Add `element_count_expression` to WGSL parser

This CL adds the `element_count_expression` and the requisite math
expression parsing to support along with tests.

Bug: tint:1633

Change-Id: I54ab37339754217f417f69dcd6140adbc14cbf83
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/99560
Reviewed-by: Ben Clayton <bclayton@google.com>
Commit-Queue: Dan Sinclair <dsinclair@chromium.org>
Kokoro: Kokoro <noreply+kokoro@google.com>

src/tint/BUILD.gn

@@ -1364,6 +1364,7 @@ if (tint_build_unittests) {
       "reader/wgsl/parser_impl_continuing_stmt_test.cc",
       "reader/wgsl/parser_impl_core_lhs_expression_test.cc",
       "reader/wgsl/parser_impl_depth_texture_test.cc",
+      "reader/wgsl/parser_impl_element_count_expression_test.cc",
       "reader/wgsl/parser_impl_enable_directive_test.cc",
       "reader/wgsl/parser_impl_equality_expression_test.cc",
       "reader/wgsl/parser_impl_error_msg_test.cc",
@@ -1385,6 +1386,7 @@ if (tint_build_unittests) {
       "reader/wgsl/parser_impl_logical_and_expression_test.cc",
       "reader/wgsl/parser_impl_logical_or_expression_test.cc",
       "reader/wgsl/parser_impl_loop_stmt_test.cc",
+      "reader/wgsl/parser_impl_math_expression_test.cc",
       "reader/wgsl/parser_impl_multiplicative_expression_test.cc",
       "reader/wgsl/parser_impl_param_list_test.cc",
       "reader/wgsl/parser_impl_paren_expression_test.cc",

src/tint/CMakeLists.txt

@@ -959,6 +959,7 @@ if(TINT_BUILD_TESTS)
       reader/wgsl/parser_impl_continuing_stmt_test.cc
       reader/wgsl/parser_impl_core_lhs_expression_test.cc
       reader/wgsl/parser_impl_depth_texture_test.cc
+      reader/wgsl/parser_impl_element_count_expression_test.cc
       reader/wgsl/parser_impl_enable_directive_test.cc
       reader/wgsl/parser_impl_external_texture_test.cc
       reader/wgsl/parser_impl_equality_expression_test.cc
@@ -980,6 +981,7 @@ if(TINT_BUILD_TESTS)
       reader/wgsl/parser_impl_logical_and_expression_test.cc
       reader/wgsl/parser_impl_logical_or_expression_test.cc
       reader/wgsl/parser_impl_loop_stmt_test.cc
+      reader/wgsl/parser_impl_math_expression_test.cc
       reader/wgsl/parser_impl_multiplicative_expression_test.cc
       reader/wgsl/parser_impl_param_list_test.cc
       reader/wgsl/parser_impl_paren_expression_test.cc

src/tint/reader/wgsl/lexer_test.cc

@@ -1028,7 +1028,6 @@ INSTANTIATE_TEST_SUITE_P(LexerTest,
                                          TokenData{"%", Token::Type::kMod},
                                          TokenData{"!=", Token::Type::kNotEqual},
                                          TokenData{"-", Token::Type::kMinus},
-                                         TokenData{"--", Token::Type::kMinusMinus},
                                          TokenData{".", Token::Type::kPeriod},
                                          TokenData{"+", Token::Type::kPlus},
                                          TokenData{"++", Token::Type::kPlusPlus},
@@ -1088,6 +1087,7 @@ INSTANTIATE_TEST_SUITE_P(LexerTest,
                          SplittablePunctuationTest,
                          testing::Values(TokenData{"&&", Token::Type::kAndAnd},
                                          TokenData{">=", Token::Type::kGreaterThanEqual},
+                                         TokenData{"--", Token::Type::kMinusMinus},
                                          TokenData{">>", Token::Type::kShiftRight}));
 
 using KeywordTest = testing::TestWithParam<TokenData>;

src/tint/reader/wgsl/parser_impl.cc

@@ -1066,7 +1066,7 @@ Maybe<const ast::Alias*> ParserImpl::type_alias_decl() {
 //   | VEC3 LESS_THAN type_decl GREATER_THAN
 //   | VEC4 LESS_THAN type_decl GREATER_THAN
 //   | PTR LESS_THAN storage_class, type_decl (COMMA access_mode)? GREATER_THAN
-//   | array_attribute_list* ARRAY LESS_THAN type_decl COMMA INT_LITERAL GREATER_THAN
+//   | array_attribute_list* ARRAY LESS_THAN type_decl COMMA element_count_expression GREATER_THAN
 //   | array_attribute_list* ARRAY LESS_THAN type_decl GREATER_THAN
 //   | MAT2x2 LESS_THAN type_decl GREATER_THAN
 //   | MAT2x3 LESS_THAN type_decl GREATER_THAN
@@ -1244,10 +1244,11 @@ Expect<const ast::Type*> ParserImpl::expect_type_decl_array(const Token& t) {
             return TypeAndSize{type.value, nullptr};
         }
 
-        auto size = primary_expression();
+        auto size = element_count_expression();
         if (size.errored) {
             return Failure::kErrored;
-        } else if (!size.matched) {
+        }
+        if (!size.matched) {
             return add_error(peek(), "expected array size expression");
         }
 
@@ -2657,6 +2658,162 @@ Maybe<const ast::Expression*> ParserImpl::bitwise_expression_post_unary_expressi
     return Failure::kErrored;
 }
 
