Handle SDK extensions in the SDK

pkg/analyzer/lib/source/sdk_ext.dart

 // Copyright (c) 2015, 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.
 
 library analyzer.source.sdk_ext;
 
 import 'dart:convert';
 import 'dart:core' hide Resource;
 
 import 'package:analyzer/file_system/file_system.dart';
@@ skipping 13 matching lines @@
 ///   "dart:sky": "../sdk_ext/dart_sky.dart"
 /// }
 ///
 /// If a key doesn't begin with `dart:` it is ignored.
 class SdkExtUriResolver extends UriResolver {
   static const String SDK_EXT_NAME = '_sdkext';
   static const String DART_COLON_PREFIX = 'dart:';
 
   final Map<String, String> _urlMappings = <String, String>{};
 
+  /**
+   * The absolute paths of the extension files that contributed to the
+   * [_urlMappings].
+   */
+  final List<String> extensionFilePaths = <String>[];
+
   /// Construct a [SdkExtUriResolver] from a package map
   /// (see [PackageMapProvider]).
   SdkExtUriResolver(Map<String, List<Folder>> packageMap) {
     if (packageMap == null) {
       return;
     }
     packageMap.forEach(_processPackage);
   }
 
   /// Number of sdk extensions.
@@ skipping 96 matching lines @@
   void _processSdkExt(String sdkExtJSON, Folder libDir) {
     var sdkExt;
     try {
       sdkExt = JSON.decode(sdkExtJSON);
     } catch (e) {
       return;
     }
     if ((sdkExt == null) || (sdkExt is! Map)) {
       return;
     }
-    sdkExt.forEach((k, v) => _processSdkExtension(k, v, libDir));
+    bool contributed = false;
+    sdkExt.forEach((k, v) {
+      if (_processSdkExtension(k, v, libDir)) {
+        contributed = true;
+      }
+    });
+    if (contributed) {
+      extensionFilePaths.add(libDir.getChild(SDK_EXT_NAME).path);
+    }
   }
 
   /// Install the mapping from [name] to [libDir]/[file].
-  void _processSdkExtension(String name, String file, Folder libDir) {
+  bool _processSdkExtension(String name, String file, Folder libDir) {
     if (!name.startsWith(DART_COLON_PREFIX)) {
       // SDK extensions must begin with 'dart:'.
-      return;
+      return false;
     }
     var key = name;
     var value = libDir.canonicalizePath(file);
     _urlMappings[key] = value;
+    return true;
   }
 
   /// Read the contents of [libDir]/[SDK_EXT_NAME] as a string.
   /// Returns null if the file doesn't exist.
   String _readDotSdkExt(Folder libDir) {
     File file = libDir.getChild(SDK_EXT_NAME);
     try {
       return file.readAsStringSync();
     } on FileSystemException {
       // File can't be read.
@@ skipping 11 matching lines @@
   /// Resolve a 'part' statement inside an sdk extension.
   Source _resolvePart(Uri libraryEntry, String partPath, Uri importUri) {
     // Library part.
     var directory = pathos.dirname(libraryEntry.path);
     var partUri = new Uri.file(pathos.join(directory, partPath));
     assert(partUri.isAbsolute);
     JavaFile javaFile = new JavaFile.fromUri(partUri);
     return new FileBasedSource(javaFile, importUri);
   }
 }