Implement ES6 completion semantics (--harmony-completion).

src/rewriter.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/rewriter.h"
 
 #include "src/ast.h"
 #include "src/parser.h"
 #include "src/scopes.h"
 
@@ skipping 31 matching lines @@
   bool is_set_;
 
   AstNodeFactory factory_;
 
   Expression* SetResult(Expression* value) {
     VariableProxy* result_proxy = factory()->NewVariableProxy(result_);
     return factory()->NewAssignment(
         Token::ASSIGN, result_proxy, value, RelocInfo::kNoPosition);
   }
 
+  // Inserts '.result = undefined' in front of the given statement.
+  Statement* AssignUndefinedBefore(Statement* s);
+
   // Node visitors.
 #define DEF_VISIT(type) virtual void Visit##type(type* node) override;
   AST_NODE_LIST(DEF_VISIT)
 #undef DEF_VISIT
 
   void VisitIterationStatement(IterationStatement* stmt);
 
   DEFINE_AST_VISITOR_SUBCLASS_MEMBERS();
 };
 
 
+Statement* Processor::AssignUndefinedBefore(Statement* s) {
+  Expression* result_proxy = factory()->NewVariableProxy(result_);
+  Expression* undef = factory()->NewUndefinedLiteral(RelocInfo::kNoPosition);
+  Expression* assignment = factory()->NewAssignment(
+      Token::ASSIGN, result_proxy, undef, RelocInfo::kNoPosition);
+  Block* b = factory()->NewBlock(NULL, 2, false, RelocInfo::kNoPosition);
+  b->AddStatement(
+      factory()->NewExpressionStatement(assignment, RelocInfo::kNoPosition),
+      zone());
+  b->AddStatement(s, zone());
+  return b;
+}
+
+
 void Processor::Process(ZoneList<Statement*>* statements) {
   for (int i = statements->length() - 1; i >= 0; --i) {
     Visit(statements->at(i));
     statements->Set(i, replacement_);
   }
 }
 
 
 void Processor::VisitBlock(Block* node) {
   // An initializer block is the rewritten form of a variable declaration
@@ skipping 23 matching lines @@
   // Rewrite both branches.
   bool set_after = is_set_;
   Visit(node->then_statement());
   node->set_then_statement(replacement_);
   bool set_in_then = is_set_;
   is_set_ = set_after;
   Visit(node->else_statement());
   node->set_else_statement(replacement_);
   is_set_ = is_set_ && set_in_then;
   replacement_ = node;
+
+  if (FLAG_harmony_completion && !is_set_) {
+    is_set_ = true;

[rossberg, 2015/09/28 14:09:22]

Why not move this into AssignUndefinedBeforeNode?

[neis, 2015/10/05 10:57:28]

I prefer the is_set_ logic to be explicit in the Visit functions.

+    replacement_ = AssignUndefinedBefore(node);
+  }
 }
 
 
 void Processor::VisitIterationStatement(IterationStatement* node) {
   // Rewrite the body.
   bool set_after = is_set_;
   is_set_ = false;  // We are in a loop, so we can't rely on [set_after].
   Visit(node->body());
   node->set_body(replacement_);
   is_set_ = is_set_ && set_after;
   replacement_ = node;
+
+  if (FLAG_harmony_completion && !is_set_) {
+    is_set_ = true;
+    replacement_ = AssignUndefinedBefore(node);
+  }
 }
 
 
 void Processor::VisitDoWhileStatement(DoWhileStatement* node) {
   VisitIterationStatement(node);
 }
 
 
 void Processor::VisitWhileStatement(WhileStatement* node) {
   VisitIterationStatement(node);
@@ skipping 19 matching lines @@
   // Rewrite both try and catch block.
   bool set_after = is_set_;
   Visit(node->try_block());
   node->set_try_block(static_cast<Block*>(replacement_));
   bool set_in_try = is_set_;
   is_set_ = set_after;
   Visit(node->catch_block());
   node->set_catch_block(static_cast<Block*>(replacement_));
   is_set_ = is_set_ && set_in_try;
   replacement_ = node;
+
+  if (FLAG_harmony_completion && !is_set_) {
+    is_set_ = true;
+    replacement_ = AssignUndefinedBefore(node);
+  }
 }
 
 
 void Processor::VisitTryFinallyStatement(TryFinallyStatement* node) {
   // Rewrite both try and finally block (in reverse order).
   Visit(node->finally_block());
   node->set_finally_block(static_cast<Block*>(replacement_));
   Visit(node->try_block());  // Exception will not be caught.
   node->set_try_block(static_cast<Block*>(replacement_));
   replacement_ = node;
+
+  if (FLAG_harmony_completion && !is_set_) {
+    is_set_ = true;
+    replacement_ = AssignUndefinedBefore(node);
+  }
 }
 
 
 void Processor::VisitSwitchStatement(SwitchStatement* node) {
   // Rewrite statements in all case clauses (in reverse order).
   ZoneList<CaseClause*>* clauses = node->cases();
   bool set_after = is_set_;
   for (int i = clauses->length() - 1; i >= 0; --i) {
     CaseClause* clause = clauses->at(i);
     Process(clause->statements());
   }
   is_set_ = is_set_ && set_after;
   replacement_ = node;
+
+  if (FLAG_harmony_completion && !is_set_) {
+    is_set_ = true;
+    replacement_ = AssignUndefinedBefore(node);
+  }
 }
 
 
 void Processor::VisitContinueStatement(ContinueStatement* node) {
   is_set_ = false;
   replacement_ = node;
 }
 
 
 void Processor::VisitBreakStatement(BreakStatement* node) {
   is_set_ = false;
   replacement_ = node;
 }
 
 
 void Processor::VisitWithStatement(WithStatement* node) {
   Visit(node->statement());
   node->set_statement(replacement_);
   replacement_ = node;
+
+  if (FLAG_harmony_completion && !is_set_) {
+    is_set_ = true;
+    replacement_ = AssignUndefinedBefore(node);
+  }
 }
 
 
 void Processor::VisitSloppyBlockFunctionStatement(
     SloppyBlockFunctionStatement* node) {
   Visit(node->statement());
   node->set_statement(replacement_);
   replacement_ = node;
 }
 
@@ skipping 61 matching lines @@
         processor.factory()->NewReturnStatement(result_proxy, pos);
     body->Add(result_statement, info->zone());
   }
 
   return true;
 }
 
 
 }  // namespace internal
 }  // namespace v8