+// multiplicative_operator
+//   : FORWARD_SLASH
+//   | MODULO
+//   | STAR
+Maybe<ast::BinaryOp> ParserImpl::multiplicative_operator() {
+    if (match(Token::Type::kForwardSlash)) {
+        return ast::BinaryOp::kDivide;
+    }
+    if (match(Token::Type::kMod)) {
+        return ast::BinaryOp::kModulo;
+    }
+    if (match(Token::Type::kStar)) {
+        return ast::BinaryOp::kMultiply;
+    }
+
+    return Failure::kNoMatch;
+}
+
+// multiplicative_expression.post.unary_expression
+//   : (multiplicative_operator unary_expression)*
+Expect<const ast::Expression*> ParserImpl::expect_multiplicative_expression_post_unary_expression(
+    const ast::Expression* lhs) {
+    while (continue_parsing()) {
+        auto& t = peek();
+
+        auto op = multiplicative_operator();
+        if (op.errored) {
+            return Failure::kErrored;
+        }
+        if (!op.matched) {
+            return lhs;
+        }
+
+        auto rhs = unary_expression();
+        if (rhs.errored) {
+            return Failure::kErrored;
+        }
+        if (!rhs.matched) {
+            return add_error(peek(), std::string("unable to parse right side of ") +
+                                         std::string(t.to_name()) + " expression");
+        }
+
+        lhs = create<ast::BinaryExpression>(t.source(), op.value, lhs, rhs.value);
+    }
+    return Failure::kErrored;
+}
+
+// additive_operator
+//   : MINUS
+//   | PLUS
+//
+// Note, this also splits a `--` token. This is currently safe as the only way to get into
+// here is through additive expression and rules for where `--` are allowed are very restrictive.
+Maybe<ast::BinaryOp> ParserImpl::additive_operator() {
+    if (match(Token::Type::kPlus)) {
+        return ast::BinaryOp::kAdd;
+    }
+
+    auto& t = peek();
+    if (t.Is(Token::Type::kMinusMinus)) {
+        next();
+        split_token(Token::Type::kMinus, Token::Type::kMinus);
+    } else if (t.Is(Token::Type::kMinus)) {
+        next();
+    } else {
+        return Failure::kNoMatch;
+    }
+
+    return ast::BinaryOp::kSubtract;
+}
+
+// additive_expression.pos.unary_expression
+//   : (additive_operator unary_expression expect_multiplicative_expression.post.unary_expression)*
+//
+// This is `( additive_operator unary_expression ( multiplicative_operator unary_expression )* )*`
+// split apart.
+Expect<const ast::Expression*> ParserImpl::expect_additive_expression_post_unary_expression(
+    const ast::Expression* lhs) {
+    while (continue_parsing()) {
+        auto& t = peek();
+
+        auto op = additive_operator();
+        if (op.errored) {
+            return Failure::kErrored;
+        }
+        if (!op.matched) {
+            return lhs;
+        }
+
+        auto unary = unary_expression();
+        if (unary.errored) {
+            return Failure::kErrored;
+        }
+        if (!unary.matched) {
+            return add_error(peek(), std::string("unable to parse right side of ") +
+                                         std::string(t.to_name()) + " expression");
+        }
+
+        // The multiplicative binds tigher, so pass the unary into that and build that expression
+        // before creating the additve expression.
+        auto rhs = expect_multiplicative_expression_post_unary_expression(unary.value);
+        if (rhs.errored) {
+            return Failure::kErrored;
+        }
+
+        lhs = create<ast::BinaryExpression>(t.source(), op.value, lhs, rhs.value);
+    }
+    return Failure::kErrored;
+}
+
+// math_expression.post.unary_expression
+//   : multiplicative_expression.post.unary_expression additive_expression.post.unary_expression
+//
+// This is `( multiplicative_operator unary_expression )* ( additive_operator unary_expression (
+// multiplicative_operator unary_expression )* )*` split apart.
+Expect<const ast::Expression*> ParserImpl::expect_math_expression_post_unary_expression(
+    const ast::Expression* lhs) {
+    auto rhs = expect_multiplicative_expression_post_unary_expression(lhs);
+    if (rhs.errored) {
+        return Failure::kErrored;
+    }
+
+    return expect_additive_expression_post_unary_expression(rhs.value);
+}
+
+// element_count_expression
+//   : unary_expression math_expression.post.unary_expression
+//   | unary_expression bitwise_expression.post.unary_expression
+//
+// Note, this moves the `( multiplicative_operator unary_expression )* ( additive_operator
+// unary_expression ( multiplicative_operator unary_expression )* )*` expression for the first
+// branch out into helper methods.
+Maybe<const ast::Expression*> ParserImpl::element_count_expression() {
+    auto lhs = unary_expression();
+    if (lhs.errored) {
+        return Failure::kErrored;
+    }
+    if (!lhs.matched) {
+        return Failure::kNoMatch;
+    }
+
+    auto bitwise = bitwise_expression_post_unary_expression(lhs.value);
+    if (bitwise.errored) {
+        return Failure::kErrored;
+    }
+    if (bitwise.matched) {
+        return bitwise.value;
+    }
+
+    auto math = expect_math_expression_post_unary_expression(lhs.value);
+    if (math.errored) {
+        return Failure::kErrored;
+    }
+    return math.value;
+}
+
 // unary_expression
 //   : singular_expression
 //   | MINUS unary_expression

src/tint/reader/wgsl/parser_impl.h

@@ -646,6 +646,30 @@ class ParserImpl {
     /// @returns the parsed expression or nullptr
     Maybe<const ast::Expression*> bitwise_expression_post_unary_expression(
         const ast::Expression* lhs);
+    /// Parse the `multiplicative_operator` grammar element
+    /// @returns the parsed operator if successful
+    Maybe<ast::BinaryOp> multiplicative_operator();
+    /// Parses multiplicative elements
+    /// @param lhs the left side of the expression
+    /// @returns the parsed expression or `lhs` if no match
+    Expect<const ast::Expression*> expect_multiplicative_expression_post_unary_expression(
+        const ast::Expression* lhs);
+    /// Parses additive elements
+    /// @param lhs the left side of the expression
+    /// @returns the parsed expression or `lhs` if no match
+    Expect<const ast::Expression*> expect_additive_expression_post_unary_expression(
+        const ast::Expression* lhs);
+    /// Parses math elements
+    /// @param lhs the left side of the expression
+    /// @returns the parsed expression or `lhs` if no match
+    Expect<const ast::Expression*> expect_math_expression_post_unary_expression(
+        const ast::Expression* lhs);
+    /// Parses an `element_count_expression` grammar element
+    /// @returns the parsed expression or nullptr
+    Maybe<const ast::Expression*> element_count_expression();
+    /// Parse the `additive_operator` grammar element
+    /// @returns the parsed operator if successful
+    Maybe<ast::BinaryOp> additive_operator();
     /// Parses the recursive part of the `and_expression`, erroring on parse
     /// failure.
     /// @param lhs the left side of the expression

src/tint/reader/wgsl/parser_impl_additive_expression_test.cc

@@ -17,7 +17,7 @@
 namespace tint::reader::wgsl {
 namespace {
 
-TEST_F(ParserImplTest, AdditiveExpression_Parses_Plus) {
+TEST_F(ParserImplTest, AdditiveExpression_Orig_Parses_Plus) {
     auto p = parser("a + true");
     auto e = p->additive_expression();
     EXPECT_TRUE(e.matched);
@@ -42,7 +42,7 @@ TEST_F(ParserImplTest, AdditiveExpression_Parses_Plus) {
     ASSERT_TRUE(rel->rhs->As<ast::BoolLiteralExpression>()->value);
 }
 
