Extract interpolation sample and type name parsing

This CL pulls the interpolation sample and type name parsing out
to methods to closer match the WGSL spec. This will also make it simpler
to convert to using generated parsing for these strings if desired.

Bug: tint:1633
Change-Id: Ib7b663a3eeef7f3ecacae8bf160d41641b5474f1
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/98260
Reviewed-by: Antonio Maiorano <amaiorano@google.com>
Commit-Queue: Dan Sinclair <dsinclair@chromium.org>
Kokoro: Kokoro <noreply+kokoro@google.com>

src/tint/reader/wgsl/parser_impl.cc

@@ -1558,6 +1558,64 @@ Expect<ast::PipelineStage> ParserImpl::expect_pipeline_stage() {
     return add_error(peek(), "invalid value for stage attribute");
 }
 
+// interpolation_sample_name
+//   :  'center'
+//   | 'centroid'
+//   | 'sample'
+Expect<ast::InterpolationSampling> ParserImpl::expect_interpolation_sample_name() {
+    auto ident = expect_ident("interpolation sample name");
+    if (ident.errored) {
+        return Failure::kErrored;
+    }
+
+    if (ident.value == "center") {
+        return {ast::InterpolationSampling::kCenter, ident.source};
+    }
+    if (ident.value == "centroid") {
+        return {ast::InterpolationSampling::kCentroid, ident.source};
+    }
+    if (ident.value == "sample") {
+        return {ast::InterpolationSampling::kSample, ident.source};
+    }
+    return add_error(ident.source, "invalid interpolation sampling");
+}
+
+// interpolation_type_name
+//   : 'perspective'
+//   | 'linear'
+//   | 'flat'
+Expect<ast::InterpolationType> ParserImpl::expect_interpolation_type_name() {
+    auto ident = expect_ident("interpolation type name");
+    if (ident.errored) {
+        return Failure::kErrored;
+    }
+
+    if (ident.value == "perspective") {
+        return {ast::InterpolationType::kPerspective, ident.source};
+    }
+    if (ident.value == "linear") {
+        return {ast::InterpolationType::kLinear, ident.source};
+    }
+    if (ident.value == "flat") {
+        return {ast::InterpolationType::kFlat, ident.source};
+    }
+
+    return add_error(ident.source, "invalid interpolation type");
+}
+
+// builtin_value_name
+//   : 'vertex_index'
+//   | 'instance_index'
+//   | 'position'
+//   | 'front_facing'
+//   | 'frag_depth'
+//   | 'local_invocation_id'
+//   | 'local_invocation_index'
+//   | 'global_invocation_id'
+//   | 'workgroup_id'
+//   | 'num_workgroups'
+//   | 'sample_index'
+//   | 'sample_mask'
 Expect<ast::BuiltinValue> ParserImpl::expect_builtin() {
     auto ident = expect_ident("builtin");
     if (ident.errored) {
@@ -2995,8 +3053,8 @@ Maybe<const ast::Expression*> ParserImpl::expression() {
     return logical_or_expression();
 }
 
-// compound_assignment_operator:
+// compound_assignment_operator
-// | plus_equal
+//   : plus_equal
 //   | minus_equal
 //   | times_equal
 //   | division_equal
@@ -3234,37 +3292,25 @@ Maybe<const ast::Attribute*> ParserImpl::attribute() {
 
     if (t == kInterpolateAttribute) {
         return expect_paren_block("interpolate attribute", [&]() -> Result {
-            ast::InterpolationType type;
+            auto type = expect_interpolation_type_name();
-            ast::InterpolationSampling sampling = ast::InterpolationSampling::kNone;
+            if (type.errored) {
-
+                return Failure::kErrored;
-            auto& type_tok = next();
-            if (type_tok == "perspective") {
-                type = ast::InterpolationType::kPerspective;
-            } else if (type_tok == "linear") {
-                type = ast::InterpolationType::kLinear;
-            } else if (type_tok == "flat") {
-                type = ast::InterpolationType::kFlat;
-            } else {
-                return add_error(type_tok, "invalid interpolation type");
             }
 
+            ast::InterpolationSampling sampling = ast::InterpolationSampling::kNone;
             if (match(Token::Type::kComma)) {
                 if (!peek_is(Token::Type::kParenRight)) {
-                    auto& sampling_tok = next();
+                    auto sample = expect_interpolation_sample_name();
-                    if (sampling_tok == "center") {
+                    if (sample.errored) {
-                        sampling = ast::InterpolationSampling::kCenter;
+                        return Failure::kErrored;
-                    } else if (sampling_tok == "centroid") {
-                        sampling = ast::InterpolationSampling::kCentroid;
-                    } else if (sampling_tok == "sample") {
-                        sampling = ast::InterpolationSampling::kSample;
-                    } else {
-                        return add_error(sampling_tok, "invalid interpolation sampling");
                     }
+
+                    sampling = sample.value;
                     match(Token::Type::kComma);
                 }
             }
 
-            return create<ast::InterpolateAttribute>(t.source(), type, sampling);
+            return create<ast::InterpolateAttribute>(t.source(), type.value, sampling);
         });
     }
 

src/tint/reader/wgsl/parser_impl.h

@@ -493,6 +493,14 @@ class ParserImpl {
     /// @param use a description of what was being parsed if an error was raised
     /// @returns the parsed access control.
     Expect<ast::Access> expect_access(std::string_view use);
+    /// Parses an interpolation sample name identifier, erroring if the next token does not match a
+    /// valid sample name.
+    /// @returns the parsed sample name.
+    Expect<ast::InterpolationSampling> expect_interpolation_sample_name();
+    /// Parses an interpolation type name identifier, erroring if the next token does not match a
+    /// value type name.
+    /// @returns the parsed type name
+    Expect<ast::InterpolationType> expect_interpolation_type_name();
     /// Parses a builtin identifier, erroring if the next token does not match a
     /// valid builtin name.
     /// @returns the parsed builtin.

src/tint/reader/wgsl/parser_impl_variable_attribute_test.cc

@@ -235,7 +235,7 @@ TEST_F(ParserImplTest, Attribute_Interpolate_Single_DoubleTrailingComma) {
     EXPECT_TRUE(attr.errored);
     EXPECT_EQ(attr.value, nullptr);
     EXPECT_TRUE(p->has_error());
-    EXPECT_EQ(p->error(), "1:18: invalid interpolation sampling");
+    EXPECT_EQ(p->error(), "1:18: expected identifier for interpolation sample name");
 }
 
 TEST_F(ParserImplTest, Attribute_Interpolate_Perspective_Center) {
@@ -329,7 +329,7 @@ TEST_F(ParserImplTest, Attribute_Interpolate_MissingFirstValue) {
     EXPECT_TRUE(attr.errored);
     EXPECT_EQ(attr.value, nullptr);
     EXPECT_TRUE(p->has_error());
-    EXPECT_EQ(p->error(), "1:13: invalid interpolation type");
+    EXPECT_EQ(p->error(), "1:13: expected identifier for interpolation type name");
 }
 
 TEST_F(ParserImplTest, Attribute_Interpolate_InvalidFirstValue) {