Don't add the catch frame at a rethrow to the stacktrace.

runtime/vm/exceptions.cc

 // Copyright (c) 2011, 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/exceptions.h"
 
 #include "vm/dart_api_impl.h"
 #include "vm/dart_entry.h"
 #include "vm/debugger.h"
 #include "vm/flags.h"
@@ skipping 357 matching lines @@
   const Stacktrace& full_stacktrace = Stacktrace::Handle(
       Stacktrace::New(full_code_array, full_pc_offset_array));
   full_stacktrace.SetCatchStacktrace(full_catch_code_array,
                                      full_catch_pc_offset_array);
   return full_stacktrace.raw();
 }
 
 
 static void ThrowExceptionHelper(Isolate* isolate,
                                  const Instance& incoming_exception,
-                                 const Instance& existing_stacktrace) {
+                                 const Instance& existing_stacktrace,
+                                 const bool is_rethrow) {
+  ASSERT(existing_stacktrace.IsNull() == !is_rethrow);
   bool use_preallocated_stacktrace = false;
   Instance& exception = Instance::Handle(isolate, incoming_exception.raw());
   if (exception.IsNull()) {
     exception ^= Exceptions::Create(Exceptions::kNullThrown,
                                     Object::empty_array());
   } else if (exception.raw() == isolate->object_store()->out_of_memory() ||
              exception.raw() == isolate->object_store()->stack_overflow()) {
     use_preallocated_stacktrace = true;
   }
   uword handler_pc = 0;
@@ skipping 40 matching lines @@
     if (handler_needs_stacktrace) {
       RegularStacktraceBuilder frame_builder(false);
       BuildStackTrace(isolate, &frame_builder);
 
       // Create arrays for code and pc_offset tuples of each frame.
       code_array = Array::MakeArray(frame_builder.code_list());
       pc_offset_array = Array::MakeArray(frame_builder.pc_offset_list());
     }
     if (existing_stacktrace.IsNull()) {
       stacktrace = Stacktrace::New(code_array, pc_offset_array);
     } else {

[siva, 2014/06/25 22:46:12]

How about moving the assert on top to here as
ASSERT(is_rethrow);

       stacktrace ^= existing_stacktrace.raw();
       if (pc_offset_array.Length() != 0) {
-        stacktrace.Append(code_array, pc_offset_array);
+        // Skip the first frame during a rethrow. This is the catch clause with
+        // the rethrow statement, which is not part of the original trace a
+        // rethrow is supposed to preserve.
+        const intptr_t offset = is_rethrow ? 1 : 0;

[siva, 2014/06/25 22:46:12]

Can this just be:
const intptr_t offset = 1;
since we have asserted that it is always a rethrow in this case.

[rmacnak, 2014/06/25 23:00:43]

Ah, yes.

+        stacktrace.Append(code_array, pc_offset_array, offset);
       }
       // Since we are re throwing and appending to the existing stack trace
       // we clear out the catch trace collected in the existing stack trace
       // as that trace will not be valid anymore.
       stacktrace.SetCatchStacktrace(Object::empty_array(),
                                     Object::empty_array());
     }
   }
   // We expect to find a handler_pc, if the exception is unhandled
   // then we expect to at least have the dart entry frame on the
@@ skipping 114 matching lines @@
   }
   // Throw TypeError or CastError instance.
   Exceptions::ThrowByType(exception_type, args);
   UNREACHABLE();
 }
 
 
 void Exceptions::Throw(Isolate* isolate, const Instance& exception) {
   isolate->debugger()->SignalExceptionThrown(exception);
   // Null object is a valid exception object.
-  ThrowExceptionHelper(isolate, exception, Instance::Handle(isolate));
+  ThrowExceptionHelper(isolate, exception, Instance::Handle(isolate), false);
 }
 
 
 void Exceptions::ReThrow(Isolate* isolate,
                          const Instance& exception,
                          const Instance& stacktrace) {
   // Null object is a valid exception object.
-  ThrowExceptionHelper(isolate, exception, stacktrace);
+  ThrowExceptionHelper(isolate, exception, stacktrace, true);
 }
 
 
 void Exceptions::PropagateError(const Error& error) {
   Isolate* isolate = Isolate::Current();
   ASSERT(isolate->top_exit_frame_info() != 0);
   if (error.IsUnhandledException()) {
     // If the error object represents an unhandled exception, then
     // rethrow the exception in the normal fashion.
     const UnhandledException& uhe = UnhandledException::Cast(error);
@@ skipping 147 matching lines @@
 
 // Throw JavascriptCompatibilityError exception.
 void Exceptions::ThrowJavascriptCompatibilityError(const char* msg) {
   const Array& exc_args = Array::Handle(Array::New(1));
   const String& msg_str = String::Handle(String::New(msg));
   exc_args.SetAt(0, msg_str);
   Exceptions::ThrowByType(Exceptions::kJavascriptCompatibilityError, exc_args);
 }
 
 }  // namespace dart