[metal-writer] Add return generation.

This CL adds generation of the return statement.

Bug: tint:8
Change-Id: Iffee600e77a485649b987d39aab47742968e438e
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/23702
Reviewed-by: David Neto <dneto@google.com>

BUILD.gn

@@ -885,6 +885,7 @@ source_set("tint_unittests_wgsl_writer_src") {
 
 source_set("tint_unittests_msl_writer_src") {
   sources = [
+    "src/writer/msl/generator_impl_return_test.cc",
     "src/writer/msl/generator_impl_test.cc",
     "src/writer/msl/generator_impl_type_test.cc",
   ]

src/CMakeLists.txt

@@ -493,6 +493,7 @@ endif()
 
 if(${TINT_BUILD_MSL_WRITER})
   list(APPEND TINT_TEST_SRCS
+    writer/msl/generator_impl_return_test.cc
     writer/msl/generator_impl_test.cc
     writer/msl/generator_impl_type_test.cc
   )

src/writer/msl/generator_impl.cc

@@ -14,6 +14,7 @@
 
 #include "src/writer/msl/generator_impl.h"
 
+#include "src/ast/return_statement.h"
 #include "src/ast/type/alias_type.h"
 #include "src/ast/type/array_type.h"
 #include "src/ast/type/bool_type.h"
@@ -38,6 +39,61 @@ bool GeneratorImpl::Generate(const ast::Module&) {
   return true;
 }
 
+bool GeneratorImpl::EmitExpression(ast::Expression*) {
+  error_ = "unknown expression type";
+  return false;
+}
+
+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;
+}
+
+bool GeneratorImpl::EmitStatementBlock(const ast::StatementList& statements) {
+  out_ << " {" << std::endl;
+
+  increment_indent();
+
+  for (const auto& s : statements) {
+    if (!EmitStatement(s.get())) {
+      return false;
+    }
+  }
+
+  decrement_indent();
+  make_indent();
+  out_ << "}";
+
+  return true;
+}
+
+bool GeneratorImpl::EmitStatementBlockAndNewline(
+    const ast::StatementList& statements) {
+  const bool result = EmitStatementBlock(statements);
+  if (result) {
+    out_ << std::endl;
+  }
+  return result;
+}
+
+bool GeneratorImpl::EmitStatement(ast::Statement* stmt) {
+  if (stmt->IsReturn()) {
+    return EmitReturn(stmt->AsReturn());
+  }
+
+  error_ = "unknown statement type";
+  return false;
+}
+
 bool GeneratorImpl::EmitType(ast::type::Type* type, const std::string& name) {
   if (type->IsAlias()) {
     auto* alias = type->AsAlias();

src/writer/msl/generator_impl.h

@@ -37,6 +37,26 @@ class GeneratorImpl : public TextGenerator {
   /// @returns true on successful generation; false otherwise
   bool Generate(const ast::Module& module);
 
+  /// Handles generate an Expression
+  /// @param expr the expression
+  /// @returns true if the expression was emitted
+  bool EmitExpression(ast::Expression* expr);
+  /// Handles return statements
+  /// @param stmt the statement to emit
+  /// @returns true if the statement was successfully emitted
+  bool EmitReturn(ast::ReturnStatement* stmt);
+  /// Handles a brace-enclosed list of statements.
+  /// @param statements the statements to output
+  /// @returns true if the statements were emitted
+  bool EmitStatementBlock(const ast::StatementList& statements);
+  /// Handles a brace-enclosed list of statements and trailing newline.
+  /// @param statements the statements to output
+  /// @returns true if the statements were emitted
+  bool EmitStatementBlockAndNewline(const ast::StatementList& statements);
+  /// Handles statement
+  /// @param stmt the statement to emit
+  /// @returns true if the statement was emitted
+  bool EmitStatement(ast::Statement* stmt);
   /// Handles generating type
   /// @param type the type to generate
   /// @param name the name of the variable, only used for array emission

src/writer/msl/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/msl/generator_impl.h"
+
+namespace tint {
+namespace writer {
+namespace msl {
+namespace {
+
+using MslGeneratorImplTest = testing::Test;
+
+TEST_F(MslGeneratorImplTest, 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(MslGeneratorImplTest, DISABLED_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 msl
+}  // namespace writer
+}  // namespace tint