Use an interning table to compare and hash FileBasedSource objects.

pkg/analyzer/lib/src/generated/source_io.dart

 // Copyright (c) 2014, 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.
 
 // This code was auto-generated, is not intended to be edited, and is subject to
 // significant change. Please see the README file for more information.
 
 library engine.source.io;
 
+import 'dart:collection';
+
 import 'engine.dart';
 import 'java_core.dart';
 import 'java_engine.dart';
 import 'java_io.dart';
 import 'source.dart';
 import 'utilities_general.dart';
 
 export 'source.dart';
 
 /**
@@ skipping 66 matching lines @@
 /**
  * Instances of the class `FileBasedSource` implement a source that represents a file.
  */
 class FileBasedSource extends Source {
   /**
    * A function that changes the way that files are read off of disk.
    */
   static Function fileReadMode = (String s) => s;
 
   /**
+   * Map from encoded URI/filepath pair to a unique integer identifier.  This
+   * identifier is used for equality tests and hash codes.
+   *
+   * The URI and filepath are joined into a pair by separating them with an '@'
+   * character.
+   */
+  static final Map<String, int> _idTable = new HashMap<String, int>();
+
+  /**
    * The URI from which this source was originally derived.
    */
   final Uri uri;
 
   /**
+   * The unique ID associated with this [FileBasedSource].
+   */
+  final int id;
+
+  /**
    * The file represented by this source.
    */
   final JavaFile file;
 
   /**
    * The cached absolute path of this source.
    */
   String _absolutePath;
 
   /**
    * The cached encoding for this source.
    */
   String _encoding;
 
   /**
    * Initialize a newly created source object.
    *
    * @param file the file represented by this source
    */
   FileBasedSource.con1(JavaFile file) : this.con2(file.toURI(), file);
 
   /**
    * Initialize a newly created source object.
    *
    * @param file the file represented by this source
    * @param uri the URI from which this source was originally derived
    */
-  FileBasedSource.con2(this.uri, this.file);
+  FileBasedSource.con2(Uri uri, JavaFile file)
+      : uri = uri, file = file,
+        id = _idTable.putIfAbsent(
+          '$uri@${file.getPath()}',
+          () => _idTable.length);
 
   @override
   TimestampedData<String> get contents {
     return PerformanceStatistics.io.makeCurrentWhile(() {
       return contentsFromFile;
     });
   }
 
   /**
    * Get the contents and timestamp of the underlying file.
@@ skipping 22 matching lines @@
 
   @override
   String get fullName {
     if (_absolutePath == null) {
       _absolutePath = file.getAbsolutePath();
     }
     return _absolutePath;
   }
 
   @override
-  int get hashCode => file.hashCode;
+  int get hashCode => id;
 
   @override
   bool get isInSystemLibrary => uri.scheme == DartUriResolver.DART_SCHEME;
 
   @override
   int get modificationStamp => file.lastModified();
 
   @override
   String get shortName => file.getName();
 
   @override
   UriKind get uriKind {
     String scheme = uri.scheme;
     if (scheme == PackageUriResolver.PACKAGE_SCHEME) {
       return UriKind.PACKAGE_URI;
     } else if (scheme == DartUriResolver.DART_SCHEME) {
       return UriKind.DART_URI;
     } else if (scheme == FileUriResolver.FILE_SCHEME) {
       return UriKind.FILE_URI;
     }
     return UriKind.FILE_URI;
   }
 
   @override
   bool operator ==(Object object) =>
-      object is FileBasedSource && uri == object.uri;
+      object is FileBasedSource && id == object.id;
 
   @override
   bool exists() => file.isFile();
 
   @override
   Uri resolveRelativeUri(Uri containedUri) {
     try {
       Uri baseUri = uri;
       bool isOpaque = uri.isAbsolute && !uri.path.startsWith('/');
       if (isOpaque) {
@@ skipping 310 matching lines @@
   }
 
   /**
    * Return `true` if the given URI is a `file` URI.
    *
    * @param uri the URI being tested
    * @return `true` if the given URI is a `file` URI
    */
   static bool isFileUri(Uri uri) => uri.scheme == FILE_SCHEME;
 }