Fold empty async frames when generating a terse stack trace.

lib/src/trace.dart

 // Copyright (c) 2013, 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.
 
 library trace;
 
 import 'dart:collection';
 import 'dart:math' as math;
 
 import 'chain.dart';
@@ skipping 187 matching lines @@
   StackTrace get vmTrace => new VMTrace(frames);
 
   /// Returns a terser version of [this].
   ///
   /// This is accomplished by folding together multiple stack frames from the
   /// core library or from this package, as in [foldFrames]. Remaining core
   /// library frames have their libraries, "-patch" suffixes, and line numbers
   /// removed.
   Trace get terse {
     return new Trace(foldFrames((frame) {
-      return frame.isCore || frame.package == 'stack_trace';
+      if (frame.isCore) return true;
+      if (frame.package == 'stack_trace') return true;
+
+      // Ignore async stack frames without any line or column information. These
+      // come from the VM's async/await implementation and represent internal
+      // frames. They only ever show up in stack chains and are always
+      // surrounded by other traces that are actually useful, so we can just get
+      // rid of them.
+      // TODO(nweiz): Get rid of this logic some time after issue 22009 is
+      // fixed.
+      if (!frame.member.contains('<async>')) return false;
+      return frame.line == null;
     }).frames.map((frame) {
       if (!frame.isCore) return frame;
       var library = frame.library.replaceAll(_terseRegExp, '');
       return new Frame(Uri.parse(library), null, null, frame.member);
     }));
   }
 
   /// Returns a new [Trace] based on [this] where multiple stack frames matching
   /// [predicate] are folded together. This means that whenever there are
   /// multiple frames in a row that match [predicate], only the last one is
@@ skipping 20 matching lines @@
     // Figure out the longest path so we know how much to pad.
     var longest = frames.map((frame) => frame.location.length)
         .fold(0, math.max);
 
     // Print out the stack trace nicely formatted.
     return frames.map((frame) {
       return '${padRight(frame.location, longest)}  ${frame.member}\n';
     }).join();
   }
 }