Issue 21506. Fix for adding back previously excluded resources in sub-folders.

pkg/analysis_server/lib/src/context_manager.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.
 
 library context.directory.manager;
 
 import 'dart:async';
 import 'dart:collection';
 
 import 'package:analyzer/file_system/file_system.dart';
@@ skipping 221 matching lines @@
    * Resursively adds all Dart and HTML files to the [changeSet].
    */
   void _addPreviouslyExcludedSources(_ContextInfo info, ChangeSet changeSet,
       Folder folder, List<String> oldExcludedPaths) {
     if (info.excludesResource(folder)) {
       return;
     }
     List<Resource> children = folder.getChildren();
     for (Resource child in children) {
       String path = child.path;
-      // ignore if wasn't previously excluded
-      bool wasExcluded =
-          _isExcludedBy(oldExcludedPaths, path) &&
-          !_isExcludedBy(excludedPaths, path);
-      if (!wasExcluded) {
-        continue;
-      }
       // add files, recurse into folders
       if (child is File) {
-        if (_shouldFileBeAnalyzed(child)) {
-          Source source = child.createSource();
-          changeSet.addedSource(source);
-          info.sources[path] = source;
+        // ignore if should not be analyzed at all
+        if (!_shouldFileBeAnalyzed(child)) {
+          continue;
         }
+        // ignore if was not excluded
+        bool wasExcluded =
+            _isExcludedBy(oldExcludedPaths, path) &&
+            !_isExcludedBy(excludedPaths, path);
+        if (!wasExcluded) {
+          continue;
+        }
+        // do add the file
+        Source source = child.createSource();
+        changeSet.addedSource(source);
+        info.sources[path] = source;
       } else if (child is Folder) {
         if (child.shortName == PACKAGES_NAME) {
           continue;
         }
         _addPreviouslyExcludedSources(info, changeSet, child, oldExcludedPaths);
       }
     }
   }
 
   /**
@@ skipping 381 matching lines @@
     return excludes(resource.path);
   }
 
   /**
    * Returns `true` if [path] is the pubspec file of this context.
    */
   bool isPubspec(String path) {
     return path == pubspecPath;
   }
 }