Preserve exception message in iterator finalization.

src/parsing/parser.cc

Index: src/parsing/parser.cc
diff --git a/src/parsing/parser.cc b/src/parsing/parser.cc
index e3063d8b1fc251ddc5b493391e5fbb858ad097ad..ab19fd202f3373ff178b865501832308c8c8de60 100644
--- a/src/parsing/parser.cc
+++ b/src/parsing/parser.cc
@@ -3007,9 +3007,9 @@ TryStatement* Parser::ParseTryStatement(bool* ok) {
   if (catch_block != NULL && finally_block != NULL) {
     // If we have both, create an inner try/catch.
     DCHECK(catch_scope != NULL && catch_variable != NULL);
-    TryCatchStatement* statement =
-        factory()->NewTryCatchStatement(try_block, catch_scope, catch_variable,
-                                        catch_block, RelocInfo::kNoPosition);
+    TryCatchStatement* statement = factory()->NewTryCatchStatement(
+        try_block, catch_scope, catch_variable, catch_block, true,
+        RelocInfo::kNoPosition);
     try_block = factory()->NewBlock(NULL, 1, false, RelocInfo::kNoPosition);
     try_block->statements()->Add(statement, zone());
     catch_block = NULL;  // Clear to indicate it's been handled.
@@ -3024,8 +3024,8 @@ TryStatement* Parser::ParseTryStatement(bool* ok) {
 
     DCHECK(finally_block == NULL);
     DCHECK(catch_scope != NULL && catch_variable != NULL);
-    result = factory()->NewTryCatchStatement(try_block, catch_scope,
-                                             catch_variable, catch_block, pos);
+    result = factory()->NewTryCatchStatement(
+        try_block, catch_scope, catch_variable, catch_block, true, pos);
   } else {
     DCHECK(finally_block != NULL);
     result = factory()->NewTryFinallyStatement(try_block, finally_block, pos);
@@ -6058,7 +6058,7 @@ Expression* ParserTraits::RewriteYieldStar(
                                                Variable::NORMAL);
 
     try_catch = factory->NewTryCatchStatement(
-        try_block, catch_scope, catch_variable, catch_block, nopos);
+        try_block, catch_scope, catch_variable, catch_block, true, nopos);
   }
 
 
@@ -6464,7 +6464,7 @@ void ParserTraits::FinalizeIteratorUse(Variable* completion,
   //       iterator_use
   //     } catch(e) {
   //       if (completion === kAbruptCompletion) completion = kThrowCompletion;
-  //       throw e;
+  //       %ReThrow(e);
   //     }
   //   } finally {
   //     if (condition) {
@@ -6525,7 +6525,7 @@ void ParserTraits::FinalizeIteratorUse(Variable* completion,
   // try { #try_block }
   // catch(e) {
   //   #set_completion_throw;
-  //   throw e;
+  //   %ReThrow(e);
   // }
   Statement* try_catch;
   {
@@ -6535,10 +6535,14 @@ void ParserTraits::FinalizeIteratorUse(Variable* completion,
                                   kCreatedInitialized, Variable::NORMAL);
 
     Statement* rethrow;
+    // We use %ReThrow rather than the ordinary throw because we want to
+    // keep the original exception message.  This is also why we create the
+    // TryCatchStatement below with clear_pending_message set to false.
     {
-      Expression* proxy = factory->NewVariableProxy(catch_variable);
-      rethrow = factory->NewExpressionStatement(factory->NewThrow(proxy, nopos),
-                                                nopos);
+      auto args = new (zone) ZoneList<Expression*>(1, zone);
+      args->Add(factory->NewVariableProxy(catch_variable), zone);
+      rethrow = factory->NewExpressionStatement(
+          factory->NewCallRuntime(Runtime::kReThrow, args, nopos), nopos);
     }
 
     Block* catch_block = factory->NewBlock(nullptr, 2, false, nopos);
@@ -6546,7 +6550,7 @@ void ParserTraits::FinalizeIteratorUse(Variable* completion,
     catch_block->statements()->Add(rethrow, zone);
 
     try_catch = factory->NewTryCatchStatement(
-        iterator_use, catch_scope, catch_variable, catch_block, nopos);
+        iterator_use, catch_scope, catch_variable, catch_block, false, nopos);
   }
 
   // try { #try_catch } finally { #maybe_close }
@@ -6641,7 +6645,7 @@ void ParserTraits::BuildIteratorCloseForCompletion(
         Variable::NORMAL);
 
     try_call_return = factory->NewTryCatchStatement(
-        try_block, catch_scope, catch_variable, catch_block, nopos);
+        try_block, catch_scope, catch_variable, catch_block, true, nopos);
   }
 
   // let output = %_Call(iteratorReturn, iterator);
@@ -6741,7 +6745,7 @@ Statement* ParserTraits::FinalizeForOfStatement(ForOfStatement* loop, int pos) {
   //       #loop;
   //     } catch(e) {
   //       if (completion === kAbruptCompletion) completion = kThrowCompletion;
-  //       throw e;
+  //       %ReThrow(e);
   //     }
   //   } finally {
   //     if (!(completion === kNormalCompletion || IS_UNDEFINED(#iterator))) {