Add new constructors to YamlNode subclasses.

pkg/yaml/lib/src/dummy_span.dart

+// Copyright (c) 2014, 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 yaml.dummy_span;
+
+import 'package:path/path.dart' as p;
+import 'package:source_maps/source_maps.dart';
+
+/// A [Span] with no location information.
+///
+/// This is used with [YamlMap.wrap] and [YamlList.wrap] to provide means of
+/// accessing a non-YAML map that behaves transparently like a map parsed from
+/// YAML.
+class DummySpan extends Span {

[Bob Nystrom, 2014/06/21 00:14:15]

How about "Dummy" -> "Null"?

It's effectively the null object pattern, and "dummy" has mocking or testing
implications to me.

[nweiz, 2014/06/23 22:23:06]

Done.

+  Location get end => start;
+  final text = "";
+
+  DummySpan(String sourceUrl)
+      : this._(new DummyLocation(sourceUrl));
+
+  DummySpan._(Location location)

[Bob Nystrom, 2014/06/21 00:14:15]

What's this constructor for?

[nweiz, 2014/06/23 22:23:06]

The superclass constructor requires two locations, but we want to pass the same
object for both. This constructor exists so the previous constructor can pass it
a location that it can then use twice.

Basically, it's a band-aid for Dart's inability to use local variables in
initializer lists.

[Bob Nystrom, 2014/06/23 23:11:44]

Oh, I see it now. Thanks.

+      : super(location, location, false);
+
+  String formatLocationMessage(String message, {bool useColors: false,
+      String color}) {
+    var locationMessage = sourceUrl == null ? "in an unknown location" :
+        "in ${p.prettyUri(sourceUrl)}";
+    return "$locationMessage: $message";
+  }
+}
+
+/// A [Location] with no location information.
+///
+/// This is used with [YamlMap.wrap] and [YamlList.wrap] to provide means of
+/// accessing a non-YAML map that behaves transparently like a map parsed from
+/// YAML.
+class DummyLocation extends Location {
+  final String sourceUrl;
+  final line = 0;
+  final column = 0;
+
+  String get formatString => sourceUrl == null ? "unknown location" : sourceUrl;
+
+  DummyLocation(this.sourceUrl)
+      : super(0);
+}