Disable language services if Pyrefly extension installed + active (#24987)

For #24850

Summary:
Background:
A new typechecker called Pyrefly will be featured at Pycon with a
[talk](https://us.pycon.org/2025/schedule/presentation/118/),
[website/sandbox](https://pyrefly.org/) (still WIP), and
[extension](https://marketplace.visualstudio.com/items?itemName=meta.pyrefly)
(still WIP). This extension will provide ultrafast typechecking and
language services. When the Pyrefly extension is installed,
`ms-python.python` should not start Jedi or Pylance unless
[`python.pyrefly.disableLanguageServices`](facebook/pyrefly@4d7e23c)
is set to `true`.


Because of the separation of vscode's `getExtensions` API and config
reading logic, I chose to augment `DefaultLSType` with fallback
information in case Pyrefly is disabled. This lets `configSettings` pick
the correct jedi/pylance without knowing if Pyrefly will be enabled or
disabled.

Test Plan:
still can't get pyright to work in the local extension build but I do
see my breakpoints hit and the correct languageServer set


https://github.com/user-attachments/assets/395bacbb-7ad0-4357-b084-cd5e88062801

Author: kinto0

src/client/common/configSettings.ts

@@ -21,11 +21,12 @@ import { sendSettingTelemetry } from '../telemetry/envFileTelemetry';
 import { ITestingSettings } from '../testing/configuration/types';
 import { IWorkspaceService } from './application/types';
 import { WorkspaceService } from './application/workspace';
-import { DEFAULT_INTERPRETER_SETTING, isTestExecution } from './constants';
+import { DEFAULT_INTERPRETER_SETTING, isTestExecution, PYREFLY_EXTENSION_ID } from './constants';
 import {
     IAutoCompleteSettings,
     IDefaultLanguageServer,
     IExperiments,
+    IExtensions,
     IInterpreterPathService,
     IInterpreterSettings,
     IPythonSettings,
@@ -140,6 +141,7 @@ export class PythonSettings implements IPythonSettings {
         workspace: IWorkspaceService,
         private readonly interpreterPathService: IInterpreterPathService,
         private readonly defaultLS: IDefaultLanguageServer | undefined,
+        private readonly extensions: IExtensions,
     ) {
         this.workspace = workspace || new WorkspaceService();
         this.workspaceRoot = workspaceFolder;
@@ -152,6 +154,7 @@ export class PythonSettings implements IPythonSettings {
         workspace: IWorkspaceService,
         interpreterPathService: IInterpreterPathService,
         defaultLS: IDefaultLanguageServer | undefined,
+        extensions: IExtensions,
     ): PythonSettings {
         workspace = workspace || new WorkspaceService();
         const workspaceFolderUri = PythonSettings.getSettingsUriAndTarget(resource, workspace).uri;
@@ -164,6 +167,7 @@ export class PythonSettings implements IPythonSettings {
                 workspace,
                 interpreterPathService,
                 defaultLS,
+                extensions,
             );
             PythonSettings.pythonSettings.set(workspaceFolderKey, settings);
             settings.onDidChange((event) => PythonSettings.debounceConfigChangeNotification(event));
@@ -275,7 +279,14 @@ export class PythonSettings implements IPythonSettings {
             userLS === 'Microsoft' ||
             !Object.values(LanguageServerType).includes(userLS as LanguageServerType)
         ) {
-            this.languageServer = this.defaultLS?.defaultLSType ?? LanguageServerType.None;
+            if (
+                this.extensions.getExtension(PYREFLY_EXTENSION_ID) &&
+                pythonSettings.get<boolean>('pyrefly.disableLanguageServices') !== true
+            ) {
+                this.languageServer = LanguageServerType.None;
+            } else {
+                this.languageServer = this.defaultLS?.defaultLSType ?? LanguageServerType.None;
+            }
             this.languageServerIsDefault = true;
         } else if (userLS === 'JediLSP') {
             // Switch JediLSP option to Jedi.

src/client/common/configuration/service.ts

@@ -8,7 +8,13 @@ import { IServiceContainer } from '../../ioc/types';
 import { IWorkspaceService } from '../application/types';
 import { PythonSettings } from '../configSettings';
 import { isUnitTestExecution } from '../constants';
-import { IConfigurationService, IDefaultLanguageServer, IInterpreterPathService, IPythonSettings } from '../types';
+import {
+    IConfigurationService,
+    IDefaultLanguageServer,
+    IExtensions,
+    IInterpreterPathService,
+    IPythonSettings,
+} from '../types';
 
