parser: fix wgsl expect_const_expr()

Bug: tint:1025
Change-Id: I35aab866ffce57681662f59e4b8e701bb03cf718
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/59220
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>
Commit-Queue: Sarah Mashayekhi <sarahmashay@google.com>

src/reader/wgsl/parser_impl.cc

@@ -2843,13 +2843,22 @@ Maybe<ast::Literal*> ParserImpl::const_literal() {
 //   | const_literal
 Expect<ast::ConstructorExpression*> ParserImpl::expect_const_expr() {
   auto t = peek();
-
   auto source = t.source();
+  if (t.IsLiteral()) {
+    auto lit = const_literal();
+    if (lit.errored)
+      return Failure::kErrored;
+    if (!lit.matched)
+      return add_error(peek(), "unable to parse constant literal");
 
-  auto type = type_decl();
+    return create<ast::ScalarConstructorExpression>(source, lit.value);
+  } else if (!t.IsIdentifier() || get_type(t.to_str())) {
+    if (peek_is(Token::Type::kParenLeft, 1) ||
+        peek_is(Token::Type::kLessThan, 1)) {
+      auto type = expect_type("const_expr");
       if (type.errored)
         return Failure::kErrored;
-  if (type.matched) {
+
       auto params = expect_paren_block(
           "type constructor", [&]() -> Expect<ast::ExpressionList> {
             ast::ExpressionList list;
@@ -2877,14 +2886,8 @@ Expect<ast::ConstructorExpression*> ParserImpl::expect_const_expr() {
       return create<ast::TypeConstructorExpression>(source, type.value,
                                                     params.value);
     }
-
+  }
-  auto lit = const_literal();
+  return add_error(peek(), "unable to parse const_expr");
-  if (lit.errored)
-    return Failure::kErrored;
-  if (!lit.matched)
-    return add_error(peek(), "unable to parse constant literal");
-
-  return create<ast::ScalarConstructorExpression>(source, lit.value);
 }
 
 Maybe<ast::DecorationList> ParserImpl::decoration_list() {

src/reader/wgsl/parser_impl_const_expr_test.cc

@@ -112,7 +112,7 @@ TEST_F(ParserImplTest, ConstExpr_InvalidExpr) {
   ASSERT_TRUE(p->has_error());
   ASSERT_TRUE(e.errored);
   ASSERT_EQ(e.value, nullptr);
-  EXPECT_EQ(p->error(), "1:15: unable to parse constant literal");
+  EXPECT_EQ(p->error(), "1:15: invalid type for const_expr");
 }
 
 TEST_F(ParserImplTest, ConstExpr_ConstLiteral) {
@@ -134,7 +134,29 @@ TEST_F(ParserImplTest, ConstExpr_ConstLiteral_Invalid) {
   ASSERT_TRUE(p->has_error());
   ASSERT_TRUE(e.errored);
   ASSERT_EQ(e.value, nullptr);
-  EXPECT_EQ(p->error(), "1:1: unknown type 'invalid'");
+  EXPECT_EQ(p->error(), "1:1: unable to parse const_expr");
+}
+
+TEST_F(ParserImplTest, ConstExpr_RegisteredType) {
+  auto p = parser("S(0)");
+
+  auto* mem = Member("m", ty.i32(), ast::DecorationList{});
+  auto* s = Structure(Sym("S"), {mem});
+  p->register_type("S", s);
+
+  auto e = p->expect_const_expr();
+  ASSERT_FALSE(e.errored);
+  ASSERT_TRUE(e->Is<ast::ConstructorExpression>());
+  ASSERT_TRUE(e->Is<ast::TypeConstructorExpression>());
+}
+
+TEST_F(ParserImplTest, ConstExpr_NotRegisteredType) {
+  auto p = parser("S(0)");
+  auto e = p->expect_const_expr();
+  ASSERT_TRUE(p->has_error());
+  ASSERT_TRUE(e.errored);
+  ASSERT_EQ(e.value, nullptr);
+  EXPECT_EQ(p->error(), "1:1: unable to parse const_expr");
 }
 
 TEST_F(ParserImplTest, ConstExpr_Recursion) {

src/reader/wgsl/parser_impl_error_msg_test.cc

@@ -434,7 +434,7 @@ TEST_F(ParserImplErrorTest, FunctionMissingOpenLine) {
   var a : f32 = bar[0];
   return;
 })",
-         "test.wgsl:2:17 error: unknown type 'bar'\n"
+         "test.wgsl:2:17 error: unable to parse const_expr\n"
          "  var a : f32 = bar[0];\n"
          "                ^^^\n"
          "\n"
@@ -473,11 +473,43 @@ TEST_F(ParserImplErrorTest, GlobalDeclConstMissingRParen) {
 
