[destructuring] Implement initializers in patterns.

src/pattern-rewriter.cc

Index: src/pattern-rewriter.cc
diff --git a/src/pattern-rewriter.cc b/src/pattern-rewriter.cc
index 9f24a395a25c4a24d1a17a9e7f75eb0b97bef1ee..a97c009708cdd1ffbb793654a1b5838339cf3e8c 100644
--- a/src/pattern-rewriter.cc
+++ b/src/pattern-rewriter.cc
@@ -208,17 +208,22 @@ void Parser::PatternRewriter::VisitVariableProxy(VariableProxy* pattern) {
 }
 
 
-void Parser::PatternRewriter::VisitObjectLiteral(ObjectLiteral* pattern) {
-  auto temp = TemporaryDeclarationScope()->NewTemporary(
-      ast_value_factory()->empty_string());
+Variable* Parser::PatternRewriter::CreateTempVar(Expression* value) {
+  auto temp_scope = descriptor_->parser->scope_->DeclarationScope();
+  auto temp = temp_scope->NewTemporary(ast_value_factory()->empty_string());
   auto assignment =
       factory()->NewAssignment(Token::ASSIGN, factory()->NewVariableProxy(temp),
-                               current_value_, RelocInfo::kNoPosition);
+                               value, RelocInfo::kNoPosition);
 
   block_->AddStatement(
       factory()->NewExpressionStatement(assignment, RelocInfo::kNoPosition),
       zone());
+  return temp;
+}
+
 
+void Parser::PatternRewriter::VisitObjectLiteral(ObjectLiteral* pattern) {
+  auto temp = CreateTempVar(current_value_);
   if (pattern->properties()->length() == 0) {
     block_->AddStatement(descriptor_->parser->BuildAssertIsCoercible(temp),
                          zone());
@@ -240,7 +245,20 @@ void Parser::PatternRewriter::VisitArrayLiteral(ArrayLiteral* node) {
 
 
 void Parser::PatternRewriter::VisitAssignment(Assignment* node) {
-  // TODO(dslomov): implement.
+  // let {<pattern> = <init>} = <value>
+  //   becomes
+  // temp = <value>;
+  // <pattern> = temp === undefined ? <init> : temp;
+  DCHECK(node->op() == Token::ASSIGN);
+  auto temp = CreateTempVar(current_value_);
+  Expression* is_undefined = factory()->NewCompareOperation(
+      Token::EQ_STRICT, factory()->NewVariableProxy(temp),
+      factory()->NewUndefinedLiteral(RelocInfo::kNoPosition),
+      RelocInfo::kNoPosition);
+  Expression* value = factory()->NewConditional(
+      is_undefined, node->value(), factory()->NewVariableProxy(temp),
+      RelocInfo::kNoPosition);
+  RecurseIntoSubpattern(node->target(), value);
 }