Move source maps package to the dart repo, so it can be used by other internal

pkg/source_maps/lib/builder.dart

Index: pkg/source_maps/lib/builder.dart
diff --git a/pkg/source_maps/lib/builder.dart b/pkg/source_maps/lib/builder.dart
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index 0000000000000000000000000000000000000000..ad80fa00093184e3bea79adb2a30cd6417d688b7
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+++ b/pkg/source_maps/lib/builder.dart
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+// Copyright (c) 2013, 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.
+
+/// Contains a builder object useful for creating source maps programatically.
+library source_maps.builder;
+
+// TODO(sigmund): add a builder for multi-section mappings.
+
+import 'dart:json' as json;
+import 'dart:collection';
+
+import 'span.dart';
+import 'src/vlq.dart';
+
+/// Builds a source map given a set of mappings.
+class SourceMapBuilder {
+
+  final List<Entry> _entries = <Entry>[];
+
+  /// Indices associated with file urls that will be part of the source map. We
+  /// use a linked hash-map so that `_urls.keys[_urls[u]] == u`
+  final Map<String, int> _urls = new LinkedHashMap<String, int>();
+
+  /// Indices associated with identifiers that will be part of the source map.
+  /// We use a linked hash-map so that `_names.keys[_names[n]] == n`
+  final Map<String, int> _names = new LinkedHashMap<String, int>();
+
+  /// Adds an entry mapping the [targetOffset] to [source].
+  void addFromOffset(Location source,
+      SourceFile targetFile, int targetOffset, String identifier) {
+    if (targetFile == null) {
+      throw new ArgumentError('targetFile cannot be null');
+    }
+    _entries.add(new Entry(source,
+          new FileLocation(targetFile, targetOffset), identifier));
+  }
+
+  /// Adds an entry mapping [target] to [source].
+  void addSpan(Span source, Span target) {
+    var name = source.isIdentifier ? source.text : null;
+    _entries.add(new Entry(source.start, target.start, name));
+  }
+
+  void addLocation(Location source, Location target, String identifier) {
+    _entries.add(new Entry(source, target, identifier));
+  }
+
+  /// Encodes all mappings added to this builder as a json map.
+  Map build(String fileUrl) {
+    var buff = new StringBuffer();
+    var line = 0;
+    var column = 0;
+    var srcLine = 0;
+    var srcColumn = 0;
+    var srcUrlId = 0;
+    var srcNameId = 0;
+    var first = true;
+
+    // The encoding needs to be sorted by the target offsets.
+    _entries.sort();
+    for (var entry in _entries) {
+      int nextLine = entry.target.line;
+      if (nextLine > line) {
+        for (int i = line; i < nextLine; ++i) {
+          buff.write(';');
+        }
+        line = nextLine;
+        column = 0;
+        first = true;
+      }
+
+      if (!first) buff.write(',');
+      first = false;
+      column = _append(buff, column, entry.target.column);
+
+      if (entry.source == null) continue;
+
+      srcUrlId = _append(buff, srcUrlId,
+          _indexOf(_urls, entry.source.sourceUrl));
+      srcLine = _append(buff, srcLine, entry.source.line);
+      srcColumn = _append(buff, srcColumn, entry.source.column);
+
+      if (entry.identifierName == null) continue;
+      srcNameId = _append(buff, srcNameId,
+          _indexOf(_names, entry.identifierName));
+    }
+
+    var result = {
+      'version': 3,
+      'sourceRoot': '',
+      'sources': _urls.keys.toList(),
+      'names' : _names.keys.toList(),
+      'mappings' : buff.toString()
+    };
+    if (fileUrl != null) {
+      result['file'] = fileUrl;
+    }
+    return result;
+  }
+
+  /// Encodes all mappings added to this builder as a json string.
+  String toJson(String fileUrl) => json.stringify(build(fileUrl));
+
+  /// Get the index of [value] in [map], or create one if it doesn't exist.
+  int _indexOf(Map<String, int> map, String value) {
+    return map.putIfAbsent(value, () {
+      int index = map.length;
+      map[value] = index;
+      return index;
+    });
+  }
+
+  /// Appends to [buff] a VLQ encoding of [newValue] using the difference
+  /// between [oldValue] and [newValue]
+  static int _append(StringBuffer buff, int oldValue, int newValue) {
+    buff.writeAll(encodeVlq(newValue - oldValue));
+    return newValue;
+  }
+}
+
+/// An entry in the source map builder.
+class Entry implements Comparable {
+  /// Span denoting the original location in the input source file
+  final Location source;
+
+  /// Span indicating the corresponding location in the target file.
+  final Location target;
+
+  /// An identifier name, when this location is the start of an identifier.
+  final String identifierName;
+
+  Entry(this.source, this.target, this.identifierName);
+
+  /// Implements [Comparable] to ensure that entries are ordered by their
+  /// location in the target file. We sort primarily by the target offset
+  /// because source map files are encoded by printing each mapping in order as
+  /// they appear in the target file.
+  int compareTo(Entry other) {
+    int res = target.compareTo(other.target);
+    if (res != 0) return res;
+    res = source.sourceUrl.compareTo(other.source.sourceUrl);
+    if (res != 0) return res;
+    return source.compareTo(other.source);
+  }
+}