Emit Cast expression.

This CL adds Cast Expression emission to the WGSL generator.

Bug: tint:4
Change-Id: Ib48290d53423be5770cfb8f1b5f1ccb93b53a4df
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/17062
Reviewed-by: David Neto <dneto@google.com>

src/CMakeLists.txt

@@ -408,6 +408,7 @@ if(${TINT_BUILD_WGSL_WRITER})
     writer/wgsl/generator_impl_array_accessor_test.cc
     writer/wgsl/generator_impl_as_test.cc
     writer/wgsl/generator_impl_call_test.cc
+    writer/wgsl/generator_impl_cast_test.cc
     writer/wgsl/generator_impl_entry_point_test.cc
     writer/wgsl/generator_impl_identifier_test.cc
     writer/wgsl/generator_impl_import_test.cc

src/writer/wgsl/generator_impl.cc

@@ -23,6 +23,7 @@
 #include "src/ast/bool_literal.h"
 #include "src/ast/builtin_decoration.h"
 #include "src/ast/call_expression.h"
+#include "src/ast/cast_expression.h"
 #include "src/ast/const_initializer_expression.h"
 #include "src/ast/decorated_variable.h"
 #include "src/ast/float_literal.h"
@@ -126,6 +127,9 @@ bool GeneratorImpl::EmitExpression(ast::Expression* expr) {
   if (expr->IsCall()) {
     return EmitCall(expr->AsCall());
   }
+  if (expr->IsCast()) {
+    return EmitCast(expr->AsCast());
+  }
   if (expr->IsIdentifier()) {
     return EmitIdentifier(expr->AsIdentifier());
   }
@@ -190,6 +194,21 @@ bool GeneratorImpl::EmitCall(ast::CallExpression* expr) {
   return true;
 }
 
+bool GeneratorImpl::EmitCast(ast::CastExpression* expr) {
+  out_ << "cast<";
+  if (!EmitType(expr->type())) {
+    return false;
+  }
+
+  out_ << ">(";
+  if (!EmitExpression(expr->expr())) {
+    return false;
+  }
+
+  out_ << ")";
+  return true;
+}
+
 bool GeneratorImpl::EmitInitializer(ast::InitializerExpression* expr) {
   if (expr->IsConstInitializer()) {
     return EmitConstInitializer(expr->AsConstInitializer());

src/writer/wgsl/generator_impl.h

@@ -82,6 +82,10 @@ class GeneratorImpl {
   /// @param expr the call expression
   /// @returns true if the call expression is emitted
   bool EmitCall(ast::CallExpression* expr);
+  /// Handles generating a cast expression
+  /// @param expr the cast expression
+  /// @returns true if the cast was emitted
+  bool EmitCast(ast::CastExpression* expr);
   /// Handles generating a const initializer
   /// @param expr the const initializer expression
   /// @returns true if the initializer is emitted

src/writer/wgsl/generator_impl_cast_test.cc

@@ -0,0 +1,43 @@
+// Copyright 2020 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 <memory>
+
+#include "gtest/gtest.h"
+#include "src/ast/cast_expression.h"
+#include "src/ast/identifier_expression.h"
+#include "src/ast/type/f32_type.h"
+#include "src/writer/wgsl/generator_impl.h"
+
+namespace tint {
+namespace writer {
+namespace wgsl {
+namespace {
+
+using GeneratorImplTest = testing::Test;
+
+TEST_F(GeneratorImplTest, EmitExpression_Cast) {
+  ast::type::F32Type f32;
+  auto id = std::make_unique<ast::IdentifierExpression>("id");
+  ast::CastExpression cast(&f32, std::move(id));
+
+  GeneratorImpl g;
+  ASSERT_TRUE(g.EmitExpression(&cast)) << g.error();
+  EXPECT_EQ(g.result(), "cast<f32>(id)");
+}
+
+}  // namespace
+}  // namespace wgsl
+}  // namespace writer
+}  // namespace tint