[hlsl-writer] Add assignment statement.

This CL adds the assign statement emission to the HLSL backend.

Bug: tint:7
Change-Id: I3e46ac09170ea1af7444ae89267a82e1d1c42c52
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/25224
Reviewed-by: David Neto <dneto@google.com>

BUILD.gn

@@ -1018,6 +1018,7 @@ source_set("tint_unittests_msl_writer_src") {
 
 source_set("tint_unittests_hlsl_writer_src") {
   sources = [
+    "src/writer/hlsl/generator_impl_assign_test.cc",
     "src/writer/hlsl/generator_impl_binary_test.cc",
     "src/writer/hlsl/generator_impl_break_test.cc",
     "src/writer/hlsl/generator_impl_case_test.cc",

src/CMakeLists.txt

@@ -542,6 +542,7 @@ endif()
 
 if (${TINT_BUILD_HLSL_WRITER})
   list(APPEND TINT_TEST_SRCS
+    writer/hlsl/generator_impl_assign_test.cc
     writer/hlsl/generator_impl_binary_test.cc
     writer/hlsl/generator_impl_break_test.cc
     writer/hlsl/generator_impl_case_test.cc

src/writer/hlsl/generator_impl.cc

@@ -14,6 +14,7 @@
 
 #include "src/writer/hlsl/generator_impl.h"
 
+#include "src/ast/assignment_statement.h"
 #include "src/ast/binary_expression.h"
 #include "src/ast/bool_literal.h"
 #include "src/ast/case_statement.h"
@@ -72,6 +73,24 @@ std::string GeneratorImpl::current_ep_var_name(VarType type) {
   return name;
 }
 
+bool GeneratorImpl::EmitAssign(ast::AssignmentStatement* stmt) {
+  make_indent();
+
+  if (!EmitExpression(stmt->lhs())) {
+    return false;
+  }
+
+  out_ << " = ";
+
+  if (!EmitExpression(stmt->rhs())) {
+    return false;
+  }
+
+  out_ << ";" << std::endl;
+
+  return true;
+}
+
 bool GeneratorImpl::EmitBinary(ast::BinaryExpression* expr) {
   out_ << "(";
 
@@ -304,6 +323,9 @@ bool GeneratorImpl::EmitReturn(ast::ReturnStatement* stmt) {
 }
 
 bool GeneratorImpl::EmitStatement(ast::Statement* stmt) {
+  if (stmt->IsAssign()) {
+    return EmitAssign(stmt->AsAssign());
+  }
   if (stmt->IsBreak()) {
     return EmitBreak(stmt->AsBreak());
   }

src/writer/hlsl/generator_impl.h

@@ -36,6 +36,10 @@ class GeneratorImpl : public TextGenerator {
   /// @returns true on successful generation; false otherwise
   bool Generate();
 
+  /// Handles an assignment statement
+  /// @param stmt the statement to emit
+  /// @returns true if the statement was emitted successfully
+  bool EmitAssign(ast::AssignmentStatement* stmt);
   /// Handles generating a binary expression
   /// @param expr the binary expression
   /// @returns true if the expression was emitted, false otherwise

src/writer/hlsl/generator_impl_assign_test.cc

@@ -0,0 +1,47 @@
+// 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/assignment_statement.h"
+#include "src/ast/identifier_expression.h"
+#include "src/ast/module.h"
+#include "src/writer/hlsl/generator_impl.h"
+
+namespace tint {
+namespace writer {
+namespace hlsl {
+namespace {
+
+using HlslGeneratorImplTest = testing::Test;
+
+TEST_F(HlslGeneratorImplTest, Emit_Assign) {
+  auto lhs = std::make_unique<ast::IdentifierExpression>("lhs");
+  auto rhs = std::make_unique<ast::IdentifierExpression>("rhs");
+  ast::AssignmentStatement assign(std::move(lhs), std::move(rhs));
+
+  ast::Module m;
+  GeneratorImpl g(&m);
+  g.increment_indent();
+
+  ASSERT_TRUE(g.EmitStatement(&assign)) << g.error();
+  EXPECT_EQ(g.result(), "  lhs = rhs;\n");
+}
+
+}  // namespace
+}  // namespace hlsl
+}  // namespace writer
+}  // namespace tint