-TEST_F(ParserImplTest, AdditiveExpression_Parses_Minus) {
+TEST_F(ParserImplTest, AdditiveExpression_Orig_Parses_Minus) {
     auto p = parser("a - true");
     auto e = p->additive_expression();
     EXPECT_TRUE(e.matched);
@@ -62,7 +62,7 @@ TEST_F(ParserImplTest, AdditiveExpression_Parses_Minus) {
     ASSERT_TRUE(rel->rhs->As<ast::BoolLiteralExpression>()->value);
 }
 
-TEST_F(ParserImplTest, AdditiveExpression_InvalidLHS) {
+TEST_F(ParserImplTest, AdditiveExpression_Orig_InvalidLHS) {
     auto p = parser("if (a) {} + true");
     auto e = p->additive_expression();
     EXPECT_FALSE(e.matched);
@@ -71,7 +71,7 @@ TEST_F(ParserImplTest, AdditiveExpression_InvalidLHS) {
     EXPECT_EQ(e.value, nullptr);
 }
 
-TEST_F(ParserImplTest, AdditiveExpression_InvalidRHS) {
+TEST_F(ParserImplTest, AdditiveExpression_Orig_InvalidRHS) {
     auto p = parser("true + if (a) {}");
     auto e = p->additive_expression();
     EXPECT_FALSE(e.matched);
@@ -81,7 +81,7 @@ TEST_F(ParserImplTest, AdditiveExpression_InvalidRHS) {
     EXPECT_EQ(p->error(), "1:8: unable to parse right side of + expression");
 }
 
-TEST_F(ParserImplTest, AdditiveExpression_NoOr_ReturnsLHS) {
+TEST_F(ParserImplTest, AdditiveExpression_Orig_NoOr_ReturnsLHS) {
     auto p = parser("a true");
     auto e = p->additive_expression();
     EXPECT_TRUE(e.matched);
@@ -91,5 +91,189 @@ TEST_F(ParserImplTest, AdditiveExpression_NoOr_ReturnsLHS) {
     ASSERT_TRUE(e->Is<ast::IdentifierExpression>());
 }
 
