Emit Return statements.

This CL adds emitting return statements into the WGSL writer.

Bug: tint:4
Change-Id: Ia2331f7c20e3a3e3af1aa1553cef83bec315eae3
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/17260
Reviewed-by: David Neto <dneto@google.com>

src/CMakeLists.txt

@@ -422,6 +422,7 @@ if(${TINT_BUILD_WGSL_WRITER})
     writer/wgsl/generator_impl_member_accessor_test.cc
     writer/wgsl/generator_impl_nop_test.cc
     writer/wgsl/generator_impl_relational_test.cc
+    writer/wgsl/generator_impl_return_test.cc
     writer/wgsl/generator_impl_type_test.cc
     writer/wgsl/generator_impl_unary_derivative_test.cc
     writer/wgsl/generator_impl_unary_method_test.cc

src/ast/return_statement.h

@@ -50,6 +50,8 @@ class ReturnStatement : public Statement {
   }
   /// @returns the value
   Expression* value() const { return value_.get(); }
+  /// @returns true if the return has a value
+  bool has_value() const { return value_ != nullptr; }
 
   /// @returns true if this is a return statement
   bool IsReturn() const override { return true; }

src/ast/return_statement_test.cc

@@ -44,6 +44,17 @@ TEST_F(ReturnStatementTest, IsReturn) {
   EXPECT_TRUE(r.IsReturn());
 }
 
+TEST_F(ReturnStatementTest, HasValue_WithoutValue) {
+  ReturnStatement r;
+  EXPECT_FALSE(r.has_value());
+}
+
+TEST_F(ReturnStatementTest, HasValue_WithValue) {
+  auto expr = std::make_unique<IdentifierExpression>("expr");
+  ReturnStatement r(std::move(expr));
+  EXPECT_TRUE(r.has_value());
+}
+
 TEST_F(ReturnStatementTest, IsValid_WithoutValue) {
   ReturnStatement r;
   EXPECT_TRUE(r.IsValid());

src/writer/wgsl/generator_impl.cc

@@ -37,6 +37,7 @@
 #include "src/ast/location_decoration.h"
 #include "src/ast/member_accessor_expression.h"
 #include "src/ast/relational_expression.h"
+#include "src/ast/return_statement.h"
 #include "src/ast/set_decoration.h"
 #include "src/ast/statement.h"
 #include "src/ast/struct.h"
@@ -669,6 +670,9 @@ bool GeneratorImpl::EmitStatement(ast::Statement* stmt) {
   if (stmt->IsNop()) {
     return EmitNop(stmt->AsNop());
   }
+  if (stmt->IsReturn()) {
+    return EmitReturn(stmt->AsReturn());
+  }
 
   error_ = "unknown statement type";
   return false;
@@ -789,6 +793,20 @@ bool GeneratorImpl::EmitNop(ast::NopStatement*) {
   return true;
 }
 
+bool GeneratorImpl::EmitReturn(ast::ReturnStatement* stmt) {
+  make_indent();
+
+  out_ << "return";
+  if (stmt->has_value()) {
+    out_ << " ";
+    if (!EmitExpression(stmt->value())) {
+      return false;
+    }
+  }
+  out_ << ";" << std::endl;
+  return true;
+}
+
 }  // namespace wgsl
 }  // namespace writer
 }  // namespace tint

src/writer/wgsl/generator_impl.h

@@ -150,6 +150,10 @@ class GeneratorImpl {
   /// @param expr the relational expression
   /// @returns true if the expression was emitted, false otherwise
   bool EmitRelational(ast::RelationalExpression* expr);
+  /// Handles return statements
+  /// @param stmt the statement to emit
+  /// @returns true if the statement was successfully emitted
+  bool EmitReturn(ast::ReturnStatement* stmt);
   /// Handles statements
   /// @param stmt the statement to emit
   /// @returns true if the statement was emitted

src/writer/wgsl/generator_impl_return_test.cc

@@ -0,0 +1,54 @@
+// 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 <vector>
+
+#include "gtest/gtest.h"
+#include "src/ast/identifier_expression.h"
+#include "src/ast/return_statement.h"
+#include "src/writer/wgsl/generator_impl.h"
+
+namespace tint {
+namespace writer {
+namespace wgsl {
+namespace {
+
+using GeneratorImplTest = testing::Test;
+
+TEST_F(GeneratorImplTest, Emit_Return) {
+  ast::ReturnStatement r;
+
+  GeneratorImpl g;
+  g.increment_indent();
+
+  ASSERT_TRUE(g.EmitStatement(&r)) << g.error();
+  EXPECT_EQ(g.result(), "  return;\n");
+}
+
+TEST_F(GeneratorImplTest, Emit_ReturnWithValue) {
+  auto expr = std::make_unique<ast::IdentifierExpression>("expr");
+  ast::ReturnStatement r(std::move(expr));
+
+  GeneratorImpl g;
+  g.increment_indent();
+
+  ASSERT_TRUE(g.EmitStatement(&r)) << g.error();
+  EXPECT_EQ(g.result(), "  return expr;\n");
+}
+
+}  // namespace
+}  // namespace wgsl
+}  // namespace writer
+}  // namespace tint