Preserve the stack trace for rethrown exceptions in Future.transformException.

Review URL: https://codereview.chromium.org//11308281

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@15704 260f80e4-7a28-3924-810f-c04153c831b5

Author: nex3

sdk/lib/core/future_impl.dart

@@ -235,7 +235,11 @@ class _FutureImpl<T> implements Future<T> {
           completer.complete(result);
         }
       } catch (innerException, stackTrace) {
-        completer.completeException(innerException, stackTrace);
+        if (identical(ex, innerException)) {
+          completer.completeException(innerException, this.stackTrace);
+        } else {
+          completer.completeException(innerException, stackTrace);
+        }
       }
       return false;
     });

tests/corelib/future_test.dart

@@ -351,6 +351,19 @@ testCallStackIsCapturedIfChainCallbackThrows() {
   Expect.isNotNull(chained.stackTrace);
 }
 
+testCallStackIsPreservedIfExceptionIsRethrownInTransformException() {
+  final completer = new Completer();
+  var chained = completer.future.chain((_) {
+    throw 'whoops!';
+  });
+  var transformed = chained.transformException((e) {
+    throw e;
+  });
+
+  completer.complete('blah');
+  Expect.equals(transformed.stackTrace, chained.stackTrace);
+}
+
 // Tests for mixed usage of [onComplete], [then], and [handleException]
 
 testCompleteWithCompletionAndSuccessHandlers() {
@@ -677,6 +690,7 @@ main() {
   testCallStackReturnsCallstackPassedToCompleteException();
   testCallStackIsCapturedIfTransformCallbackThrows();
   testCallStackIsCapturedIfChainCallbackThrows();
+  testCallStackIsPreservedIfExceptionIsRethrownInTransformException();
   testCompleteWithCompletionAndSuccessHandlers();
   testExceptionWithCompletionAndSuccessHandlers();
   testExceptionWithCompletionAndSuccessAndExceptionHandlers();