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

src/rewriter.cc

Index: src/rewriter.cc
diff --git a/src/rewriter.cc b/src/rewriter.cc
index 2de25407e3fe608bb95857be826023be69b83ac4..bd4630c0923e683739d6d0d30ecf835b046b827b 100644
--- a/src/rewriter.cc
+++ b/src/rewriter.cc
@@ -49,6 +49,9 @@ class Processor: public AstVisitor {
         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)
@@ -60,6 +63,20 @@ class Processor: public AstVisitor {
 };
 
 
+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));
@@ -103,6 +120,11 @@ void Processor::VisitIfStatement(IfStatement* node) {
   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);
+  }
 }
 
 
@@ -114,6 +136,11 @@ void Processor::VisitIterationStatement(IterationStatement* node) {
   node->set_body(replacement_);
   is_set_ = is_set_ && set_after;
   replacement_ = node;
+
+  if (FLAG_harmony_completion && !is_set_) {
+    is_set_ = true;
+    replacement_ = AssignUndefinedBefore(node);
+  }
 }
 
 
@@ -153,6 +180,11 @@ void Processor::VisitTryCatchStatement(TryCatchStatement* node) {
   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);
+  }
 }
 
 
@@ -163,6 +195,11 @@ void Processor::VisitTryFinallyStatement(TryFinallyStatement* node) {
   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);
+  }
 }
 
 
@@ -176,6 +213,11 @@ void Processor::VisitSwitchStatement(SwitchStatement* node) {
   }
   is_set_ = is_set_ && set_after;
   replacement_ = node;
+
+  if (FLAG_harmony_completion && !is_set_) {
+    is_set_ = true;
+    replacement_ = AssignUndefinedBefore(node);
+  }
 }
 
 
@@ -195,6 +237,11 @@ 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);
+  }
 }