Support transforming the exception in Future.transform().

lib/coreimpl/future_implementation.dart

Index: lib/coreimpl/future_implementation.dart
diff --git a/lib/coreimpl/future_implementation.dart b/lib/coreimpl/future_implementation.dart
index 328c88964c6be89f44914b7bdddb32a12102758e..52453b1eea5eb0f125e4db3c0cd0dab7d0521360 100644
--- a/lib/coreimpl/future_implementation.dart
+++ b/lib/coreimpl/future_implementation.dart
@@ -171,10 +171,12 @@ class FutureImpl<T> implements Future<T> {
 
   Future transform(Function transformation) {
     final completer = new Completer();
-    handleException((e) {
-      completer.completeException(e, this.stackTrace);
+
+    handleException((ex) {

[nweiz, 2012/09/04 20:26:14]

Why are you renaming this to "ex"? "catch (e)" is much more widely used in Dart
code.

[Bob Nystrom, 2012/09/04 21:14:43]

Stale change. Removed.

+      completer.completeException(ex, stackTrace);
       return true;
     });
+
     then((v) {
       var transformed = null;
       try {
@@ -185,6 +187,7 @@ class FutureImpl<T> implements Future<T> {
       }
       completer.complete(transformed);
     });
+
     return completer.future;
   }
 
@@ -210,6 +213,31 @@ class FutureImpl<T> implements Future<T> {
     });
     return completer.future;
   }
+
+  Future transformException(bool transformation(Object exception)) {
+    final completer = new Completer();
+
+    handleException((ex) {
+      var result = false;
+      var resultStackTrace = stackTrace;
+      try {
+        result = transformation(ex);
+      } catch (innerException, innerStackTrace) {
+        ex = innerException;
+        resultStackTrace = innerStackTrace;
+      }
+
+      if (result != true) {
+        completer.completeException(ex, resultStackTrace);
+      }
+
+      return true;
+    });
+
+    then(completer.complete);
+
+    return completer.future;
+  }
 }
 
 class CompleterImpl<T> implements Completer<T> {