Make padding consistent across all stack traces for Chain.toString().

lib/src/chain.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 stack_trace.chain;
 
 import 'dart:async';
 import 'dart:collection';
+import 'dart:math' as math;
 
 import 'frame.dart';
 import 'stack_zone_specification.dart';
 import 'trace.dart';
 import 'utils.dart';
 
 /// A function that handles errors in the zone wrapped by [Chain.capture].
 typedef void ChainHandler(error, Chain chain);
 
+/// The line used in the string representation of stack chains to represent
+/// the gap between traces.
+const _gap = '===== asynchronous gap ===========================\n';
+
 /// A chain of stack traces.
 ///
 /// A stack chain is a collection of one or more stack traces that collectively
 /// represent the path from [main] through nested function calls to a particular
 /// code location, usually where an error was thrown. Multiple stack traces are
 /// necessary when using asynchronous functions, since the program's stack is
 /// reset before each asynchronous callback is run.
 ///
 /// Stack chains can be automatically tracked using [Chain.capture]. This sets
 /// up a new [Zone] in which the current stack chain is tracked and can be
 /// accessed using [new Chain.current]. Any errors that would be top-leveled in
 /// the zone can be handled, along with their associated chains, with the
 /// `onError` callback. For example:
 ///
 ///     Chain.capture(() {
 ///       // ...
 ///     }, onError: (error, stackChain) {
 ///       print("Caught error $error\n"
 ///             "$stackChain");
 ///     });
 class Chain implements StackTrace {
-  /// The line used in the string representation of stack chains to represent
-  /// the gap between traces.
-  static const _GAP = '===== asynchronous gap ===========================\n';
 
   /// The stack traces that make up this chain.
   ///
   /// Like the frames in a stack trace, the traces are ordered from most local
   /// to least local. The first one is the trace where the actual exception was
   /// raised, the second one is where that callback was scheduled, and so on.
   final List<Trace> traces;
 
   /// The [StackZoneSpecification] for the current zone.
   static StackZoneSpecification get _currentSpec =>
@@ skipping 121 matching lines @@
 
     return new Chain(nonEmptyTraces);
   }
 
   /// Converts [this] to a [Trace].
   ///
   /// The trace version of a chain is just the concatenation of all the traces
   /// in the chain.
   Trace toTrace() => new Trace(flatten(traces.map((trace) => trace.frames)));
 
-  String toString() => traces.join(_GAP);
+  String toString() {
+    // Figure out the longest path so we know how much to pad.
+    var longest = traces.map((trace) {
+      return trace.frames.map((frame) => frame.location.length)
+          .fold(0, math.max);
+    }).fold(0, math.max);
+
+    // Don't call out to [Trace.toString] here because that doesn't ensure that
+    // padding is consistent across all traces.
+    return traces.map((trace) {
+      return trace.frames.map((frame) {
+        return '${padRight(frame.location, longest)}  ${frame.member}\n';
+      }).join();
+    }).join(_gap);
+  }
 }