Emit Unless statement.

This CL adds unless statement to the WGSL generator.

Bug: tint:4
Change-Id: Id171cb1438d290938f1da946c23992bdae688359
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/17280
Reviewed-by: David Neto <dneto@google.com>

src/CMakeLists.txt

@@ -428,6 +428,7 @@ if(${TINT_BUILD_WGSL_WRITER})
     writer/wgsl/generator_impl_unary_derivative_test.cc
     writer/wgsl/generator_impl_unary_method_test.cc
     writer/wgsl/generator_impl_unary_op_test.cc
+    writer/wgsl/generator_impl_unless_test.cc
     writer/wgsl/generator_impl_variable_test.cc
   )
 endif()

src/writer/wgsl/generator_impl.cc

@@ -39,6 +39,7 @@
 #include "src/ast/regardless_statement.h"
 #include "src/ast/relational_expression.h"
 #include "src/ast/return_statement.h"
+#include "src/ast/unless_statement.h"
 #include "src/ast/set_decoration.h"
 #include "src/ast/statement.h"
 #include "src/ast/struct.h"
@@ -677,6 +678,9 @@ bool GeneratorImpl::EmitStatement(ast::Statement* stmt) {
   if (stmt->IsReturn()) {
     return EmitReturn(stmt->AsReturn());
   }
+  if (stmt->IsUnless()) {
+    return EmitUnless(stmt->AsUnless());
+  }
 
   error_ = "unknown statement type";
   return false;
@@ -832,6 +836,27 @@ bool GeneratorImpl::EmitReturn(ast::ReturnStatement* stmt) {
   return true;
 }
 
+bool GeneratorImpl::EmitUnless(ast::UnlessStatement* stmt) {
+  make_indent();
+
+  out_ << "unless (";
+  if (!EmitExpression(stmt->condition())) {
+    return false;
+  }
+  out_ << ") {" << std::endl;
+
+  increment_indent();
+  for (const auto& b : stmt->body()) {
+    if (!EmitStatement(b.get())) {
+      return false;
+    }
+  }
+  decrement_indent();
+  make_indent();
+  out_ << "}" << std::endl;
+  return true;
+}
+
 }  // namespace wgsl
 }  // namespace writer
 }  // namespace tint

src/writer/wgsl/generator_impl.h

@@ -182,6 +182,10 @@ class GeneratorImpl {
   /// @param expr the expression to emit
   /// @returns true if the expression was emitted
   bool EmitUnaryOp(ast::UnaryOpExpression* expr);
+  /// Handles generating an unless statement
+  /// @param stmt the statement to generate
+  /// @returns true if the statement was successfully emitted
+  bool EmitUnless(ast::UnlessStatement* stmt);
   /// Handles generating a variable
   /// @param var the variable to generate
   /// @returns true if the variable was emitted

src/writer/wgsl/generator_impl_unless_test.cc

@@ -0,0 +1,56 @@
+// 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/kill_statement.h"
+#include "src/ast/nop_statement.h"
+#include "src/ast/unless_statement.h"
+#include "src/writer/wgsl/generator_impl.h"
+
+namespace tint {
+namespace writer {
+namespace wgsl {
+namespace {
+
+using GeneratorImplTest = testing::Test;
+
+TEST_F(GeneratorImplTest, Emit_Unless) {
+  auto cond = std::make_unique<ast::IdentifierExpression>("cond");
+
+  std::vector<std::unique_ptr<ast::Statement>> body;
+  body.push_back(std::make_unique<ast::NopStatement>());
+  body.push_back(std::make_unique<ast::KillStatement>());
+
+  ast::UnlessStatement u(std::move(cond), std::move(body));
+
+  GeneratorImpl g;
+  g.increment_indent();
+
+  ASSERT_TRUE(g.EmitStatement(&u)) << g.error();
+  EXPECT_EQ(g.result(), R"(  unless (cond) {
+    nop;
+    kill;
+  }
+)");
+}
+
+}  // namespace
+}  // namespace wgsl
+}  // namespace writer
+}  // namespace tint
+