+TEST_F(ParserImplTest, AdditiveExpression_Parses_Plus) {
+    auto p = parser("a + b");
+    auto lhs = p->unary_expression();
+    auto e = p->expect_additive_expression_post_unary_expression(lhs.value);
+    EXPECT_FALSE(e.errored);
+    EXPECT_FALSE(p->has_error()) << p->error();
+    ASSERT_NE(e.value, nullptr);
+
+    EXPECT_EQ(e->source.range.begin.line, 1u);
+    EXPECT_EQ(e->source.range.begin.column, 3u);
+    EXPECT_EQ(e->source.range.end.line, 1u);
+    EXPECT_EQ(e->source.range.end.column, 4u);
+
+    ASSERT_TRUE(e->Is<ast::BinaryExpression>());
+    auto* rel = e->As<ast::BinaryExpression>();
+    EXPECT_EQ(ast::BinaryOp::kAdd, rel->op);
+
+    ASSERT_TRUE(rel->lhs->Is<ast::IdentifierExpression>());
+    auto* ident = rel->lhs->As<ast::IdentifierExpression>();
+    EXPECT_EQ(ident->symbol, p->builder().Symbols().Get("a"));
+
+    ASSERT_TRUE(rel->rhs->Is<ast::IdentifierExpression>());
+    ident = rel->rhs->As<ast::IdentifierExpression>();
+    EXPECT_EQ(ident->symbol, p->builder().Symbols().Get("b"));
+}
+
+TEST_F(ParserImplTest, AdditiveExpression_Parses_Minus) {
+    auto p = parser("a - b");
+    auto lhs = p->unary_expression();
+    auto e = p->expect_additive_expression_post_unary_expression(lhs.value);
+    EXPECT_FALSE(e.errored);
+    EXPECT_FALSE(p->has_error()) << p->error();
+    ASSERT_NE(e.value, nullptr);
+
+    ASSERT_TRUE(e->Is<ast::BinaryExpression>());
+    auto* rel = e->As<ast::BinaryExpression>();
+    EXPECT_EQ(ast::BinaryOp::kSubtract, rel->op);
+
+    ASSERT_TRUE(rel->lhs->Is<ast::IdentifierExpression>());
+    auto* ident = rel->lhs->As<ast::IdentifierExpression>();
+    EXPECT_EQ(ident->symbol, p->builder().Symbols().Get("a"));
+
+    ASSERT_TRUE(rel->rhs->Is<ast::IdentifierExpression>());
+    ident = rel->rhs->As<ast::IdentifierExpression>();
+    EXPECT_EQ(ident->symbol, p->builder().Symbols().Get("b"));
+}
+
+TEST_F(ParserImplTest, AdditiveExpression_Parses_MinusMinus) {
+    auto p = parser("a--b");
+    auto lhs = p->unary_expression();
+    auto e = p->expect_additive_expression_post_unary_expression(lhs.value);
+    EXPECT_FALSE(e.errored);
+    EXPECT_FALSE(p->has_error()) << p->error();
+    ASSERT_NE(e.value, nullptr);
+
+    ASSERT_TRUE(e->Is<ast::BinaryExpression>());
+    auto* rel = e->As<ast::BinaryExpression>();
+    EXPECT_EQ(ast::BinaryOp::kSubtract, rel->op);
+
+    ASSERT_TRUE(rel->lhs->Is<ast::IdentifierExpression>());
+    auto* ident = rel->lhs->As<ast::IdentifierExpression>();
+    EXPECT_EQ(ident->symbol, p->builder().Symbols().Get("a"));
+
+    ASSERT_TRUE(rel->rhs->Is<ast::UnaryOpExpression>());
+    auto* unary = rel->rhs->As<ast::UnaryOpExpression>();
+    EXPECT_EQ(ast::UnaryOp::kNegation, unary->op);
+
+    ASSERT_TRUE(unary->expr->Is<ast::IdentifierExpression>());
+    ident = unary->expr->As<ast::IdentifierExpression>();
+    EXPECT_EQ(ident->symbol, p->builder().Symbols().Get("b"));
+}
+
+TEST_F(ParserImplTest, AdditiveExpression_Parses_MultipleOps) {
+    auto p = parser("a - b + c - d");
+    auto lhs = p->unary_expression();
+    auto e = p->expect_additive_expression_post_unary_expression(lhs.value);
+    EXPECT_FALSE(e.errored);
+    EXPECT_FALSE(p->has_error()) << p->error();
+    ASSERT_NE(e.value, nullptr);
+
+    ASSERT_TRUE(e->Is<ast::BinaryExpression>());
+    // lhs: ((a - b) + c
+    // op: -
+    // rhs: d
+    auto* rel = e->As<ast::BinaryExpression>();
+    EXPECT_EQ(ast::BinaryOp::kSubtract, rel->op);
+
+    ASSERT_TRUE(rel->rhs->Is<ast::IdentifierExpression>());
+    auto* ident = rel->rhs->As<ast::IdentifierExpression>();
+    EXPECT_EQ(ident->symbol, p->builder().Symbols().Get("d"));
+
+    ASSERT_TRUE(rel->lhs->Is<ast::BinaryExpression>());
+    // lhs: a - b
+    // op: +
+    // rhs: c
+    rel = rel->lhs->As<ast::BinaryExpression>();
+    EXPECT_EQ(ast::BinaryOp::kAdd, rel->op);
+
+    ASSERT_TRUE(rel->rhs->Is<ast::IdentifierExpression>());
+    ident = rel->rhs->As<ast::IdentifierExpression>();
+    EXPECT_EQ(ident->symbol, p->builder().Symbols().Get("c"));
+
+    ASSERT_TRUE(rel->lhs->Is<ast::BinaryExpression>());
+    // lhs: a
+    // op: -
+    // rhs: b
+    rel = rel->lhs->As<ast::BinaryExpression>();
+    EXPECT_EQ(ast::BinaryOp::kSubtract, rel->op);
+
+    ASSERT_TRUE(rel->lhs->Is<ast::IdentifierExpression>());
+    ident = rel->lhs->As<ast::IdentifierExpression>();
+    EXPECT_EQ(ident->symbol, p->builder().Symbols().Get("a"));
+
+    ASSERT_TRUE(rel->rhs->Is<ast::IdentifierExpression>());
+    ident = rel->rhs->As<ast::IdentifierExpression>();
+    EXPECT_EQ(ident->symbol, p->builder().Symbols().Get("b"));
+}
+
+TEST_F(ParserImplTest, AdditiveExpression_Parses_MultipleOps_MixedMultiplication) {
+    auto p = parser("a - b * c - d");
+    auto lhs = p->unary_expression();
+    auto e = p->expect_additive_expression_post_unary_expression(lhs.value);
+    EXPECT_FALSE(e.errored);
+    EXPECT_FALSE(p->has_error()) << p->error();
+    ASSERT_NE(e.value, nullptr);
+
+    ASSERT_TRUE(e->Is<ast::BinaryExpression>());
+    // lhs: a - (b * c)
+    // op: -
+    // rhs: d
+    auto* rel = e->As<ast::BinaryExpression>();
+    EXPECT_EQ(ast::BinaryOp::kSubtract, rel->op);
+
+    ASSERT_TRUE(rel->rhs->Is<ast::IdentifierExpression>());
+    auto* ident = rel->rhs->As<ast::IdentifierExpression>();
+    EXPECT_EQ(ident->symbol, p->builder().Symbols().Get("d"));
+
+    ASSERT_TRUE(rel->lhs->Is<ast::BinaryExpression>());
+    // lhs: a
+    // op: -
+    // rhs: b * c
+    rel = rel->lhs->As<ast::BinaryExpression>();
+    EXPECT_EQ(ast::BinaryOp::kSubtract, rel->op);
+
+    ASSERT_TRUE(rel->lhs->Is<ast::IdentifierExpression>());
+    ident = rel->lhs->As<ast::IdentifierExpression>();
+    EXPECT_EQ(ident->symbol, p->builder().Symbols().Get("a"));
+
+    ASSERT_TRUE(rel->rhs->Is<ast::BinaryExpression>());
+    // lhs: b
+    // op: *
+    // rhs: c
+    rel = rel->rhs->As<ast::BinaryExpression>();
+    EXPECT_EQ(ast::BinaryOp::kMultiply, rel->op);
+
+    ASSERT_TRUE(rel->lhs->Is<ast::IdentifierExpression>());
+    ident = rel->lhs->As<ast::IdentifierExpression>();
+    EXPECT_EQ(ident->symbol, p->builder().Symbols().Get("b"));
+
+    ASSERT_TRUE(rel->rhs->Is<ast::IdentifierExpression>());
+    ident = rel->rhs->As<ast::IdentifierExpression>();
+    EXPECT_EQ(ident->symbol, p->builder().Symbols().Get("c"));
+}
+
+TEST_F(ParserImplTest, AdditiveExpression_InvalidRHS) {
+    auto p = parser("a + if (a) {}");
+    auto lhs = p->unary_expression();
+    auto e = p->expect_additive_expression_post_unary_expression(lhs.value);
+    EXPECT_TRUE(e.errored);
+    EXPECT_EQ(e.value, nullptr);
+    EXPECT_TRUE(p->has_error());
+    EXPECT_EQ(p->error(), "1:5: unable to parse right side of + expression");
+}
+
+TEST_F(ParserImplTest, AdditiveExpression_NoMatch_ReturnsLHS) {
+    auto p = parser("a true");
+    auto lhs = p->unary_expression();
+    auto e = p->expect_additive_expression_post_unary_expression(lhs.value);
+    EXPECT_FALSE(e.errored);
+    EXPECT_FALSE(p->has_error()) << p->error();
+    ASSERT_NE(e.value, nullptr);
+    EXPECT_EQ(lhs.value, e.value);
+}
+
 }  // namespace
 }  // namespace tint::reader::wgsl

