Create a "file repository" data structure to help interface analyzer and front_end code.

pkg/front_end/lib/src/base/file_repository.dart

Index: pkg/front_end/lib/src/base/file_repository.dart
diff --git a/pkg/front_end/lib/src/base/file_repository.dart b/pkg/front_end/lib/src/base/file_repository.dart
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index 0000000000000000000000000000000000000000..5c55d86171c6c80e736b98ee63c24db8e42aa173
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+++ b/pkg/front_end/lib/src/base/file_repository.dart
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+// Copyright (c) 2017, 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.
+
+/// Data structure storing an association between URI and file contents.
+///
+/// Each URI is also associated with a unique arbitrary path ending in ".dart".
+/// This allows interfacing with analyzer code that expects to manipulate paths
+/// rather than URIs.
+class FileRepository {
+  /// Regular expression matching the arbitrary file paths generated by
+  /// [_pathForIndex].
+  static final _pathRegexp = new RegExp(r'^/[0-9]+\.dart$');
+
+  /// The URIs currently stored in the repository.
+  final _uris = <Uri>[];
+
+  /// Map from a URI to its index in [_uris].
+  final _indexForUri = <Uri, int>{};
+
+  /// The file contents associated with the URIs in [_uris].
+  final _contents = <String>[];
+
+  /// Return the contents of the file whose arbitary path is [path].
+  ///
+  /// The path must have been returned by a previous call to [store] or
+  /// [pathForUri].
+  String contentsForPath(String path) => _contents[_indexForPath(path)];
+
+  /// Return the arbitrary path associated with [uri].
+  ///
+  /// The uri must have previously been passed to [store].
+  String pathForUri(Uri uri) {
+    int index = _indexForUri[uri];
+    assert(index != null);
+    return _pathForIndex(index);
+  }
+
+  /// Associate the given [uri] with file [contents].
+  ///
+  /// The arbitrary path associated with the file is returned.
+  String store(Uri uri, String contents) {
+    int index = _indexForUri[uri];
+    if (index == null) {
+      index = _uris.length;
+      _uris.add(uri);
+      _indexForUri[uri] = index;
+      _contents.add(contents);
+    } else {
+      _contents[index] = contents;
+    }
+    return _pathForIndex(index);
+  }
+
+  /// Return the URI for the file whose arbitrary path is [path].
+  ///
+  /// The path must have been returned by a previous call to [store] or
+  /// [pathForUri].
+  Uri uriForPath(String path) => _uris[_indexForPath(path)];
+
+  /// Return the index into [_uris] and [_contents] matching the arbitrary path
+  /// [path].
+  int _indexForPath(String path) {
+    assert(_pathRegexp.hasMatch(path));
+    return int.parse(path.substring(1, path.length - 5));
+  }
+
+  /// Return the arbitrary path associated with the given index.
+  String _pathForIndex(int index) => '/$index.dart';
+}