[es6] implement destructuring assignment

src/parser.h

Index: src/parser.h
diff --git a/src/parser.h b/src/parser.h
index 8ff7b176f47f34dd7f7e8eb822d9dcd817388884..3893c2dc35d07e55606eab6d4d190d0bfc9d627c 100644
--- a/src/parser.h
+++ b/src/parser.h
@@ -876,6 +876,14 @@ class ParserTraits {
                                       ZoneList<v8::internal::Expression*>* args,
                                       int pos);
 
+  // Rewrite all DestructuringAssignments in the current FunctionState.
+  V8_INLINE void RewriteDestructuringAssignments();
+
+  V8_INLINE Expression* RewriteDestructuringAssignmentExpression(
+      Expression* expression);
+
+  V8_INLINE void ShouldRewriteDestructuringAssignment(Expression* assignment);
+
  private:
   Parser* parser_;
 };
@@ -1024,6 +1032,10 @@ class Parser : public ParserBase<ParserTraits> {
         const DeclarationParsingResult::Declaration* declaration,
         ZoneList<const AstRawString*>* names, bool* ok);
 
+    static void RewriteDestructuringAssignment(Parser* parser,
+                                               Assignment* assignment,
+                                               Scope* Scope, bool* ok);
+
     void set_initializer_position(int pos) { initializer_position_ = pos; }
 
    private:
@@ -1035,6 +1047,11 @@ class Parser : public ParserBase<ParserTraits> {
 #undef DECLARE_VISIT
     void Visit(AstNode* node) override;
 
+    enum PatternContext { BINDING, INITIALIZER, ASSIGNMENT };
+
+    PatternContext context() const { return context_; }
+    void set_context(PatternContext context) { context_ = context; }
+
     void RecurseIntoSubpattern(AstNode* pattern, Expression* value) {
       Expression* old_value = current_value_;
       current_value_ = value;
@@ -1042,14 +1059,21 @@ class Parser : public ParserBase<ParserTraits> {
       current_value_ = old_value;
     }
 
+    void VisitObjectLiteral(ObjectLiteral* node, Variable** temp_var);
+    void VisitArrayLiteral(ArrayLiteral* node, Variable** temp_var);
+
     Variable* CreateTempVar(Expression* value = nullptr);
 
-    AstNodeFactory* factory() const { return descriptor_->parser->factory(); }
+    AstNodeFactory* factory() const { return parser_->factory(); }
     AstValueFactory* ast_value_factory() const {
-      return descriptor_->parser->ast_value_factory();
+      return parser_->ast_value_factory();
     }
-    Zone* zone() const { return descriptor_->parser->zone(); }
+    Zone* zone() const { return parser_->zone(); }
+    Scope* scope() const { return scope_; }
 
+    Scope* scope_;
+    Parser* parser_;
+    PatternContext context_;
     Expression* pattern_;
     int initializer_position_;
     Block* block_;
@@ -1199,6 +1223,13 @@ class Parser : public ParserBase<ParserTraits> {
   void SetLanguageMode(Scope* scope, LanguageMode mode);
   void RaiseLanguageMode(LanguageMode mode);
 
+  V8_INLINE void RewriteDestructuringAssignments();
+
+  friend class InitializerRewriter;
+  void RewriteParameterInitializer(Expression* expr, Scope* scope);
+
+  Expression* RewriteDestructuringAssignmentExpression(Expression* expression);
+
   Scanner scanner_;
   PreParser* reusable_preparser_;
   Scope* original_scope_;  // for ES5 function declarations in sloppy eval
@@ -1387,6 +1418,55 @@ DoExpression* ParserTraits::ParseDoExpression(bool* ok) {
 }
 
 
+void ParserTraits::RewriteDestructuringAssignments() {
+  parser_->RewriteDestructuringAssignments();
+}
+
+
+void Parser::RewriteDestructuringAssignments() {
+  FunctionState* func = function_state_;
+  typedef typename ParserBase<ParserTraits>::DestructuringAssignment Pair;
+  const List<Pair>& assignments = func->destructuring_assignments_to_rewrite();
+  for (int i = assignments.length() - 1; i >= 0; --i) {

[adamk, 2015/11/20 22:42:58]

Any particular reason for iterating backwards here?

+    Pair pair = assignments.at(i);
+    Assignment* to_rewrite = pair.assignment->AsAssignment();
+    Scope* scope = pair.scope;
+    AssignmentPattern* pattern = to_rewrite->target()->AsAssignmentPattern();
+    if (pattern && !pattern->is_rewritten()) {
+      bool ok = true;
+      PatternRewriter::RewriteDestructuringAssignment(this, to_rewrite, scope,
+                                                      &ok);
+      DCHECK(ok);
+    }
+  }
+}
+
+
+Expression* ParserTraits::RewriteDestructuringAssignmentExpression(
+    Expression* expression) {
+  return parser_->RewriteDestructuringAssignmentExpression(expression);
+}
+
+
+void ParserTraits::ShouldRewriteDestructuringAssignment(Expression* expr) {

[adamk, 2015/11/20 22:42:58]

The name of this function doesn't make sense to me. Perhaps 
"QueueDestructuringAssignmentForRewriting"? "Should" prefix suggests a const
method that answers a question. 

+  DCHECK(expr->IsAssignment());

[adamk, 2015/11/20 22:42:58]

Why can't this method just take an Assignment* to avoid this DCHECK?

+  Assignment* assignment = expr->AsAssignment();
+  DCHECK(assignment->target()->IsAssignmentPattern());
+  DCHECK_EQ(Token::ASSIGN, assignment->op());
+  parser_->function_state_->AddDestructuringAssignment(
+      Parser::DestructuringAssignment(assignment, parser_->scope_));
+}
+
+inline void Parser::PatternRewriter::VisitObjectLiteral(ObjectLiteral* node) {

[adamk, 2015/11/20 22:42:58]

Can these methods move to the .cc file? Seems like this header's already plenty
big.

+  Variable* temp_var = nullptr;
+  VisitObjectLiteral(node, &temp_var);
+}
+
+inline void Parser::PatternRewriter::VisitArrayLiteral(ArrayLiteral* node) {
+  Variable* temp_var = nullptr;
+  VisitArrayLiteral(node, &temp_var);
+}
+
 }  // namespace internal
 }  // namespace v8