Add a basic YAML processor. Much of the language is still unimplemented.

utils/yaml/model.dart

Index: utils/yaml/model.dart
diff --git a/utils/yaml/model.dart b/utils/yaml/model.dart
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+// 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.
+
+// This file contains the node classes for the internal representations of YAML
+// documents. These nodes are used for both the serialization tree and the
+// representation graph.
+
+/** A tag that indicates the type of a YAML node. */
+class _Tag implements Hashable {
+  // TODO(nweiz): it would better match the semantics of the spec if there were
+  // a singleton instance of this class for each tag.
+
+  static final SCALAR_KIND = 0;
+  static final SEQUENCE_KIND = 1;
+  static final MAPPING_KIND = 2;
+
+  static final String YAML_URI_PREFIX = 'tag:yaml.org,2002:';
+
+  /** The name of the tag, either a URI or a local tag beginning with "!". */
+  final String name;
+
+  /** The kind of the tag: SCALAR_KIND, SEQUENCE_KIND, or MAPPING_KIND. */
+  final int kind;
+
+  _Tag(this.name, this.kind);
+
+  _Tag.scalar(String name) : this(name, SCALAR_KIND);
+  _Tag.sequence(String name) : this(name, SEQUENCE_KIND);
+  _Tag.mapping(String name) : this(name, MAPPING_KIND);
+
+  /** Returns the standard YAML tag URI for [type]. */
+  static String yaml(String type) => "tag:yaml.org,2002:$type";
+
+  /** Two tags are equal if their URIs are equal. */
+  operator ==(other) {
+    if (other is! _Tag) return false;
+    return name == other.name;
+  }
+
+  String toString() {
+    if (name.startsWith(YAML_URI_PREFIX)) {
+      return '!!${name.substring(YAML_URI_PREFIX.length)}';
+    } else {
+      return '!<$name>';
+    }
+  }
+
+  int hashCode() => name.hashCode();
+}
+
+/** The abstract class for YAML nodes. */
+class _Node implements Hashable {
+  /** Every YAML node has a tag that describes its type. */
+  _Tag tag;
+
+  /** Any YAML node can have an anchor associated with it. */
+  String anchor;
+
+  _Node(this.tag, [this.anchor]);
+
+  bool operator ==(other) {
+    if (other is! _Node) return false;
+    return tag == other.tag;
+  }
+
+  int hashCode() => _hashCode([tag, anchor]);
+
+  abstract visit(_Visitor v);
+}
+
+/** A sequence node represents an ordered list of nodes. */
+class _SequenceNode extends _Node {
+  /** The nodes in the sequence. */
+  List<_Node> content;
+
+  _SequenceNode(String tagName, this.content)
+    : super(new _Tag.sequence(tagName));
+
+  /** Two sequences are equal if their tags and contents are equal. */
+  bool operator ==(other) {
+    // Should be super != other; bug 2554
+    if (!(super == other) || other is! _SequenceNode) return false;
+    if (content.length != other.content.length) return false;
+    for (var i = 0; i < content.length; i++) {
+      if (content[i] != other.content[i]) return false;
+    }
+    return true;
+  }
+
+  String toString() => '$tag [${Strings.join(content.map((e) => '$e'), ', ')}]';
+
+  int hashCode() => super.hashCode() ^ _hashCode(content);
+
+  visit(_Visitor v) => v.visitSequence(this);
+}
+
+/** An alias node is a reference to an anchor. */
+class _AliasNode extends _Node {
+  _AliasNode(String anchor) : super(new _Tag.scalar(_Tag.yaml("str")), anchor);
+
+  visit(_Visitor v) => v.visitAlias(this);
+}
+
+/** A scalar node represents all YAML nodes that have a single value. */
+class _ScalarNode extends _Node {
+  /** The string value of the scalar node, if it was created by the parser. */
+  final String _content;
+
+  /** The Dart value of the scalar node, if it was created by the composer. */
+  final value;
+
+  /**
+   * Creates a new Scalar node.
+   *
+   * Exactly one of [content] and [value] should be specified. Content should be
+   * specified for a newly-parsed scalar that hasn't yet been composed. Value
+   * should be specified for a composed scalar, although `null` is a valid
+   * value.
