Refresh config file diagnostics when a config file is saved

internal/project/project_test.go

@@ -411,6 +411,40 @@ func TestPushDiagnostics(t *testing.T) {
 		assert.Equal(t, len(lastTsconfigCall.Params.Diagnostics), 0, "expected no diagnostics after removing baseUrl option")
 	})
 
+	t.Run("updates diagnostics when an open config file is saved", func(t *testing.T) {
+		t.Parallel()
+		files := map[string]any{
+			"/src/tsconfig.json": `{"compilerOptions": {"target": "es2020"}}`,
+			"/src/index.ts":      "export const x = 1;",
+		}
+		session, utils := projecttestutil.Setup(files)
+		session.DidOpenFile(context.Background(), "file:///src/index.ts", 1, files["/src/index.ts"].(string), lsproto.LanguageKindTypeScript)
+		_, err := session.GetLanguageService(context.Background(), lsproto.DocumentUri("file:///src/index.ts"))
+		assert.NilError(t, err)
+		session.WaitForBackgroundTasks()
+
+		// Edit the config file in the editor and save it. No other request follows, so the
+		// save is what has to get the new diagnostics published.
+		newContent := `{"compilerOptions": {"target": "es5"}}`
+		session.DidOpenFile(context.Background(), "file:///src/tsconfig.json", 1, files["/src/tsconfig.json"].(string), lsproto.LanguageKindJSON)
+		session.DidChangeFile(context.Background(), "file:///src/tsconfig.json", 2, []lsproto.TextDocumentContentChangePartialOrWholeDocument{
+			{WholeDocument: &lsproto.TextDocumentContentChangeWholeDocument{Text: newContent}},
+		})
+		assert.NilError(t, utils.FS().WriteFile("/src/tsconfig.json", newContent))
+		session.DidSaveFile(context.Background(), "file:///src/tsconfig.json")
+		session.WaitForBackgroundTasks()
+
+		calls := utils.Client().PublishDiagnosticsCalls()
+		tsconfigCalls := filterDiagnosticsByURI(calls, "file:///src/tsconfig.json", 0)
+		assert.Assert(t, len(tsconfigCalls) > 0, "expected PublishDiagnostics call for tsconfig.json")
+		lastTsconfigCall := tsconfigCalls[len(tsconfigCalls)-1]
+
+		expectedMessage := "Option 'target=ES5' has been removed."
+		assert.Assert(t, slices.ContainsFunc(lastTsconfigCall.Params.Diagnostics, func(diag *lsproto.Diagnostic) bool {
+			return strings.Contains(diag.Message.AsString(), expectedMessage)
+		}), "expected removed target diagnostic on tsconfig.json, got: %v", lastTsconfigCall.Params.Diagnostics)
+	})
+
 	t.Run("does not publish for inferred projects", func(t *testing.T) {
 		t.Parallel()
 		files := map[string]any{

internal/project/session.go

@@ -44,6 +44,7 @@ const (
 	UpdateReasonRequestedLoadProjectTree
 	UpdateReasonRequestedLanguageServiceWithAutoImports
 	UpdateReasonIdleCleanDiskCache
+	UpdateReasonDidSaveConfigFile
 )
 
 // watchRequestTimeout is the maximum time to wait for the client to respond to
@@ -360,11 +361,32 @@ func (s *Session) DidChangeFile(ctx context.Context, uri lsproto.DocumentUri, ve
 func (s *Session) DidSaveFile(ctx context.Context, uri lsproto.DocumentUri) {
 	s.scheduleIdleCacheClean()
 	s.pendingFileChangesMu.Lock()
-	defer s.pendingFileChangesMu.Unlock()
 	s.pendingFileChanges = append(s.pendingFileChanges, FileChange{
 		Kind: FileChangeKindSave,
 		URI:  uri,
 	})
+	s.pendingFileChangesMu.Unlock()
+
+	if s.isConfigFile(uri) {
+		// Diagnostics for config files are only pushed as part of a snapshot update.
+		// Editing a config file usually isn't followed by any request that would flush
+		// the pending changes, so schedule an update to get its diagnostics republished.
+		s.ScheduleSnapshotUpdate(UpdateReasonDidSaveConfigFile)
+	}
+}
+
+// isConfigFile returns true if the given file is a config file known to the current
+// snapshot, or is named like one.
+func (s *Session) isConfigFile(uri lsproto.DocumentUri) bool {
+	fileName := uri.FileName()
+	baseName := tspath.GetBaseFileName(fileName)
+	snapshot := s.Snapshot()
+	if baseName == "tsconfig.json" || baseName == "jsconfig.json" ||
+		(snapshot.ConfigFileRegistry.customConfigFileName != "" && baseName == snapshot.ConfigFileRegistry.customConfigFileName) {
+		return true
+	}
+	// Configs pulled in by `extends` or project references can be named anything.
+	return snapshot.ConfigFileRegistry.GetConfig(snapshot.toPath(fileName)) != nil
 }
 
 func (s *Session) DidChangeWatchedFiles(ctx context.Context, changes []*lsproto.FileEvent) {

internal/project/snapshot.go

@@ -268,6 +268,8 @@ func (s *Snapshot) Clone(ctx context.Context, change SnapshotChange, overlays ma
 			logger.Logf("Reason: DidOpenFile - %s", change.fileChanges.Opened)
 		case UpdateReasonDidCloseFile:
 			logger.Logf("Reason: DidCloseFile - %v", change.fileChanges.Closed)
+		case UpdateReasonDidSaveConfigFile:
+			logger.Logf("Reason: DidSaveConfigFile - %v", change.fileChanges.Changed)
 		case UpdateReasonDidChangeCompilerOptionsForInferredProjects:
 			logger.Logf("Reason: DidChangeCompilerOptionsForInferredProjects")
 		case UpdateReasonRequestedLanguageServicePendingChanges: