Add more metadata to non-programmatic barback exceptions.

pkg/barback/lib/src/utils.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 barback.utils;
 
 import 'dart:async';
 
+/// A pair of values.
+class Pair<E, F> {
+  E first;
+  F last;
+
+  Pair(this.first, this.last);
+
+  String toString() => '($first, $last)';
+
+  bool operator==(other) {
+    if (other is! Pair) return false;
+    return other.first == first && other.last == last;
+  }
+
+  int get hashCode => first.hashCode ^ last.hashCode;
+}
+
 /// Converts a number in the range [0-255] to a two digit hex string.
 ///
 /// For example, given `255`, returns `ff`.
 String byteToHex(int byte) {
   assert(byte >= 0 && byte <= 255);
 
   const DIGITS = "0123456789abcdef";
   return DIGITS[(byte ~/ 16) % 16] + DIGITS[byte % 16];
 }
 
@@ skipping 20 matching lines @@
         helper(element);
       } else {
         result.add(element);
       }
     }
   }
   helper(nested);
   return result;
 }
 
+/// Returns the union of all elements in each set in [sets].
+Set unionAll(Iterable<Set> sets) =>
+  sets.fold(new Set(), (union, set) => union.union(set));
+
 /// Passes each key/value pair in [map] to [fn] and returns a new [Map] whose
 /// values are the return values of [fn].
 Map mapMapValues(Map map, fn(key, value)) =>
   new Map.fromIterable(map.keys, value: (key) => fn(key, map[key]));
 
 /// Merges [streams] into a single stream that emits events from all sources.
 Stream mergeStreams(Iterable<Stream> streams) {
   streams = streams.toList();
   var doneCount = 0;
   // Use a sync stream to preserve the synchrony behavior of the input streams.
@@ skipping 38 matching lines @@
   // We use a delayed future to allow runAsync events to finish. The
   // Future.value or Future() constructors use runAsync themselves and would
   // therefore not wait for runAsync callbacks that are scheduled after invoking
   // this method.
   return new Future.delayed(Duration.ZERO, () => pumpEventQueue(times - 1));
 }
 
 /// Like [new Future], but avoids issue 11911 by using [new Future.value] under
 /// the covers.
 Future newFuture(callback()) => new Future.value().then((_) => callback());