Emit switch statements.

This CL updates the WGSL generator to output switch statements.

Bug: tint:4
Change-Id: I4450b10932960691c76e76869105ade01fdd5a79
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/17282
Reviewed-by: David Neto <dneto@google.com>

src/CMakeLists.txt

@@ -424,6 +424,7 @@ if(${TINT_BUILD_WGSL_WRITER})
     writer/wgsl/generator_impl_regardless_test.cc
     writer/wgsl/generator_impl_relational_test.cc
     writer/wgsl/generator_impl_return_test.cc
+    writer/wgsl/generator_impl_switch_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/writer/wgsl/generator_impl.cc

@@ -44,6 +44,7 @@
 #include "src/ast/struct.h"
 #include "src/ast/struct_member.h"
 #include "src/ast/struct_member_offset_decoration.h"
+#include "src/ast/switch_statement.h"
 #include "src/ast/type/array_type.h"
 #include "src/ast/type/matrix_type.h"
 #include "src/ast/type/pointer_type.h"
@@ -679,6 +680,9 @@ bool GeneratorImpl::EmitStatement(ast::Statement* stmt) {
   if (stmt->IsReturn()) {
     return EmitReturn(stmt->AsReturn());
   }
+  if (stmt->IsSwitch()) {
+    return EmitSwitch(stmt->AsSwitch());
+  }
   if (stmt->IsVariable()) {
     return EmitVariable(stmt->AsVariable()->variable());
   }
@@ -840,6 +844,30 @@ bool GeneratorImpl::EmitReturn(ast::ReturnStatement* stmt) {
   return true;
 }
 
+bool GeneratorImpl::EmitSwitch(ast::SwitchStatement* stmt) {
+  make_indent();
+
+  out_ << "switch(";
+  if (!EmitExpression(stmt->condition())) {
+    return false;
+  }
+  out_ << ") {" << std::endl;
+
+  increment_indent();
+
+  for (const auto& s : stmt->body()) {
+    if (!EmitCase(s.get())) {
+      return false;
+    }
+  }
+
+  decrement_indent();
+  make_indent();
+  out_ << "}" << std::endl;
+
+  return true;
+}
+
 bool GeneratorImpl::EmitUnless(ast::UnlessStatement* stmt) {
   make_indent();
 

src/writer/wgsl/generator_impl.h

@@ -162,6 +162,10 @@ class GeneratorImpl {
   /// @param stmt the statement to emit
   /// @returns true if the statement was emitted
   bool EmitStatement(ast::Statement* stmt);
+  /// Handles generating a switch statement
+  /// @param stmt the statement to emit
+  /// @returns true if the statement was emitted
+  bool EmitSwitch(ast::SwitchStatement* stmt);
   /// Handles generating type
   /// @param type the type to generate
   /// @returns true if the type is emitted

src/writer/wgsl/generator_impl_switch_test.cc

@@ -0,0 +1,71 @@
+// 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/break_statement.h"
+#include "src/ast/case_statement.h"
+#include "src/ast/identifier_expression.h"
+#include "src/ast/int_literal.h"
+#include "src/ast/switch_statement.h"
+#include "src/writer/wgsl/generator_impl.h"
+
+namespace tint {
+namespace writer {
+namespace wgsl {
+namespace {
+
+using GeneratorImplTest = testing::Test;
+
+TEST_F(GeneratorImplTest, Emit_Switch) {
+  auto def = std::make_unique<ast::CaseStatement>();
+  std::vector<std::unique_ptr<ast::Statement>> def_body;
+  def_body.push_back(std::make_unique<ast::BreakStatement>());
+  def->set_body(std::move(def_body));
+
+  auto case_val = std::make_unique<ast::IntLiteral>(5);
+  std::vector<std::unique_ptr<ast::Statement>> case_body;
+  case_body.push_back(std::make_unique<ast::BreakStatement>());
+
+  auto case_stmt = std::make_unique<ast::CaseStatement>(std::move(case_val),
+                                                        std::move(case_body));
+
+  std::vector<std::unique_ptr<ast::CaseStatement>> body;
+  body.push_back(std::move(case_stmt));
+  body.push_back(std::move(def));
+
+  auto cond = std::make_unique<ast::IdentifierExpression>("cond");
+  ast::SwitchStatement s(std::move(cond), std::move(body));
+
+  GeneratorImpl g;
+  g.increment_indent();
+
+  ASSERT_TRUE(g.EmitStatement(&s)) << g.error();
+  EXPECT_EQ(g.result(), R"(  switch(cond) {
+    case 5: {
+      break;
+    }
+    default: {
+      break;
+    }
+  }
+)");
+}
+
+}  // namespace
+}  // namespace wgsl
+}  // namespace writer
+}  // namespace tint