Store a file state in the incremental resolved AST generator.

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

 // 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>[];
 
+  /// Clear any contents stored in the file repository.  The association between
+  /// URI and arbitrary path is preserved.
+  ///
+  /// Subsequent calls to [contentsForPath] will have undefined results until
+  /// new contents are stored using [store].
+  void clearContents() {
+    for (var i = 0; i < _contents.length; i++) {
+      _contents[i] = null;
+    }
+  }
+
   /// 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)];
+  String contentsForPath(String path) {
+    var contents = _contents[_indexForPath(path)];
+    assert(contents != null);
+    return contents;
+  }
+
+  /// For testing purposes, return the contents of all files stored in the file
+  /// repository, as a map from path to contents string.
+  Map<String, String> getContentsForTesting() {
+    var result = <String, String>{};
+    for (var i = 0; i < _contents.length; i++) {
+      if (_contents[i] != null) result[_pathForIndex(i)] = _contents[i];
+    }
+    return result;
+  }
 
   /// 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);
   }
 
@@ skipping 22 matching lines @@
   /// 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';
 }