Clean up hacky handling of "dart:" URIs in 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>{};
+  final _uriToIndexMap = <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() {
@@ skipping 17 matching lines @@
   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);
+  /// If [allocate] is `false` (the default), the uri must have previously been
+  /// allocated a corresponding path, e.g. via a call to [store].  If [allocate]
+  /// is `true`, then a new path will be allocated if necessary.
+  String pathForUri(Uri uri, {bool allocate: false}) {
+    return _pathForIndex(_indexForUri(uri, allocate));
   }
 
   /// 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;
-    }
+    int index = _indexForUri(uri, true);
+    _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));
   }
 
+  int _indexForUri(Uri uri, bool allocate) {
+    int index = _uriToIndexMap[uri];
+    assert(allocate || index != null);
+    if (index == null) {
+      index = _uris.length;
+      _uris.add(uri);
+      _uriToIndexMap[uri] = index;
+      _contents.add(null);
+    }
+    return index;
+  }
+
   /// Return the arbitrary path associated with the given index.
   String _pathForIndex(int index) => '/$index.dart';
 }