabled_extensions_.Contains(
+                    core::Extension::kChromiumExperimentalReadWriteStorageTexture)) {
+                AddError(
+                    "read-only storage textures require the "
+                    "chromium_experimental_read_write_storage_texture extension to be enabled",
+                    source);
+                return false;
+            }
+            break;
         case core::Access::kReadWrite:
             if (!enabled_extensions_.Contains(
                     core::Extension::kChromiumExperimentalReadWriteStorageTexture)) {
@@ -327,9 +337,6 @@ bool Validator::StorageTexture(const core::type::StorageTexture* t, const Source
         case core::Access::kUndefined:
             AddError("storage texture missing access control", source);
             return false;
-        default:
-            AddError("storage textures currently only support 'write' access control", source);
-            return false;
     }
 
     if (!IsValidStorageTextureDimension(t->dim())) {