Skip extension host restart when adding the first folder to an empty window

src/vs/workbench/contrib/relauncher/browser/relauncher.contribution.ts

@@ -340,9 +340,13 @@ export class WorkspaceChangeExtHostRelauncher extends Disposable implements IWor
 		// Restart extension host if first root folder changed (impact on deprecated workspace.rootPath API)
 		const newFirstFolderResource = workspace.folders.length > 0 ? workspace.folders[0].uri : undefined;
 		if (!isEqual(this.firstFolderResource, newFirstFolderResource)) {
+			const hadFirstFolder = !!this.firstFolderResource;
 			this.firstFolderResource = newFirstFolderResource;
 
-			this.extensionHostRestarter.schedule(); // buffer calls to extension host restart
+			// Skip 0→1 folders (#319944): same as adding a folder in an existing workspace
+			if (hadFirstFolder) {
+				this.extensionHostRestarter.schedule(); // buffer calls to extension host restart
+			}
 		}
 	}
 }

src/vs/workbench/services/workspaces/electron-browser/workspaceEditingService.ts

@@ -6,7 +6,7 @@
 import { localize } from '../../../../nls.js';
 import { IWorkspaceEditingService } from '../common/workspaceEditing.js';
 import { URI } from '../../../../base/common/uri.js';
-import { hasWorkspaceFileExtension, isUntitledWorkspace, isWorkspaceIdentifier, IWorkspaceContextService, toWorkspaceIdentifier } from '../../../../platform/workspace/common/workspace.js';
+import { hasWorkspaceFileExtension, isUntitledWorkspace, isWorkspaceIdentifier, IWorkspaceContextService, toWorkspaceIdentifier, WorkbenchState } from '../../../../platform/workspace/common/workspace.js';
 import { IJSONEditingService } from '../../configuration/common/jsonEditing.js';
 import { IWorkspacesService } from '../../../../platform/workspaces/common/workspaces.js';
 import { WorkspaceService } from '../../configuration/browser/configurationService.js';
@@ -176,9 +176,14 @@ export class NativeWorkspaceEditingService extends AbstractWorkspaceEditingServi
 	}
 
 	async enterWorkspace(workspaceUri: URI): Promise<void> {
-		const stopped = await this.extensionService.stopExtensionHosts(localize('restartExtensionHost.reason', "Opening a multi-root workspace"));
-		if (!stopped) {
-			return;
+		// Skip extension host restart when coming from an empty window (#319944)
+		const fromEmptyWorkspace = this.contextService.getWorkbenchState() === WorkbenchState.EMPTY;
+
+		if (!fromEmptyWorkspace) {
+			const stopped = await this.extensionService.stopExtensionHosts(localize('restartExtensionHost.reason', "Opening a multi-root workspace"));
+			if (!stopped) {
+				return;
+			}
 		}
 
 		const oldWorkspace = toWorkspaceIdentifier(this.contextService.getWorkspace());
@@ -205,7 +210,7 @@ export class NativeWorkspaceEditingService extends AbstractWorkspaceEditingServi
 
 		// Restart the extension host: entering a workspace means a new location for
 		// storage and potentially a change in the workspace.rootPath property.
-		else {
+		else if (!fromEmptyWorkspace) {
 			this.extensionService.startExtensionHosts();
 		}
 	}

src/vs/workbench/services/workspaces/test/electron-browser/nativeWorkspaceEditingService.test.ts

@@ -0,0 +1,77 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the MIT License. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+import assert from 'assert';
+import { URI } from '../../../../../base/common/uri.js';
+import { mock } from '../../../../../base/test/common/mock.js';
+import { ensureNoDisposablesAreLeakedInTestSuite } from '../../../../../base/test/common/utils.js';
+import { IWorkspaceContextService, toWorkspaceFolder, WorkbenchState } from '../../../../../platform/workspace/common/workspace.js';
+import { Workspace } from '../../../../../platform/workspace/test/common/testWorkspace.js';
+import { IJSONEditingService } from '../../../configuration/common/jsonEditing.js';
+import { IExtensionService } from '../../../extensions/common/extensions.js';
+import { NativeWorkspaceEditingService } from '../../electron-browser/workspaceEditingService.js';
+import { TestContextService } from '../../../../test/common/workbenchTestServices.js';
+import { workbenchInstantiationService } from '../../../../test/electron-browser/workbenchTestServices.js';
+import { TestInstantiationService } from '../../../../../platform/instantiation/test/common/instantiationServiceMock.js';
+
+class TestNativeWorkspaceEditingService extends NativeWorkspaceEditingService {
+	protected override async doEnterWorkspace(workspaceUri: URI) {
+		return { workspace: { id: 'test-workspace', configPath: workspaceUri } };
+	}
+}
+
+suite('NativeWorkspaceEditingService', () => {
+
+	const disposables = ensureNoDisposablesAreLeakedInTestSuite();
+
+	let instantiationService: TestInstantiationService;
+	const workspaceUri = URI.file('/test/Untitled-1.code-workspace');
+
+	setup(() => {
+		disposables.add(instantiationService = workbenchInstantiationService(undefined, disposables));
+		instantiationService.stub(IJSONEditingService, new class extends mock<IJSONEditingService>() { });
+	});
+
+	function createExtensionService(): { stopCalls: number; startCalls: number } {
+		const calls = { stopCalls: 0, startCalls: 0 };
+		instantiationService.stub(IExtensionService, new class extends mock<IExtensionService>() {
+			override stopExtensionHosts() {
+				calls.stopCalls++;
+				return Promise.resolve(true);
+			}
+			override startExtensionHosts() {
+				calls.startCalls++;
+				return Promise.resolve();
+			}
+		});
+		return calls;
+	}
+
+	test('enterWorkspace from empty window does not restart extension host', async () => {
+		const contextService = new TestContextService(new Workspace('empty-workspace'));
+		assert.strictEqual(contextService.getWorkbenchState(), WorkbenchState.EMPTY);
+		instantiationService.stub(IWorkspaceContextService, contextService);
+
+		const extensionService = createExtensionService();
+		const service = disposables.add(instantiationService.createInstance(TestNativeWorkspaceEditingService));
+		await service.enterWorkspace(workspaceUri);
+
+		assert.strictEqual(extensionService.stopCalls, 0);
+		assert.strictEqual(extensionService.startCalls, 0);
+	});
+
+	test('enterWorkspace from folder window restarts extension host', async () => {
+		const contextService = new TestContextService(new Workspace('folder-workspace', [toWorkspaceFolder(URI.file('/test/folder'))]));
+		assert.strictEqual(contextService.getWorkbenchState(), WorkbenchState.FOLDER);
+		instantiationService.stub(IWorkspaceContextService, contextService);
+
+		const extensionService = createExtensionService();
+		const service = disposables.add(instantiationService.createInstance(TestNativeWorkspaceEditingService));
+		await service.enterWorkspace(workspaceUri);
+
+		assert.strictEqual(extensionService.stopCalls, 1);
+		assert.strictEqual(extensionService.startCalls, 1);
+	});
+});