Cache transitive files in FileState.

pkg/front_end/lib/src/incremental/file_state.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.
 
 import 'dart:async';
 import 'dart:typed_data';
 
 import 'package:convert/convert.dart';
 import 'package:crypto/crypto.dart';
 import 'package:front_end/file_system.dart';
@@ skipping 31 matching lines @@
   bool _hasMixinApplication;
   List<int> _apiSignature;
 
   List<NamespaceExport> _exports;
   List<FileState> _importedLibraries;
   List<FileState> _exportedLibraries;
   List<FileState> _partFiles;
 
   Set<FileState> _directReferencedFiles = new Set<FileState>();
   List<FileState> _directReferencedLibraries = <FileState>[];
+  Set<FileState> _transitiveFiles;
 
   /// This flag is set to `true` during the mark phase of garbage collection
   /// and set back to `false` for survived instances.
   bool _gcMarked = false;
 
   FileState._(this._fsState, this.uri, this.fileUri);
 
   /// The MD5 signature of the file API as a byte array.
   /// It depends on all non-comment tokens outside the block bodies.
   List<int> get apiSignature => _apiSignature;
@@ skipping 37 matching lines @@
   /// Return topologically sorted cycles of dependencies for this library.
   List<LibraryCycle> get topologicalOrder {
     var libraryWalker = new _LibraryWalker();
     libraryWalker.walk(libraryWalker.getNode(this));
     return libraryWalker.topologicallySortedCycles;
   }
 
   /// Return the set of transitive files - the file itself and all of the
   /// directly or indirectly referenced files.
   Set<FileState> get transitiveFiles {
-    // TODO(scheglov) add caching.
-    var transitiveFiles = new Set<FileState>();
+    if (_transitiveFiles == null) {
+      _transitiveFiles = new Set<FileState>();
 
-    void appendReferenced(FileState file) {
-      if (transitiveFiles.add(file)) {
-        file._directReferencedFiles.forEach(appendReferenced);
+      void appendReferenced(FileState file) {
+        if (_transitiveFiles.add(file)) {
+          file._directReferencedFiles.forEach(appendReferenced);
+        }
       }
+
+      appendReferenced(this);
     }
-
-    appendReferenced(this);
-    return transitiveFiles;
+    return _transitiveFiles;
   }
 
   @override
   bool operator ==(Object other) {
     return other is FileState && other.uri == uri;
   }
 
   /// Read the file content and ensure that all of the file properties are
   /// consistent with the read content, including all its dependencies.
   Future<Null> refresh() async {
@@ skipping 54 matching lines @@
       }
     }
     for (var part_ in unlinkedUnit.parts) {
       FileState file = await _getFileForRelativeUri(part_);
       if (file != null) {
         _partFiles.add(file);
       }
     }
 
     // Compute referenced files.
+    var oldDirectReferencedFiles = _directReferencedFiles;
     _directReferencedFiles = new Set<FileState>()
       ..addAll(_importedLibraries)
       ..addAll(_exportedLibraries)
       ..addAll(_partFiles);
     _directReferencedLibraries = (new Set<FileState>()
           ..addAll(_importedLibraries)
           ..addAll(_exportedLibraries))
         .toList();
+
+    // If the set of directly referenced files of this file is changed,
+    // then the transitive sets of files that include this file are also
+    // changed. Reset these transitive sets.
+    if (_directReferencedFiles.length != oldDirectReferencedFiles.length ||
+        !_directReferencedFiles.containsAll(oldDirectReferencedFiles)) {
+      for (var file in _fsState._uriToFile.values) {
+        if (file._transitiveFiles != null &&
+            file._transitiveFiles.contains(this)) {
+          file._transitiveFiles = null;
+        }
+      }
+    }
   }
 
   @override
   String toString() {
     if (uri.scheme == 'file') return uri.path;
     return uri.toString();
   }
 
   /// Fasta unconditionally loads all VM libraries.  In order to be able to
   /// serve them using the file system view, pretend that all of them were
@@ skipping 281 matching lines @@
       cycle.libraries.add(node.file);
       fileToCycleMap[node.file] = cycle;
     }
     topologicallySortedCycles.add(cycle);
   }
 
   _LibraryNode getNode(FileState file) {
     return nodesOfFiles.putIfAbsent(file, () => new _LibraryNode(this, file));
   }
 }