Attach source range information to parsed YAML nodes.

pkg/yaml/lib/src/yaml_node.dart

Index: pkg/yaml/lib/src/yaml_node.dart
diff --git a/pkg/yaml/lib/src/yaml_node.dart b/pkg/yaml/lib/src/yaml_node.dart
new file mode 100644
index 0000000000000000000000000000000000000000..d0e0578995b5e9d8faf5fcd6d8202f6198dce8bb
--- /dev/null
+++ b/pkg/yaml/lib/src/yaml_node.dart
@@ -0,0 +1,92 @@
+// Copyright (c) 2012, 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.map;
+
+import 'dart:collection' as collection;
+
+import 'package:collection/collection.dart';
+import 'package:source_maps/source_maps.dart';
+
+/// An interface for parsed nodes from a YAML source tree.
+///
+/// [YamlMap]s and [YamlList]s implement this interface in addition to the
+/// normal [Map] and [List] interfaces, so any maps and lists will be
+/// [YamlNode]s regardless of how they're accessed.
+///
+/// Scalars values like strings and numbers, on the other hand, don't have this
+/// interface by default. Instead, they can be accessed as [YamlScalar]s via
+/// [YamlMap.nodes] or [YamlList.nodes].
+abstract class YamlNode {
+  /// The source span for this node.
+  ///
+  /// [Span.getLocationMessage] can be used to produce a human-friendly message
+  /// about this node.
+  Span get span;
+
+  /// The inner value of this node.
+  ///
+  /// For [YamlScalar]s, this will return the wrapped value. For [YamlMap] and
+  /// [YamlList], it will return [this], since they already implement [Map] and
+  /// [List], respectively.
+  get value;
+}
+
+/// A read-only [Map] parsed from YAML.
+class YamlMap extends YamlNode with collection.MapMixin, UnmodifiableMapMixin  {
+  final Span span;
+
+  final Map<dynamic, YamlNode> nodes;
+
+  Map get value => this;
+
+  Iterable get keys => nodes.keys.map((node) => node.value);
+
+  /// Users of the library should not construct [YamlMap]s manually.
+  YamlMap(Map<dynamic, YamlNode> nodes, this.span)
+      : nodes = new UnmodifiableMapView<dynamic, YamlNode>(nodes);
+
+  operator [](key) {
+    var node = nodes[key];
+    return node == null ? null : node.value;
+  }
+}
+
+// TODO(nweiz): Use UnmodifiableListMixin when issue 18970 is fixed.
+/// A read-only [List] parsed from YAML.
+class YamlList extends YamlNode with collection.ListMixin {
+  final Span span;
+
+  final List<YamlNode> nodes;
+
+  List get value => this;
+
+  int get length => nodes.length;
+
+  set length(int index) {
+    throw new UnsupportedError("Cannot modify an unmodifiable List");
+  }
+
+  /// Users of the library should not construct [YamlList]s manually.
+  YamlList(List<YamlNode> nodes, this.span)
+      : nodes = new UnmodifiableListView<YamlNode>(nodes);
+
+  operator [](int index) => nodes[index].value;
+
+  operator []=(int index, value) {
+    throw new UnsupportedError("Cannot modify an unmodifiable List");
+  }
+}
+
+/// A wrapped scalar value parsed from YAML.
+class YamlScalar extends YamlNode {
+  final Span span;
+
+  final value;
+
+  /// Users of the library should not construct [YamlScalar]s manually.
+  YamlScalar(this.value, this.span);
+
+  String toString() => value.toString();
+}