[analysis_server] Skip analysis work when overlays are created if con…

…tent matches previous content-

May prevent #48051 from occurring since we will no longer call driver.changeFile() for SDK libraries being opened, although it does not resolve the underlying issue.

Change-Id: I5ca53a04842348a584ccc824aaf90ba7f230c002
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/251980
Commit-Queue: Brian Wilkerson <brianwilkerson@google.com>
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>

pkg/analysis_server/lib/src/lsp/handlers/handler_text_document_changes.dart

@@ -103,10 +103,6 @@ class TextDocumentOpenHandler
       );
       server.onOverlayCreated(path, doc.text);
 
-      // If the file did not exist, and is "overlay only", it still should be
-      // analyzed. Add it to driver to which it should have been added.
-      server.contextManager.getDriverFor(path)?.addFile(path);
-
       await server.addPriorityFile(path);
 
       return success(null);

pkg/analysis_server/lib/src/lsp/lsp_analysis_server.dart

@@ -497,10 +497,33 @@ class LspAnalysisServer extends AbstractAnalysisServer {
   }
 
   void onOverlayCreated(String path, String content) {
+    final currentFile = resourceProvider.getFile(path);
+    String? currentContent;
+
+    try {
+      currentContent = currentFile.readAsStringSync();
+    } on FileSystemException {
+      // It's possible we're creating an overlay for a file that doesn't yet
+      // exist on disk so must handle missing file exceptions. Checking for
+      // exists first would introduce a race.
+    }
+
     resourceProvider.setOverlay(path,
         content: content, modificationStamp: overlayModificationStamp++);
 
-    _afterOverlayChanged(path, plugin.AddContentOverlay(content));
+    // If the overlay is exactly the same as the previous content we can skip
+    // notifying drivers which avoids re-analyzing the same content.
+    if (content != currentContent) {
+      _afterOverlayChanged(path, plugin.AddContentOverlay(content));
+
+      // If the file did not exist, and is "overlay only", it still should be
+      // analyzed. Add it to driver to which it should have been added.
+      contextManager.getDriverFor(path)?.addFile(path);
+    } else {
+      // If we skip the work above, we still need to ensure plugins are notified
+      // of the new overlay (which usually happens in `_afterOverlayChanged`).
+      _notifyPluginsOverlayChanged(path, plugin.AddContentOverlay(content));
+    }
   }
 
   void onOverlayDestroyed(String path) {
@@ -772,9 +795,7 @@ class LspAnalysisServer extends AbstractAnalysisServer {
     for (var driver in driverMap.values) {
       driver.changeFile(path);
     }
-    pluginManager.setAnalysisUpdateContentParams(
-      plugin.AnalysisUpdateContentParams({path: changeForPlugins}),
-    );
+    _notifyPluginsOverlayChanged(path, changeForPlugins);
 
     notifyDeclarationsTracker(path);
     notifyFlutterWidgetDescriptions(path);
@@ -834,6 +855,13 @@ class LspAnalysisServer extends AbstractAnalysisServer {
     }
   }
 
+  void _notifyPluginsOverlayChanged(
+      String path, plugin.HasToJson changeForPlugins) {
+    pluginManager.setAnalysisUpdateContentParams(
+      plugin.AnalysisUpdateContentParams({path: changeForPlugins}),
+    );
+  }
+
   void _onPluginsChanged() {
     capabilitiesComputer.performDynamicRegistration();
   }

pkg/analysis_server/test/lsp/document_changes_test.dart

@@ -114,6 +114,49 @@ class Bar {
     expect(driverForInside.addedFiles, isNot(contains(fileOutsideRootPath)));
   }
 
+  Future<void> test_documentOpen_contentChanged_analysis() async {
+    const content = '// original content';
+    const newContent = '// new content';
+    newFile(mainFilePath, content);
+
+    // Wait for initial analysis to provide diagnostics for the file.
+    await Future.wait([
+      waitForDiagnostics(mainFileUri),
+      initialize(),
+    ]);
+
+    // Capture any further diagnostics sent after we open the file.
+    List<Diagnostic>? diagnostics;
+    unawaited(waitForDiagnostics(mainFileUri).then((d) => diagnostics = d));
+    await openFile(mainFileUri, newContent);
+    await pumpEventQueue(times: 5000);
+
+    // Expect diagnostics, because changing the content will have triggered
+    // analysis.
+    expect(diagnostics, isNotNull);
+  }
+
+  Future<void> test_documentOpen_contentUnchanged_noAnalysis() async {
+    const content = '// original content';
+    newFile(mainFilePath, content);
+
+    // Wait for initial analysis to provide diagnostics for the file.
+    await Future.wait([
+      waitForDiagnostics(mainFileUri),
+      initialize(),
+    ]);
+
+    // Capture any further diagnostics sent after we open the file.
+    List<Diagnostic>? diagnostics;
+    unawaited(waitForDiagnostics(mainFileUri).then((d) => diagnostics = d));
+    await openFile(mainFileUri, content);
+    await pumpEventQueue(times: 5000);
+
+    // Expect no diagnostics because the file didn't actually change content
+    // when the overlay was created, so it should not have triggered analysis.
+    expect(diagnostics, isNull);
+  }
+
   Future<void> test_documentOpen_createsOverlay() async {
     await _initializeAndOpen();