src/tint/reader/wgsl/parser_impl_element_count_expression_test.cc

@@ -0,0 +1,81 @@
+// Copyright 2022 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/tint/reader/wgsl/parser_impl_test_helper.h"
+
+namespace tint::reader::wgsl {
+namespace {
+
+TEST_F(ParserImplTest, ElementCountExpression_Math) {
+    auto p = parser("a * b");
+    auto e = p->element_count_expression();
+    EXPECT_TRUE(e.matched);
+    EXPECT_FALSE(e.errored);
+    EXPECT_FALSE(p->has_error()) << p->error();
+    ASSERT_NE(e.value, nullptr);
+
+    ASSERT_TRUE(e->Is<ast::BinaryExpression>());
+    auto* rel = e->As<ast::BinaryExpression>();
+    EXPECT_EQ(ast::BinaryOp::kMultiply, rel->op);
+
+    ASSERT_TRUE(rel->lhs->Is<ast::IdentifierExpression>());
+    auto* ident = rel->lhs->As<ast::IdentifierExpression>();
+    EXPECT_EQ(ident->symbol, p->builder().Symbols().Get("a"));
+
+    ASSERT_TRUE(rel->rhs->Is<ast::IdentifierExpression>());
+    ident = rel->rhs->As<ast::IdentifierExpression>();
+    EXPECT_EQ(ident->symbol, p->builder().Symbols().Get("b"));
+}
+
+TEST_F(ParserImplTest, ElementCountExpression_Bitwise) {
+    auto p = parser("a | true");
+    auto e = p->element_count_expression();
+    EXPECT_TRUE(e.matched);
+    EXPECT_FALSE(e.errored);
+    EXPECT_FALSE(p->has_error()) << p->error();
+    ASSERT_NE(e.value, nullptr);
+
+    ASSERT_TRUE(e->Is<ast::BinaryExpression>());
+    auto* rel = e->As<ast::BinaryExpression>();
+    EXPECT_EQ(ast::BinaryOp::kOr, rel->op);
+
+    ASSERT_TRUE(rel->lhs->Is<ast::IdentifierExpression>());
+    auto* ident = rel->lhs->As<ast::IdentifierExpression>();
+    EXPECT_EQ(ident->symbol, p->builder().Symbols().Get("a"));
+
+    ASSERT_TRUE(rel->rhs->Is<ast::BoolLiteralExpression>());
+    ASSERT_TRUE(rel->rhs->As<ast::BoolLiteralExpression>()->value);
+}
+
+TEST_F(ParserImplTest, ElementCountExpression_NoMatch) {
+    auto p = parser("if (a) { }");
+    auto e = p->element_count_expression();
+    EXPECT_FALSE(e.matched);
+    EXPECT_FALSE(e.errored);
+    EXPECT_FALSE(p->has_error()) << p->error();
+    ASSERT_EQ(e.value, nullptr);
+}
+
+TEST_F(ParserImplTest, ElementCountExpression_InvalidRHS) {
+    auto p = parser("a * if");
+    auto e = p->element_count_expression();
+    EXPECT_FALSE(e.matched);
+    EXPECT_TRUE(e.errored);
+    EXPECT_TRUE(p->has_error());
+    ASSERT_EQ(e.value, nullptr);
+    EXPECT_EQ("1:5: unable to parse right side of * expression", p->error());
+}
+
+}  // namespace
+}  // namespace tint::reader::wgsl

src/tint/reader/wgsl/parser_impl_error_msg_test.cc

@@ -937,7 +937,7 @@ var i : array<u32, >;
 
 TEST_F(ParserImplErrorTest, GlobalDeclVarArrayInvalidSize) {
     EXPECT("var i : array<u32, !>;",
-           R"(test.wgsl:1:20 error: expected array size expression
+           R"(test.wgsl:1:21 error: unable to parse right side of ! expression
 var i : array<u32, !>;
                     ^
 )");

