recompute package map when input file changes

pkg/analysis_server/lib/src/context_manager.dart

Index: pkg/analysis_server/lib/src/context_manager.dart
diff --git a/pkg/analysis_server/lib/src/context_manager.dart b/pkg/analysis_server/lib/src/context_manager.dart
index bfa8cb6fbd0c7fd383aefbde12a7d6ab2d3be71c..c4c7e1f71d0676af54689de14f06b54f66b35da4 100644
--- a/pkg/analysis_server/lib/src/context_manager.dart
+++ b/pkg/analysis_server/lib/src/context_manager.dart
@@ -387,11 +387,22 @@ abstract class ContextManager {
   }
 
   /**
+   * Cancel all dependency subscriptions for the given context.
+   */
+  void _cancelDependencySubscriptions(_ContextInfo info) {
+    for (StreamSubscription<WatchEvent> s in info.dependencySubscriptions) {
+      s.cancel();
+    }
+    info.dependencySubscriptions.clear();
+  }
+
+  /**
    * Compute the appropriate package URI resolver for [folder], and store
    * dependency information in [info]. Return `null` if no package map can
    * be computed.
    */
   UriResolver _computePackageUriResolver(Folder folder, _ContextInfo info) {
+    _cancelDependencySubscriptions(info);
     if (info.packageRoot != null) {
       info.packageMapInfo = null;
       JavaFile packagesDir = new JavaFile(info.packageRoot);
@@ -425,6 +436,19 @@ abstract class ContextManager {
             _packageMapProvider.computePackageMap(folder, info.packageMapInfo);
       });
       endComputePackageMap();
+      for (String dependencyPath in packageMapInfo.dependencies) {
+        Resource resource = resourceProvider.getResource(dependencyPath);
+        if (resource is File) {
+          info.dependencySubscriptions.add(resource.changes
+              .listen((WatchEvent event) {
+            if (info.packageMapInfo != null &&
+                info.packageMapInfo.isChangedDependency(
+                    dependencyPath, resourceProvider)) {
+              _recomputePackageUriResolver(info);
+            }
+          }));
+        }
+      }
       info.packageMapInfo = packageMapInfo;
       if (packageMapInfo.packageMap == null) {
         return null;
@@ -513,7 +537,9 @@ abstract class ContextManager {
    * Clean up and destroy the context associated with the given folder.
    */
   void _destroyContext(Folder folder) {
-    _contexts[folder].changeSubscription.cancel();
+    _ContextInfo info = _contexts[folder];
+    info.changeSubscription.cancel();
+    _cancelDependencySubscriptions(info);
     removeContext(folder);
     _contexts.remove(folder);
   }
@@ -749,6 +775,13 @@ class _ContextInfo {
   StreamSubscription<WatchEvent> changeSubscription;
 
   /**
+   * Stream subscriptions we are using to watch the files
+   * used to determine the package map.
+   */
+  final List<StreamSubscription<WatchEvent>> dependencySubscriptions =
+      <StreamSubscription<WatchEvent>>[];
+
+  /**
    * The analysis context that was created for the [folder].
    */
   AnalysisContext context;