 TEST_F(ParserImplErrorTest, GlobalDeclConstBadConstLiteral) {
   EXPECT("let i : vec2<i32> = vec2<i32>(!);",
-         "test.wgsl:1:31 error: unable to parse constant literal\n"
+         "test.wgsl:1:31 error: unable to parse const_expr\n"
          "let i : vec2<i32> = vec2<i32>(!);\n"
          "                              ^\n");
 }
 
+TEST_F(ParserImplErrorTest, GlobalDeclConstBadConstLiteralSpaceLessThan) {
+  EXPECT("let i = 1 < 2;",
+         "test.wgsl:1:11 error: expected \';\' for let declaration\n"
+         "let i = 1 < 2;\n"
+         "          ^\n");
+}
+
+TEST_F(ParserImplErrorTest, GlobalDeclConstNotConstExpr) {
+  EXPECT(
+      "let a = 1;\n"
+      "let b = a;",
+      "test.wgsl:2:9 error: unable to parse const_expr\n"
+      "let b = a;\n"
+      "        ^\n");
+}
+
+TEST_F(ParserImplErrorTest, GlobalDeclConstNotConstExprWithParn) {
+  EXPECT(
+      "let a = 1;\n"
+      "let b = a();",
+      "test.wgsl:2:9 error: unable to parse const_expr\n"
+      "let b = a();\n"
+      "        ^\n");
+}
+
+TEST_F(ParserImplErrorTest, GlobalDeclConstConstExprRegisteredType) {
+  EXPECT("let a = S0(0);",
+         "test.wgsl:1:9 error: unable to parse const_expr\n"
+         "let a = S0(0);\n"
+         "        ^^\n");
+}
+
 TEST_F(ParserImplErrorTest, GlobalDeclConstExprMaxDepth) {
   uint32_t kMaxDepth = 128;
 

src/reader/wgsl/parser_impl_global_constant_decl_test.cc

@@ -98,7 +98,7 @@ TEST_F(ParserImplTest, GlobalConstantDecl_InvalidExpression) {
   EXPECT_TRUE(e.errored);
   EXPECT_FALSE(e.matched);
   EXPECT_EQ(e.value, nullptr);
-  EXPECT_EQ(p->error(), "1:15: unable to parse constant literal");
+  EXPECT_EQ(p->error(), "1:15: invalid type for const_expr");
 }
 
 TEST_F(ParserImplTest, GlobalConstantDecl_MissingExpression) {
@@ -111,7 +111,7 @@ TEST_F(ParserImplTest, GlobalConstantDecl_MissingExpression) {
   EXPECT_TRUE(e.errored);
   EXPECT_FALSE(e.matched);
   EXPECT_EQ(e.value, nullptr);
-  EXPECT_EQ(p->error(), "1:14: unable to parse constant literal");
+  EXPECT_EQ(p->error(), "1:14: unable to parse const_expr");
 }
 
 TEST_F(ParserImplTest, GlobalConstantDec_Override_WithId) {

src/reader/wgsl/parser_impl_global_variable_decl_test.cc

@@ -152,7 +152,7 @@ TEST_F(ParserImplTest, GlobalVariableDecl_InvalidConstExpr) {
   EXPECT_TRUE(e.errored);
   EXPECT_FALSE(e.matched);
   EXPECT_EQ(e.value, nullptr);
-  EXPECT_EQ(p->error(), "1:24: unable to parse constant literal");
+  EXPECT_EQ(p->error(), "1:24: invalid type for const_expr");
 }
 
 TEST_F(ParserImplTest, GlobalVariableDecl_InvalidVariableDecl) {

src/reader/wgsl/token.h

@@ -372,7 +372,12 @@ class Token {
   bool IsEof() const { return type_ == Type::kEOF; }
   /// @returns true if the token is an identifier
   bool IsIdentifier() const { return type_ == Type::kIdentifier; }
-
+  /// @returns true if the token is a literal
+  bool IsLiteral() const {
+    return type_ == Type::kSintLiteral || type_ == Type::kFalse ||
+           type_ == Type::kUintLiteral || type_ == Type::kTrue ||
+           type_ == Type::kFloatLiteral;
+  }
   /// @returns true if token is a 'matNxM'
   bool IsMatrix() const {
     return type_ == Type::kMat2x2 || type_ == Type::kMat2x3 ||