src/tint/reader/wgsl/parser_impl_math_expression_test.cc

@@ -0,0 +1,153 @@
+// Copyright 2022 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/tint/reader/wgsl/parser_impl_test_helper.h"
+
+namespace tint::reader::wgsl {
+namespace {
+
+TEST_F(ParserImplTest, MathExpression_Parses_Multiplicative) {
+    auto p = parser("a * b");
+    auto lhs = p->unary_expression();
+    auto e = p->expect_math_expression_post_unary_expression(lhs.value);
+    EXPECT_FALSE(e.errored);
+    EXPECT_FALSE(p->has_error()) << p->error();
+    ASSERT_NE(e.value, nullptr);
+
+    ASSERT_TRUE(e->Is<ast::BinaryExpression>());
+    auto* rel = e->As<ast::BinaryExpression>();
+    EXPECT_EQ(ast::BinaryOp::kMultiply, rel->op);
+
+    ASSERT_TRUE(rel->lhs->Is<ast::IdentifierExpression>());
+    auto* ident = rel->lhs->As<ast::IdentifierExpression>();
+    EXPECT_EQ(ident->symbol, p->builder().Symbols().Get("a"));
+
+    ASSERT_TRUE(rel->rhs->Is<ast::IdentifierExpression>());
+    ident = rel->rhs->As<ast::IdentifierExpression>();
+    EXPECT_EQ(ident->symbol, p->builder().Symbols().Get("b"));
+}
+
+TEST_F(ParserImplTest, MathExpression_Parses_Mixed_MultiplicativeStart) {
+    auto p = parser("a * b + c");
+    auto lhs = p->unary_expression();
+    auto e = p->expect_math_expression_post_unary_expression(lhs.value);
+    EXPECT_FALSE(e.errored);
+    EXPECT_FALSE(p->has_error()) << p->error();
+    ASSERT_NE(e.value, nullptr);
+
+    ASSERT_TRUE(e->Is<ast::BinaryExpression>());
+    // lhs: a * b
+    // op: +
+    // rhs: c
+    auto* rel = e->As<ast::BinaryExpression>();
+    EXPECT_EQ(ast::BinaryOp::kAdd, rel->op);
+
+    ASSERT_TRUE(rel->rhs->Is<ast::IdentifierExpression>());
+    auto* ident = rel->rhs->As<ast::IdentifierExpression>();
+    EXPECT_EQ(ident->symbol, p->builder().Symbols().Get("c"));
+
+    ASSERT_TRUE(rel->lhs->Is<ast::BinaryExpression>());
+    // lhs: a
+    // op: *
+    // rhs: b
+    rel = rel->lhs->As<ast::BinaryExpression>();
+    EXPECT_EQ(ast::BinaryOp::kMultiply, rel->op);
+
+    ASSERT_TRUE(rel->lhs->Is<ast::IdentifierExpression>());
+    ident = rel->lhs->As<ast::IdentifierExpression>();
+    EXPECT_EQ(ident->symbol, p->builder().Symbols().Get("a"));
+
+    ASSERT_TRUE(rel->rhs->Is<ast::IdentifierExpression>());
+    ident = rel->rhs->As<ast::IdentifierExpression>();
+    EXPECT_EQ(ident->symbol, p->builder().Symbols().Get("b"));
+}
+
+TEST_F(ParserImplTest, MathExpression_Parses_Additive) {
+    auto p = parser("a + b");
+    auto lhs = p->unary_expression();
+    auto e = p->expect_math_expression_post_unary_expression(lhs.value);
+    EXPECT_FALSE(e.errored);
+    EXPECT_FALSE(p->has_error()) << p->error();
+    ASSERT_NE(e.value, nullptr);
+
+    ASSERT_TRUE(e->Is<ast::BinaryExpression>());
+    auto* rel = e->As<ast::BinaryExpression>();
+    EXPECT_EQ(ast::BinaryOp::kAdd, rel->op);
+
+    ASSERT_TRUE(rel->lhs->Is<ast::IdentifierExpression>());
+    auto* ident = rel->lhs->As<ast::IdentifierExpression>();
+    EXPECT_EQ(ident->symbol, p->builder().Symbols().Get("a"));
+
+    ASSERT_TRUE(rel->rhs->Is<ast::IdentifierExpression>());
+    ident = rel->rhs->As<ast::IdentifierExpression>();
+    EXPECT_EQ(ident->symbol, p->builder().Symbols().Get("b"));
+}
+
+TEST_F(ParserImplTest, MathExpression_Parses_Mixed_AdditiveStart) {
+    auto p = parser("a + b * c");
+    auto lhs = p->unary_expression();
+    auto e = p->expect_math_expression_post_unary_expression(lhs.value);
+    EXPECT_FALSE(e.errored);
+    EXPECT_FALSE(p->has_error()) << p->error();
+    ASSERT_NE(e.value, nullptr);
+
+    ASSERT_TRUE(e->Is<ast::BinaryExpression>());
+    // lhs: a
+    // op: +
+    // rhs: b * c
+    auto* rel = e->As<ast::BinaryExpression>();
+    EXPECT_EQ(ast::BinaryOp::kAdd, rel->op);
+
+    ASSERT_TRUE(rel->lhs->Is<ast::IdentifierExpression>());
+    auto* ident = rel->lhs->As<ast::IdentifierExpression>();
+    EXPECT_EQ(ident->symbol, p->builder().Symbols().Get("a"));
+
+    ASSERT_TRUE(rel->rhs->Is<ast::BinaryExpression>());
+    // lhs: b
+    // op: *
+    // rhs: c
+    rel = rel->rhs->As<ast::BinaryExpression>();
+    EXPECT_EQ(ast::BinaryOp::kMultiply, rel->op);
+
+    ASSERT_TRUE(rel->lhs->Is<ast::IdentifierExpression>());
+    ident = rel->lhs->As<ast::IdentifierExpression>();
+    EXPECT_EQ(ident->symbol, p->builder().Symbols().Get("b"));
+
+    ASSERT_TRUE(rel->rhs->Is<ast::IdentifierExpression>());
+    ident = rel->rhs->As<ast::IdentifierExpression>();
+    EXPECT_EQ(ident->symbol, p->builder().Symbols().Get("c"));
+}
+
+TEST_F(ParserImplTest, MathExpression_NoMatch_ReturnLHS) {
+    auto p = parser("a if");
+    auto lhs = p->unary_expression();
+    auto e = p->expect_math_expression_post_unary_expression(lhs.value);
+    EXPECT_FALSE(e.errored);
+    EXPECT_FALSE(p->has_error()) << p->error();
+    ASSERT_NE(e.value, nullptr);
+    EXPECT_EQ(lhs.value, e.value);
+}
+
+TEST_F(ParserImplTest, MathExpression_InvalidRHS) {
+    auto p = parser("a * if");
+    auto lhs = p->unary_expression();
+    auto e = p->expect_math_expression_post_unary_expression(lhs.value);
+    EXPECT_TRUE(e.errored);
+    EXPECT_TRUE(p->has_error());
+    ASSERT_EQ(e.value, nullptr);
+    EXPECT_EQ("1:5: unable to parse right side of * expression", p->error());
+}
+
+}  // namespace
+}  // namespace tint::reader::wgsl

src/tint/reader/wgsl/parser_impl_multiplicative_expression_test.cc

@@ -17,7 +17,7 @@
 namespace tint::reader::wgsl {
 namespace {
 
-TEST_F(ParserImplTest, MultiplicativeExpression_Parses_Multiply) {
+TEST_F(ParserImplTest, MultiplicativeExpression_Orig_Parses_Multiply) {
     auto p = parser("a * true");
     auto e = p->multiplicative_expression();
     EXPECT_TRUE(e.matched);
@@ -42,7 +42,7 @@ TEST_F(ParserImplTest, MultiplicativeExpression_Parses_Multiply) {
     ASSERT_TRUE(rel->rhs->As<ast::BoolLiteralExpression>()->value);
 }
 
-TEST_F(ParserImplTest, MultiplicativeExpression_Parses_Divide) {
+TEST_F(ParserImplTest, MultiplicativeExpression_Orig_Parses_Divide) {
     auto p = parser("a / true");
     auto e = p->multiplicative_expression();
     EXPECT_TRUE(e.matched);
@@ -62,7 +62,7 @@ TEST_F(ParserImplTest, MultiplicativeExpression_Parses_Divide) {
     ASSERT_TRUE(rel->rhs->As<ast::BoolLiteralExpression>()->value);
 }
 
-TEST_F(ParserImplTest, MultiplicativeExpression_Parses_Modulo) {
+TEST_F(ParserImplTest, MultiplicativeExpression_Orig_Parses_Modulo) {
     auto p = parser("a % true");
     auto e = p->multiplicative_expression();
     EXPECT_TRUE(e.matched);
@@ -82,7 +82,7 @@ TEST_F(ParserImplTest, MultiplicativeExpression_Parses_Modulo) {
     ASSERT_TRUE(rel->rhs->As<ast::BoolLiteralExpression>()->value);
 }
 
-TEST_F(ParserImplTest, MultiplicativeExpression_InvalidLHS) {
+TEST_F(ParserImplTest, MultiplicativeExpression_Orig_InvalidLHS) {
     auto p = parser("if (a) {} * true");
     auto e = p->multiplicative_expression();
     EXPECT_FALSE(e.matched);
@@ -91,7 +91,7 @@ TEST_F(ParserImplTest, MultiplicativeExpression_InvalidLHS) {
     EXPECT_EQ(e.value, nullptr);
 }
 
