Properly collate multiple directory validation errors in scheduled_test.

pkg/scheduled_test/lib/src/descriptor/directory_descriptor.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 descriptor.file;
 
 import 'dart:async';
 import 'dart:io';
 
 import '../../../../../pkg/pathos/lib/path.dart' as path;
@@ skipping 25 matching lines @@
   Future validate([String parent]) => schedule(() => validateNow(parent),
       'validating directory:\n${describe()}');
 
   Future validateNow([String parent]) {
     if (parent == null) parent = defaultRoot;
     var fullPath = path.join(parent, name);
     if (!new Directory(fullPath).existsSync()) {
       throw "Directory not found: '$fullPath'.";
     }
 
-    return Future.wait(
-        contents.map((entry) => entry.validateNow(fullPath)).toList());
+    return Future.wait(contents.map((entry) {
+      return new Future.of(() => entry.validateNow(fullPath))
+          .then((_) => null)
+          .catchError((e) => e.error);
+    })).then((results) {
+      var errors = results.where((e) => e != null);
+      if (errors.isEmpty) return;
+      throw _DirectoryValidationError.merge(errors);
+    });
   }
 
   Stream<List<int>> load(String pathToLoad) {
     return futureStream(new Future.immediate(null).then((_) {
       if (_path.isAbsolute(pathToLoad)) {
         throw "Can't load absolute path '$pathToLoad'.";
       }
 
       var split = _path.split(_path.normalize(pathToLoad));
       if (split.isEmpty || split.first == '.' || split.first == '..') {
@@ skipping 31 matching lines @@
           .replaceFirst('|   ', '|-- ');
       buffer.writeln(entryString);
     }
 
     var lastEntryString = prefixLines(contents.last.describe(), prefix: '    ')
         .replaceFirst('    ', "'-- ");
     buffer.write(lastEntryString);
     return buffer.toString();
   }
 }
+
+/// A class for formatting errors thrown by [DirectoryDescriptor].
+class _DirectoryValidationError {
+  final Collection<String> errors;
+
+  /// Flatten nested [_DirectoryValidationError]s in [errors] to create a single
+  /// list of errors.
+  static _DirectoryValidationError merge(Iterable errors) {
+    return new _DirectoryValidationError(errors.expand((error) {
+      if (error is _DirectoryValidationError) return error.errors;
+      return [error];
+    }));
+  }
+
+  _DirectoryValidationError(Iterable errors)
+      : errors = errors.map((e) => e.toString()).toList();
+
+  String toString() {
+    if (errors.length == 1) return errors.single;
+    return errors.map((e) => prefixLines(e, prefix: '  ', firstPrefix: '* '))
+        .join('\n');
+  }
+}