Fix issue 22875

runtime/vm/ast_transformer.cc

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/ast_transformer.h"
 
 #include "vm/object_store.h"
 #include "vm/parser.h"
 #include "vm/thread.h"
 
@@ skipping 583 matching lines @@
   LocalVariable* result = AddToPreambleNewTempVar(
       new(Z) AssignableNode(node->token_pos(),
                             new_expr,
                             node->type(),
                             node->dst_name()));
   result_ = new(Z) LoadLocalNode(Scanner::kNoSourcePos, result);
 }
 
 
 void AwaitTransformer::VisitLetNode(LetNode* node) {
-  // Add all the initializer nodes and their temporary variables
-  // to the preamble. The temporary variables will be captured
-  // as a side effect of being added to a scope, and the subsequent
-  // nodes that are added to the preample can access them.
+  // Add all the initializer nodes to the preamble and the
+  // temporary variables to the scope for async temporary variables.
+  // The temporary variables will be captured as a side effect of being
+  // added to a scope, and the subsequent nodes that are added to the
+  // preample can access them.
   for (intptr_t i = 0; i < node->num_temps(); i++) {
-    preamble_->scope()->AddVariable(node->TempAt(i));
+    function_top_->AddVariable(node->TempAt(i));
     AstNode* new_init_val = Transform(node->InitializerAt(i));
     preamble_->Add(new(Z) StoreLocalNode(node->token_pos(),
                    node->TempAt(i),
                    new_init_val));
   }
   // The transformed LetNode does not have any temporary variables.
   LetNode* result = new(Z) LetNode(node->token_pos());
   for (intptr_t i = 0; i < node->nodes().length(); i++) {
     result->AddNode(Transform(node->nodes()[i]));
   }
   result_ = result;
 }
 
 
 void AwaitTransformer::VisitThrowNode(ThrowNode* node) {
   AstNode* new_exception = Transform(node->exception());
   result_ = new(Z) ThrowNode(node->token_pos(),
                              new_exception,
                              node->stacktrace());
 }
 
 }  // namespace dart