-TEST_F(ParserImplTest, MultiplicativeExpression_InvalidRHS) {
+TEST_F(ParserImplTest, MultiplicativeExpression_Orig_InvalidRHS) {
     auto p = parser("true * if (a) {}");
     auto e = p->multiplicative_expression();
     EXPECT_FALSE(e.matched);
@@ -101,7 +101,7 @@ TEST_F(ParserImplTest, MultiplicativeExpression_InvalidRHS) {
     EXPECT_EQ(p->error(), "1:8: unable to parse right side of * expression");
 }
 
-TEST_F(ParserImplTest, MultiplicativeExpression_NoOr_ReturnsLHS) {
+TEST_F(ParserImplTest, MultiplicativeExpression_Orig_NoOr_ReturnsLHS) {
     auto p = parser("a true");
     auto e = p->multiplicative_expression();
     EXPECT_TRUE(e.matched);
@@ -111,5 +111,170 @@ TEST_F(ParserImplTest, MultiplicativeExpression_NoOr_ReturnsLHS) {
     ASSERT_TRUE(e->Is<ast::IdentifierExpression>());
 }
 
+TEST_F(ParserImplTest, MultiplicativeExpression_Parses_Multiply) {
+    auto p = parser("a * b");
+    auto lhs = p->unary_expression();
+    auto e = p->expect_multiplicative_expression_post_unary_expression(lhs.value);
+    EXPECT_FALSE(e.errored);
+    EXPECT_FALSE(p->has_error()) << p->error();
+    ASSERT_NE(e.value, nullptr);
+
+    ASSERT_TRUE(e->Is<ast::BinaryExpression>());
+    auto* rel = e->As<ast::BinaryExpression>();
+    EXPECT_EQ(ast::BinaryOp::kMultiply, rel->op);
+
+    ASSERT_TRUE(rel->lhs->Is<ast::IdentifierExpression>());
+    auto* ident = rel->lhs->As<ast::IdentifierExpression>();
+    EXPECT_EQ(ident->symbol, p->builder().Symbols().Get("a"));
+
+    ASSERT_TRUE(rel->rhs->Is<ast::IdentifierExpression>());
+    ident = rel->rhs->As<ast::IdentifierExpression>();
+    EXPECT_EQ(ident->symbol, p->builder().Symbols().Get("b"));
+}
+
+TEST_F(ParserImplTest, MultiplicativeExpression_Parses_Multiply_UnaryIndirect) {
+    auto p = parser("a **b");
+    auto lhs = p->unary_expression();
+    auto e = p->expect_multiplicative_expression_post_unary_expression(lhs.value);
+    EXPECT_FALSE(e.errored);
+    EXPECT_FALSE(p->has_error()) << p->error();
+    ASSERT_NE(e.value, nullptr);
+
+    ASSERT_TRUE(e->Is<ast::BinaryExpression>());
+    auto* rel = e->As<ast::BinaryExpression>();
+    EXPECT_EQ(ast::BinaryOp::kMultiply, rel->op);
+
+    ASSERT_TRUE(rel->lhs->Is<ast::IdentifierExpression>());
+    auto* ident = rel->lhs->As<ast::IdentifierExpression>();
+    EXPECT_EQ(ident->symbol, p->builder().Symbols().Get("a"));
+
+    ASSERT_TRUE(rel->rhs->Is<ast::UnaryOpExpression>());
+    auto* unary = rel->rhs->As<ast::UnaryOpExpression>();
+    EXPECT_EQ(ast::UnaryOp::kIndirection, unary->op);
+
+    ASSERT_TRUE(unary->expr->Is<ast::IdentifierExpression>());
+    ident = unary->expr->As<ast::IdentifierExpression>();
+    EXPECT_EQ(ident->symbol, p->builder().Symbols().Get("b"));
+}
+
+TEST_F(ParserImplTest, MultiplicativeExpression_Parses_Divide) {
+    auto p = parser("a / b");
+    auto lhs = p->unary_expression();
+    auto e = p->expect_multiplicative_expression_post_unary_expression(lhs.value);
+    EXPECT_FALSE(e.errored);
+    EXPECT_FALSE(p->has_error()) << p->error();
+    ASSERT_NE(e.value, nullptr);
+
+    ASSERT_TRUE(e->Is<ast::BinaryExpression>());
+    auto* rel = e->As<ast::BinaryExpression>();
+    EXPECT_EQ(ast::BinaryOp::kDivide, rel->op);
+
+    ASSERT_TRUE(rel->lhs->Is<ast::IdentifierExpression>());
+    auto* ident = rel->lhs->As<ast::IdentifierExpression>();
+    EXPECT_EQ(ident->symbol, p->builder().Symbols().Get("a"));
+
+    ASSERT_TRUE(rel->rhs->Is<ast::IdentifierExpression>());
+    ident = rel->rhs->As<ast::IdentifierExpression>();
+    EXPECT_EQ(ident->symbol, p->builder().Symbols().Get("b"));
+}
+
+TEST_F(ParserImplTest, MultiplicativeExpression_Parses_Modulo) {
+    auto p = parser("a % b");
+    auto lhs = p->unary_expression();
+    auto e = p->expect_multiplicative_expression_post_unary_expression(lhs.value);
+    EXPECT_FALSE(e.errored);
+    EXPECT_FALSE(p->has_error()) << p->error();
+    ASSERT_NE(e.value, nullptr);
+
+    ASSERT_TRUE(e->Is<ast::BinaryExpression>());
+    auto* rel = e->As<ast::BinaryExpression>();
+    EXPECT_EQ(ast::BinaryOp::kModulo, rel->op);
+
+    ASSERT_TRUE(rel->lhs->Is<ast::IdentifierExpression>());
+    auto* ident = rel->lhs->As<ast::IdentifierExpression>();
+    EXPECT_EQ(ident->symbol, p->builder().Symbols().Get("a"));
+
+    ASSERT_TRUE(rel->rhs->Is<ast::IdentifierExpression>());
+    ident = rel->rhs->As<ast::IdentifierExpression>();
+    EXPECT_EQ(ident->symbol, p->builder().Symbols().Get("b"));
+}
+
+TEST_F(ParserImplTest, MultiplicativeExpression_Parses_Grouping) {
+    auto p = parser("a * b / c % d * e");
+    auto lhs = p->unary_expression();
+    auto e = p->expect_multiplicative_expression_post_unary_expression(lhs.value);
+    EXPECT_FALSE(e.errored);
+    EXPECT_FALSE(p->has_error()) << p->error();
+    ASSERT_NE(e.value, nullptr);
+
+    ASSERT_TRUE(e->Is<ast::BinaryExpression>());
+    // lhs: ((a * b) / c) % d
+    // op: *
+    // rhs: e
+    auto* rel = e->As<ast::BinaryExpression>();
+    EXPECT_EQ(ast::BinaryOp::kMultiply, rel->op);
+
+    ASSERT_TRUE(rel->rhs->Is<ast::IdentifierExpression>());
+    auto* ident = rel->rhs->As<ast::IdentifierExpression>();
+    EXPECT_EQ(ident->symbol, p->builder().Symbols().Get("e"));
+
+    ASSERT_TRUE(rel->lhs->Is<ast::BinaryExpression>());
+    // lhs: (a * b) / c
+    // op: %
+    // rhs: d
+    rel = rel->lhs->As<ast::BinaryExpression>();
+    EXPECT_EQ(ast::BinaryOp::kModulo, rel->op);
+
+    ASSERT_TRUE(rel->rhs->Is<ast::IdentifierExpression>());
+    ident = rel->rhs->As<ast::IdentifierExpression>();
+    EXPECT_EQ(ident->symbol, p->builder().Symbols().Get("d"));
+
+    ASSERT_TRUE(rel->lhs->Is<ast::BinaryExpression>());
+    // lhs: a * b
+    // op: /
+    // rhs: c
+    rel = rel->lhs->As<ast::BinaryExpression>();
+    EXPECT_EQ(ast::BinaryOp::kDivide, rel->op);
+
+    ASSERT_TRUE(rel->rhs->Is<ast::IdentifierExpression>());
+    ident = rel->rhs->As<ast::IdentifierExpression>();
+    EXPECT_EQ(ident->symbol, p->builder().Symbols().Get("c"));
+
+    ASSERT_TRUE(rel->lhs->Is<ast::BinaryExpression>());
+    // lhs: a
+    // op: *
+    // rhs: b
+    rel = rel->lhs->As<ast::BinaryExpression>();
+    EXPECT_EQ(ast::BinaryOp::kMultiply, rel->op);
+
+    ASSERT_TRUE(rel->lhs->Is<ast::IdentifierExpression>());
+    ident = rel->lhs->As<ast::IdentifierExpression>();
+    EXPECT_EQ(ident->symbol, p->builder().Symbols().Get("a"));
+
+    ASSERT_TRUE(rel->rhs->Is<ast::IdentifierExpression>());
+    ident = rel->rhs->As<ast::IdentifierExpression>();
+    EXPECT_EQ(ident->symbol, p->builder().Symbols().Get("b"));
+}
+
+TEST_F(ParserImplTest, MultiplicativeExpression_InvalidRHS) {
+    auto p = parser("a * if (a) {}");
+    auto lhs = p->unary_expression();
+    auto e = p->expect_multiplicative_expression_post_unary_expression(lhs.value);
+    EXPECT_TRUE(e.errored);
+    EXPECT_EQ(e.value, nullptr);
+    ASSERT_TRUE(p->has_error());
+    EXPECT_EQ(p->error(), "1:5: unable to parse right side of * expression");
+}
+
+TEST_F(ParserImplTest, MultiplicativeExpression_NoMatch_ReturnsLHS) {
+    auto p = parser("a + b");
+    auto lhs = p->unary_expression();
+    auto e = p->expect_multiplicative_expression_post_unary_expression(lhs.value);
+    EXPECT_FALSE(e.errored);
+    EXPECT_FALSE(p->has_error()) << p->error();
+    ASSERT_NE(e.value, nullptr);
+    EXPECT_EQ(lhs.value, e.value);
+}
+
 }  // namespace
 }  // namespace tint::reader::wgsl

