Rewrite the pkg/yaml parser.

pkg/yaml/lib/src/loader.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.loader;
+
+import 'package:source_span/source_span.dart';
+
+import 'equality.dart';
+import 'event.dart';
+import 'parser.dart';
+import 'yaml_document.dart';
+import 'yaml_exception.dart';
+import 'yaml_node.dart';
+
+/// A loader that reads [Event]s emitted by a [Parser] and emits
+/// [YamlDocument]s.
+///
+/// This is based on the libyaml loader, available at
+/// https://github.com/yaml/libyaml/blob/master/src/loader.c. The license for
+/// that is available in ../../libyaml-license.txt.
+class Loader {
+  /// The underlying [Parser] that generates [Event]s.
+  final Parser _parser;
+
+  /// Aliases by the alias name.
+  final _aliases = new Map<String, YamlNode>();
+
+  /// The span of the entire stream emitted so far.
+  FileSpan get span => _span;
+  FileSpan _span;
+
+  /// Creates a loader that loads [source].
+  ///
+  /// [sourceUrl] can be a String or a [Uri].
+  Loader(String source, {sourceUrl})
+      : _parser = new Parser(source, sourceUrl: sourceUrl) {
+    var event = _parser.parse();
+    _span = event.span;
+    assert(event.type == EventType.STREAM_START);
+  }
+
+  /// Loads the next document from the stream.
+  ///
+  /// If there are no more documents, returns `null`.
+  YamlDocument load() {
+    if (_parser.isDone) return null;
+
+    var event = _parser.parse();
+    if (event.type == EventType.STREAM_END) {
+      _span = _span.expand(event.span);
+      return null;
+    }
+
+    var document = _loadDocument(event);
+    _span = _span.expand(document.span);
+    _aliases.clear();
+    return document;
+  }
+
+  /// Composes a document object.
+  YamlDocument _loadDocument(DocumentStartEvent firstEvent) {
+    var contents = _loadNode(_parser.parse());
+
+    var lastEvent = _parser.parse();
+    assert(lastEvent.type == EventType.DOCUMENT_END);
+
+    return new YamlDocument.internal(
+        contents,
+        firstEvent.span.expand(lastEvent.span),
+        firstEvent.versionDirective,
+        firstEvent.tagDirectives,
+        startImplicit: firstEvent.isImplicit,
+        endImplicit: lastEvent.isImplicit);
+  }
+
+  /// Composes a node.
+  YamlNode _loadNode(Event firstEvent) {
+    switch (firstEvent.type) {
+      case EventType.ALIAS: return _loadAlias(firstEvent);
+      case EventType.SCALAR: return _loadScalar(firstEvent);
+      case EventType.SEQUENCE_START: return _loadSequence(firstEvent);
+      case EventType.MAPPING_START: return _loadMapping(firstEvent);
+      default: throw "Unreachable";
+    }
+  }
+
+  /// Registers an anchor.
+  void _registerAnchor(String anchor, YamlNode node) {
+    if (anchor == null) return;
+
+    // libyaml throws an error for duplicate anchors, but example 7.1 makes it
+    // clear that they should be overridden:
+    // http://yaml.org/spec/1.2/spec.html#id2786448.
+
+    _aliases[anchor] = node;
+  }
+
+  /// Composes a node corresponding to an alias.
+  YamlNode _loadAlias(AliasEvent event) {
+    var alias = _aliases[event.name];
+    if (alias != null) return alias;
+
+    throw new YamlException("Undefined alias.", event.span);
+  }
+
+  /// Composes a scalar node.
+  YamlNode _loadScalar(ScalarEvent scalar) {
+    var node;
+    if (scalar.tag == "!") {
+      node = _parseString(scalar);
+    } else if (scalar.tag != null) {
+      node = _parseByTag(scalar);
+    } else {
+      node = _parseNull(scalar);
+      if (node == null) node = _parseBool(scalar);
+      if (node == null) node = _parseInt(scalar);
+      if (node == null) node = _parseFloat(scalar);
+      if (node == null) node = _parseString(scalar);
+    }
+
+    _registerAnchor(scalar.anchor, node);
+    return node;
+  }
+
+  /// Composes a sequence node.
+  YamlNode _loadSequence(SequenceStartEvent firstEvent) {
+    if (firstEvent.tag != "!" && firstEvent.tag != null &&
+        firstEvent.tag != "tag:yaml.org,2002:seq") {
+      throw new YamlException("Invalid tag for sequence.", firstEvent.span);
+    }
+
+    var children = [];
+    var node = new YamlList.internal(
+        children, firstEvent.span, firstEvent.style);
+    _registerAnchor(firstEvent.anchor, node);
+
+    var event = _parser.parse();
+    while (event.type != EventType.SEQUENCE_END) {
+      children.add(_loadNode(event));
+      event = _parser.parse();
+    }
+
+    setSpan(node, firstEvent.span.expand(event.span));
+    return node;
+  }
+
+  /// Composes a mapping node.
