Support refresh of individual analysis roots (issue 22254)

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 c76ac5e9b43cd9ce02feba13ef84b47dc072c209..62a6ce76a5a1a4451d5457224f1f459461d3d2e8 100644
--- a/pkg/analysis_server/lib/src/context_manager.dart
+++ b/pkg/analysis_server/lib/src/context_manager.dart
@@ -164,12 +164,24 @@ abstract class ContextManager {
 
   /**
    * Rebuild the set of contexts from scratch based on the data last sent to
-   * setRoots().
+   * setRoots(). Only contexts contained in the given list of analysis [roots]
+   * will be rebuilt, unless the list is `null`, in which case every context
+   * will be rebuilt.
    */
-  void refresh() {
+  void refresh(List<Resource> roots) {
     // Destroy old contexts
     List<Folder> contextFolders = _contexts.keys.toList();
-    contextFolders.forEach(_destroyContext);
+    if (roots == null) {
+      contextFolders.forEach(_destroyContext);
+    } else {
+      roots.forEach((Resource resource) {
+        contextFolders.forEach((Folder contextFolder) {
+          if (resource is Folder && resource.isOrContains(contextFolder.path)) {
+            _destroyContext(contextFolder);
+          }
+        });
+      });
+    }
 
     // Rebuild contexts based on the data last sent to setRoots().
     setRoots(includedPaths, excludedPaths, packageRoots);