src/tint/reader/wgsl/parser_impl_type_decl_test.cc

@@ -469,6 +469,33 @@ TEST_F(ParserImplTest, TypeDecl_Array_ConstantSize) {
     EXPECT_EQ(p->builder().Symbols().NameFor(count_expr->symbol), "size");
 }
 
+TEST_F(ParserImplTest, TypeDecl_Array_ExpressionSize) {
+    auto p = parser("array<f32, size + 2>");
+    auto t = p->type_decl();
+    EXPECT_TRUE(t.matched);
+    EXPECT_FALSE(t.errored);
+    ASSERT_NE(t.value, nullptr) << p->error();
+    ASSERT_FALSE(p->has_error());
+    ASSERT_TRUE(t.value->Is<ast::Array>());
+
+    auto* a = t.value->As<ast::Array>();
+    ASSERT_FALSE(a->IsRuntimeArray());
+    ASSERT_TRUE(a->type->Is<ast::F32>());
+    EXPECT_EQ(a->attributes.Length(), 0u);
+
+    ASSERT_TRUE(a->count->Is<ast::BinaryExpression>());
+    auto* count_expr = a->count->As<ast::BinaryExpression>();
+    EXPECT_EQ(ast::BinaryOp::kAdd, count_expr->op);
+
+    ASSERT_TRUE(count_expr->lhs->Is<ast::IdentifierExpression>());
+    auto* ident = count_expr->lhs->As<ast::IdentifierExpression>();
+    EXPECT_EQ(p->builder().Symbols().NameFor(ident->symbol), "size");
+
+    ASSERT_TRUE(count_expr->rhs->Is<ast::IntLiteralExpression>());
+    auto* val = count_expr->rhs->As<ast::IntLiteralExpression>();
+    EXPECT_EQ(2, static_cast<int32_t>(val->value));
+}
+
 TEST_F(ParserImplTest, TypeDecl_Array_Runtime) {
     auto p = parser("array<u32>");
     auto t = p->type_decl();
@@ -524,7 +551,7 @@ TEST_F(ParserImplTest, TypeDecl_Array_BadSize) {
     EXPECT_FALSE(t.matched);
     ASSERT_EQ(t.value, nullptr);
     ASSERT_TRUE(p->has_error());
-    ASSERT_EQ(p->error(), "1:12: expected array size expression");
+    ASSERT_EQ(p->error(), "1:13: unable to parse right side of ! expression");
 }
 
 TEST_F(ParserImplTest, TypeDecl_Array_MissingSize) {

src/tint/reader/wgsl/token.h

@@ -380,7 +380,7 @@ class Token {
     /// @returns true if the token can be split during parse into component tokens
     bool IsSplittable() const {
         return Is(Token::Type::kShiftRight) || Is(Token::Type::kGreaterThanEqual) ||
-               Is(Token::Type::kAndAnd);
+               Is(Token::Type::kAndAnd) || Is(Token::Type::kMinusMinus);
     }
 
     /// @returns the source information for this token