+  YamlNode _loadMapping(MappingStartEvent firstEvent) {
+    if (firstEvent.tag != "!" && firstEvent.tag != null &&
+        firstEvent.tag != "tag:yaml.org,2002:map") {
+      throw new YamlException("Invalid tag for mapping.", firstEvent.span);
+    }
+
+    var children = deepEqualsMap();
+    var node = new YamlMap.internal(
+        children, firstEvent.span, firstEvent.style);
+    _registerAnchor(firstEvent.anchor, node);
+
+    var event = _parser.parse();
+    while (event.type != EventType.MAPPING_END) {
+      var key = _loadNode(event);
+      var value = _loadNode(_parser.parse());
+      children[key] = value;
+      event = _parser.parse();
+    }
+
+    setSpan(node, firstEvent.span.expand(event.span));
+    return node;
+  }
+
+  /// Parses a scalar according to its tag name.
+  YamlScalar _parseByTag(ScalarEvent scalar) {
+    switch (scalar.tag) {
+      case "tag:yaml.org,2002:null": return _parseNull(scalar);
+      case "tag:yaml.org,2002:bool": return _parseBool(scalar);
+      case "tag:yaml.org,2002:int": return _parseInt(scalar);
+      case "tag:yaml.org,2002:float": return _parseFloat(scalar);
+      case "tag:yaml.org,2002:str": return _parseString(scalar);
+    }
+    throw new YamlException('Undefined tag: ${scalar.tag}.', scalar.span);
+  }
+
+  /// Parses a null scalar.
+  YamlScalar _parseNull(ScalarEvent scalar) {
+    // TODO(nweiz): stop using regexps.
+    // TODO(nweiz): add ScalarStyle and implicit metadata to the scalars.
+    if (new RegExp(r"^(null|Null|NULL|~|)$").hasMatch(scalar.value)) {
+      return new YamlScalar.internal(null, scalar.span, scalar.style);
+    } else {
+      return null;
+    }
+  }
+
+  /// Parses a boolean scalar.
+  YamlScalar _parseBool(ScalarEvent scalar) {
+    var match = new RegExp(r"^(?:(true|True|TRUE)|(false|False|FALSE))$").
+        firstMatch(scalar.value);
+    if (match == null) return null;
+    return new YamlScalar.internal(
+        match.group(1) != null, scalar.span, scalar.style);
+  }
+
+  /// Parses an integer scalar.
+  YamlScalar _parseInt(ScalarEvent scalar) {
+    var match = new RegExp(r"^[-+]?[0-9]+$").firstMatch(scalar.value);
+    if (match != null) {
+      return new YamlScalar.internal(
+          int.parse(match.group(0)), scalar.span, scalar.style);
+    }
+
+    match = new RegExp(r"^0o([0-7]+)$").firstMatch(scalar.value);
+    if (match != null) {
+      var n = int.parse(match.group(1), radix: 8);
+      return new YamlScalar.internal(n, scalar.span, scalar.style);
+    }
+
+    match = new RegExp(r"^0x[0-9a-fA-F]+$").firstMatch(scalar.value);
+    if (match != null) {
+      return new YamlScalar.internal(
+          int.parse(match.group(0)), scalar.span, scalar.style);
+    }
+
+    return null;
+  }
+
+  /// Parses a floating-point scalar.
+  YamlScalar _parseFloat(ScalarEvent scalar) {
+    var match = new RegExp(
+          r"^[-+]?(\.[0-9]+|[0-9]+(\.[0-9]*)?)([eE][-+]?[0-9]+)?$").
+        firstMatch(scalar.value);
+    if (match != null) {
+      // YAML allows floats of the form "0.", but Dart does not. Fix up those
+      // floats by removing the trailing dot.
+      var matchStr = match.group(0).replaceAll(new RegExp(r"\.$"), "");
+      return new YamlScalar.internal(
+          double.parse(matchStr), scalar.span, scalar.style);
+    }
+
+    match = new RegExp(r"^([+-]?)\.(inf|Inf|INF)$").firstMatch(scalar.value);
+    if (match != null) {
+      var value = match.group(1) == "-" ? -double.INFINITY : double.INFINITY;
+      return new YamlScalar.internal(value, scalar.span, scalar.style);
+    }
+
+    match = new RegExp(r"^\.(nan|NaN|NAN)$").firstMatch(scalar.value);
+    if (match != null) {
+      return new YamlScalar.internal(double.NAN, scalar.span, scalar.style);
+    }
+
+    return null;
+  }
+
+  /// Parses a string scalar.
+  YamlScalar _parseString(ScalarEvent scalar) =>
+      new YamlScalar.internal(scalar.value, scalar.span, scalar.style);
+}