discard code completion cache if context or other sources change

pkg/analysis_server/lib/src/domain_completion.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 domain.completion;
 
+import 'dart:async';
+
 import 'package:analysis_server/src/analysis_server.dart';
 import 'package:analysis_server/src/constants.dart';
 import 'package:analysis_server/src/protocol.dart';
 import 'package:analysis_server/src/services/completion/completion_manager.dart';
+import 'package:analysis_server/src/services/search/search_engine.dart';
+import 'package:analyzer/src/generated/engine.dart';
+import 'package:analyzer/src/generated/source.dart';
 
 export 'package:analysis_server/src/services/completion/completion_manager.dart'
     show CompletionPerformance, OperationPerformance;
 
 /**
  * Instances of the class [CompletionDomainHandler] implement a [RequestHandler]
  * that handles requests in the search domain.
  */
 class CompletionDomainHandler implements RequestHandler {
   /**
    * The analysis server that is using this handler to process requests.
    */
   final AnalysisServer server;
 
   /**
    * The next completion response id.
    */
   int _nextCompletionId = 0;
 
   /**
    * Cached information from a prior completion operation.
    * The type of cached information depends upon the completion operation.
    */
-  // TODO (danrubel) clear cache if either source or context changes
   CompletionCache _cache;
 
   /**
+   * The subscription for the cached context's source change stream.
+   */
+  StreamSubscription<SourcesChangedEvent> _sourcesChangedSubscription;
+
+  /**
    * Code completion peformance for the last completion operation.
    */
   CompletionPerformance performance;
 
   /**
    * Initialize a new request handler for the given [server].
    */
-  CompletionDomainHandler(this.server);
+  CompletionDomainHandler(this.server) {
+    server.onContextsChanged.listen(contextsChanged);
+  }
+
+  /**
+   * If the context associated with the cache has changed or been removed
+   * then discard the cache.
+   */
+  void contextsChanged(ContextsChangedEvent event) {
+    if (_cache != null) {
+      AnalysisContext context = _cache.context;
+      if (event.changed.contains(context) || event.removed.contains(context)) {
+        _discardCache();
+      }
+    }
+  }
+
+  CompletionManager createCompletionManager(AnalysisContext context,
+      Source source, int offset, SearchEngine searchEngine, CompletionCache cache,
+      CompletionPerformance performance) {
+    return new CompletionManager.create(
+        context,
+        source,
+        offset,
+        searchEngine,
+        cache,
+        performance);
+  }
 
   @override
   Response handleRequest(Request request) {
     try {
       String requestName = request.method;
       if (requestName == COMPLETION_GET_SUGGESTIONS) {
         return processRequest(request);
       }
     } on RequestFailure catch (exception) {
       return exception.response;
     }
     return null;
   }
 
   /**
    * Process a `completion.getSuggestions` request.
    */
   Response processRequest(Request request) {
     performance = new CompletionPerformance();
     // extract params
     CompletionGetSuggestionsParams params =
         new CompletionGetSuggestionsParams.fromRequest(request);
     // schedule completion analysis
     String completionId = (_nextCompletionId++).toString();
-    CompletionManager manager = new CompletionManager.create(
+    CompletionManager manager = createCompletionManager(
         server.getAnalysisContext(params.file),
         server.getSource(params.file),
         params.offset,
         server.searchEngine,
         _cache,
         performance);
     manager.results().listen((CompletionResult result) {
       sendCompletionNotification(
           completionId,
           result.replacementOffset,
           result.replacementLength,
           result.suggestions,
           result.last);
       if (result.last) {
         performance.complete();
-        _cache = manager.completionCache;
+        CompletionCache newCache = manager.completionCache;
+        if (_cache != newCache) {
+          if (_cache != null) {
+            _discardCache();
+          }
+          _cache = newCache;
+          if (_cache.context != null) {
+            _sourcesChangedSubscription =
+                _cache.context.onSourcesChanged.listen(sourcesChanged);
+          }
+        }
       }
     });
     // initial response without results
     return new CompletionGetSuggestionsResult(
         completionId).toResponse(request.id);
   }
 
   /**
    * Send completion notification results.
    */
   void sendCompletionNotification(String completionId, int replacementOffset,
       int replacementLength, Iterable<CompletionSuggestion> results, bool isLast) {
     server.sendNotification(
         new CompletionResultsParams(
             completionId,
             replacementOffset,
             replacementLength,
             results,
             isLast).toNotification());
   }
+
+  /**
+   * Discard the cache if a source other than the source referenced by
+   * the cache changes or if any source is added, removed, or deleted.
+   */
+  void sourcesChanged(SourcesChangedEvent event) {
+
+    bool shouldDiscardCache(SourcesChangedEvent event) {
+      if (_cache == null) {
+        return false;
+      }
+      if (event.wereSourcesAdded || event.wereSourcesRemovedOrDeleted) {
+        return true;
+      }
+      var changedSources = event.changedSources;
+      return changedSources.length > 2 ||
+          (changedSources.length == 1 && !changedSources.contains(_cache.source));
+    }
+
+    if (shouldDiscardCache(event)) {
+      _discardCache();
+    }
+  }
+
+  /**
+   * Discard the sourcesChanged subscription if any
+   */
+  void _discardCache() {
+    if (_sourcesChangedSubscription != null) {
+      _sourcesChangedSubscription.cancel();
+      _sourcesChangedSubscription = null;
+    }
+    _cache = null;
+  }
 }