Produce useful error messages for empty pubspecs.

BUG=20103
R=blois@google.com

Review URL: https://codereview.chromium.org//417023002

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@38565 260f80e4-7a28-3924-810f-c04153c831b5

lib/src/pubspec.dart

@@ -273,11 +273,9 @@ class Pubspec {
   /// [Version.none].
   factory Pubspec.parse(String contents, SourceRegistry sources,
       {String expectedName, Uri location}) {
-    if (contents.trim() == '') return new Pubspec.empty();
-
     var pubspecNode = loadYamlNode(contents, sourceUrl: location);
     if (pubspecNode is YamlScalar && pubspecNode.value == null) {
-      pubspecNode = new YamlMap();
+      pubspecNode = new YamlMap(sourceUrl: location);
     } else if (pubspecNode is! YamlMap) {
       throw new PubspecException(
           'The pubspec must be a YAML mapping.', pubspecNode.span);

test/get/path/empty_pubspec_test.dart

+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS d.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 d.file.
+
+import 'package:path/path.dart' as p;
+
+import '../../../lib/src/exit_codes.dart' as exit_codes;
+import '../../descriptor.dart' as d;
+import '../../test_pub.dart';
+
+main() {
+  initConfig();
+  // Regression test for issue 20103.
+  integration('path dependency to an empty pubspec', () {
+    d.dir('foo', [
+      d.libDir('foo'),
+      d.file('pubspec.yaml', '')
+    ]).create();
+
+    d.dir(appPath, [
+      d.appPubspec({
+        "foo": {"path": "../foo"}
+      })
+    ]).create();
+
+    pubGet(exitCode: exit_codes.DATA, error:
+        'Error on line 1, column 1 of ${p.join('..', 'foo', 'pubspec.yaml')}: '
+            'Missing the required "name" field.');
+  });
+}
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