Properly capture and pass the stack trace in Future exceptions.

corelib/src/implementation/future_implementation.dart

 // Copyright 2012 Google Inc. All Rights Reserved.
 // Dart core library.
 
 class FutureImpl<T> implements Future<T> {
 
   bool _isComplete = false;
 
   /**
    * Value that was provided to this Future by the Completer
    */
@@ skipping 154 matching lines @@
       throw new FutureAlreadyCompleteException();
     }
     _exception = exception;
     _stackTrace = stackTrace;
     _complete();
   }
 
   Future transform(Function transformation) {
     final completer = new Completer();
     handleException((e) {
-      completer.completeException(e);
+      completer.completeException(e, this.stackTrace);
       return true;
     });
     then((v) {
       var transformed = null;
       try {
         transformed = transformation(v);
-      } catch (final ex, final stackTrace) {
+      } catch (Exception ex, final stackTrace) {

[Siggi Cherem (dart-lang), 2012/07/03 19:13:46]

weird, why is this needed? what if it was 'var' or we omit any annotation here?

[nweiz, 2012/07/03 21:39:26]

With "var" or "final", the stack trace isn't captured. "catch (ex" doesn't
compile at all. Only "Exception" works. I have no idea why this is the case.

[Siggi Cherem (dart-lang), 2012/07/03 22:10:06]

weird... if you haven't already, file a bug on the VM about this issue. 

         completer.completeException(ex, stackTrace);
         return;
       }
       completer.complete(transformed);
     });
     return completer.future;
   }
 
   Future chain(Function transformation) {
     final completer = new Completer();
     handleException((e) {
-      completer.completeException(e);
+      completer.completeException(e, this.stackTrace);
       return true;
     });
     then((v) {
       var future = null;
       try {
         future = transformation(v);
-      } catch (final ex, final stackTrace) {
+      } catch (Exception ex, final stackTrace) {
         completer.completeException(ex, stackTrace);
         return;
       }
       future.handleException((e) {
-        completer.completeException(e);
+        completer.completeException(e, this.stackTrace);
         return true;
       });
       future.then((b) => completer.complete(b));
     });
     return completer.future;
   }
 }
 
 class CompleterImpl<T> implements Completer<T> {
 
   final FutureImpl<T> _futureImpl;
 
   CompleterImpl() : _futureImpl = new FutureImpl() {}
 
   Future<T> get future() {
     return _futureImpl;
   }
 
   void complete(T value) {
     _futureImpl._setValue(value);
   }
 
   void completeException(Object exception, [Object stackTrace]) {
     _futureImpl._setException(exception, stackTrace);
   }
 }