Fix issue 21795.

runtime/vm/code_descriptors.h

 // Copyright (c) 2012, 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.
 
 #ifndef VM_CODE_DESCRIPTORS_H_
 #define VM_CODE_DESCRIPTORS_H_
 
 #include "vm/ast.h"
 #include "vm/code_generator.h"
 #include "vm/globals.h"
@@ skipping 117 matching lines @@
                   const Array& handler_types,
                   bool needs_stacktrace) {
     ASSERT(try_index >= 0);
     while (Length() <= try_index) {
       AddPlaceHolder();
     }
     list_[try_index].outer_try_index = outer_try_index;
     list_[try_index].pc_offset = pc_offset;
     ASSERT(handler_types.IsZoneHandle());
     list_[try_index].handler_types = &handler_types;
     list_[try_index].needs_stacktrace = needs_stacktrace;

[regis, 2015/01/10 00:58:16]

I rushed to catch my shuttle and I realize now (on the shuttle) that this could
overwrite a 'true' value set earlier by SetNeedsStacktrace, or would the correct
value be passed in this case?

I will let you decide of the proper fix, since I cannot debug from the shuttle
and more importantly since you understand this much better than me. Thanks!

[Florian Schneider, 2015/01/12 12:47:48]

You're right. The flag may be overridden, so AddHandler needs to check here if
it is already set. Otherwise, the stacktrace of the re-thrown exception will be
wrong. I attached a regression test to the issue.

   }
 
 
   // Called by rethrows, to mark their enclosing handlers.
   void SetNeedsStacktrace(intptr_t try_index) {
     // Rethrows can be generated outside a try by the compiler.
     if (try_index == CatchClauseNode::kInvalidTryIndex) {
       return;
     }
-    ASSERT((0 <= try_index) && (try_index < Length()));
+    ASSERT(try_index >= 0);
+    while (Length() <= try_index) {
+      AddPlaceHolder();
+    }
     list_[try_index].needs_stacktrace = true;
   }
 
 
   static bool ContainsDynamic(const Array& array) {
     for (intptr_t i = 0; i < array.Length(); i++) {
       if (array.At(i) == Type::DynamicType()) {
         return true;
       }
     }
@@ skipping 23 matching lines @@
   }
 
  private:
   GrowableArray<struct HandlerDesc> list_;
   DISALLOW_COPY_AND_ASSIGN(ExceptionHandlerList);
 };
 
 }  // namespace dart
 
 #endif  // VM_CODE_DESCRIPTORS_H_