+   */
+  _ScalarNode(String tagName, [String content, this.value])
+   : _content = content,
+     super(new _Tag.scalar(tagName));
+
+  /** Two scalars are equal if their string representations are equal. */
+  bool operator ==(other) {
+    // Should be super != other; bug 2554
+    if (!(super == other) || other is! _ScalarNode) return false;
+    return content == other.content;
+  }
+
+  /**
+   * Returns the string representation of the scalar. After composition, this is
+   * equal to the canonical serialization of the value of the scalar.
+   */
+  String get content() => _content != null ? _content : canonicalContent;
+
+  /**
+   * Returns the canonical serialization of the value of the scalar. If the
+   * value isn't given, the result of this will be "null".
+   */
+  String get canonicalContent() {
+    if (value == null || value is bool || value is int) return '$value';
+
+    if (value is num) {
+      // 20 is the maximum value for this argument, which we use since YAML
+      // doesn't specify a maximum.
+      return value.toStringAsExponential(20).
+        replaceFirst(const RegExp("0+e"), "e");
+    }
+
+    if (value is String) {
+      // TODO(nweiz): This could be faster if we used a RegExp to check for
+      // special characters and short-circuited if they didn't exist.
+
+      var escapedValue = value.charCodes().map((c) {
+        switch (c) {
+        case _Parser.TAB: return "\\t";
+        case _Parser.LF: return "\\n";
+        case _Parser.CR: return "\\r";
+        case _Parser.DOUBLE_QUOTE: return '\\"';
+        case _Parser.NULL: return "\\0";
+        case _Parser.BELL: return "\\a";
+        case _Parser.BACKSPACE: return "\\b";
+        case _Parser.VERTICAL_TAB: return "\\v";
+        case _Parser.FORM_FEED: return "\\f";
+        case _Parser.ESCAPE: return "\\e";
+        case _Parser.BACKSLASH: return "\\\\";
+        case _Parser.NEL: return "\\N";
+        case _Parser.NBSP: return "\\_";
+        case _Parser.LINE_SEPARATOR: return "\\L";
+        case _Parser.PARAGRAPH_SEPARATOR: return "\\P";
+        default:
+          if (c < 0x20 || (c >= 0x7f && c < 0x100)) {
+            return "\\x${zeroPad(c.toRadixString(16).toUpperCase(), 2)}";
+          } else if (c >= 0x100 && c < 0x10000) {
+            return "\\u${zeroPad(c.toRadixString(16).toUpperCase(), 4)}";
+          } else if (c >= 0x10000) {
+            return "\\u${zeroPad(c.toRadixString(16).toUpperCase(), 8)}";
+          } else {
+            return new String.fromCharCodes([c]);
+          }
+        }
+      });
+      return '"${Strings.join(escapedValue, '')}"';
+    }
+
+    throw new Error("unknown scalar value: $value");
+  }
+
+  String toString() => '$tag "$content"';
+
+  /**
+   * Left-pads [str] with zeros so that it's at least [length] characters
+   * long.
+   */
+  String zeroPad(String str, int length) {
+    assert(length >= str.length);
+    var prefix = [];
+    prefix.insertRange(0, length - str.length, '0');
+    return '${Strings.join(prefix, '')}$str';
+  }
+
+  int hashCode() => super.hashCode() ^ content.hashCode();
+
+  visit(_Visitor v) => v.visitScalar(this);
+}
+
+/** A mapping node represents an unordered map of nodes to nodes. */
+class _MappingNode extends _Node {
+  /** The node map. */
+  Map<_Node, _Node> content;
+
+  _MappingNode(String tagName, this.content)
+    : super(new _Tag.mapping(tagName));
+
+  /** Two mappings are equal if their tags and contents are equal. */
+  bool operator ==(other) {
+    // Should be super != other; bug 2554
+    if (!(super == other) || other is! _MappingNode) return false;
+    if (content.length != other.content.length) return false;
+    for (var key in content.getKeys()) {
+      if (!other.content.containsKey(key)) return false;
+      if (content[key] != other.content[key]) return false;
+    }
+    return true;
+  }
+
+  String toString() {
+    var strContent = Strings.join(content.getKeys().
+        map((k) => '${k}: ${content[k]}'), ', ');
+    return '$tag {$strContent}';
+  }
+
+  int hashCode() => super.hashCode() ^ _hashCode(content);
+
+  visit(_Visitor v) => v.visitMapping(this);
+}