 @injectable()
 export class ConfigurationService implements IConfigurationService {
@@ -29,12 +35,14 @@ export class ConfigurationService implements IConfigurationService {
         );
         const interpreterPathService = this.serviceContainer.get<IInterpreterPathService>(IInterpreterPathService);
         const defaultLS = this.serviceContainer.tryGet<IDefaultLanguageServer>(IDefaultLanguageServer);
+        const extensions = this.serviceContainer.get<IExtensions>(IExtensions);
         return PythonSettings.getInstance(
             resource,
             InterpreterAutoSelectionService,
             this.workspaceService,
             interpreterPathService,
             defaultLS,
+            extensions,
         );
     }
 

src/client/common/constants.ts

@@ -22,6 +22,7 @@ export const PYTHON_NOTEBOOKS = [
 
 export const PVSC_EXTENSION_ID = 'ms-python.python';
 export const PYLANCE_EXTENSION_ID = 'ms-python.vscode-pylance';
+export const PYREFLY_EXTENSION_ID = 'meta.pyrefly';
 export const JUPYTER_EXTENSION_ID = 'ms-toolsai.jupyter';
 export const TENSORBOARD_EXTENSION_ID = 'ms-toolsai.tensorboard';
 export const AppinsightsKey = '0c6ae279ed8443289764825290e4f9e2-1a736e7c-1324-4338-be46-fc2a58ae4d14-7255';

src/test/common/configSettings/configSettings.pythonPath.unit.test.ts

@@ -17,6 +17,7 @@ import { PythonEnvironment } from '../../../client/pythonEnvironments/info';
 import * as EnvFileTelemetry from '../../../client/telemetry/envFileTelemetry';
 import { MockAutoSelectionService } from '../../mocks/autoSelector';
 import { untildify } from '../../../client/common/helpers';
+import { MockExtensions } from '../../mocks/extensions';
 
 suite('Python Settings - pythonPath', () => {
     class CustomPythonSettings extends PythonSettings {
@@ -64,6 +65,7 @@ suite('Python Settings - pythonPath', () => {
             workspaceService.object,
             interpreterPathService.object,
             undefined,
+            new MockExtensions(),
         );
         configSettings.update(pythonSettings.object);
 
@@ -78,6 +80,7 @@ suite('Python Settings - pythonPath', () => {
             workspaceService.object,
             interpreterPathService.object,
             undefined,
+            new MockExtensions(),
         );
         configSettings.update(pythonSettings.object);
 
@@ -93,6 +96,7 @@ suite('Python Settings - pythonPath', () => {
             workspaceService.object,
             interpreterPathService.object,
             undefined,
+            new MockExtensions(),
         );
 
         configSettings.update(pythonSettings.object);
@@ -110,6 +114,7 @@ suite('Python Settings - pythonPath', () => {
             workspaceService.object,
             interpreterPathService.object,
             undefined,
+            new MockExtensions(),
         );
         configSettings.update(pythonSettings.object);
 
@@ -126,6 +131,7 @@ suite('Python Settings - pythonPath', () => {
             workspaceService.object,
             interpreterPathService.object,
             undefined,
+            new MockExtensions(),
         );
         configSettings.update(pythonSettings.object);
 
@@ -145,6 +151,7 @@ suite('Python Settings - pythonPath', () => {
             workspaceService.object,
             interpreterPathService.object,
             undefined,
+            new MockExtensions(),
         );
         configSettings.update(pythonSettings.object);
 
@@ -166,6 +173,7 @@ suite('Python Settings - pythonPath', () => {
             workspaceService.object,
             interpreterPathService.object,
             undefined,
+            new MockExtensions(),
         );
         configSettings.update(pythonSettings.object);
 
@@ -184,6 +192,7 @@ suite('Python Settings - pythonPath', () => {
             workspaceService.object,
             interpreterPathService.object,
             undefined,
+            new MockExtensions(),
         );
         interpreterPathService.setup((i) => i.get(typemoq.It.isAny())).returns(() => 'custom');
         pythonSettings.setup((p) => p.get(typemoq.It.isValue('defaultInterpreterPath'))).returns(() => 'python');
@@ -204,6 +213,7 @@ suite('Python Settings - pythonPath', () => {
             workspaceService.object,
             interpreterPathService.object,
             undefined,
+            new MockExtensions(),
         );
         interpreterPathService.setup((i) => i.get(resource)).returns(() => 'python');
         configSettings.update(pythonSettings.object);

src/test/common/configSettings/configSettings.unit.test.ts

@@ -27,6 +27,7 @@ import { ITestingSettings } from '../../../client/testing/configuration/types';
 import { MockAutoSelectionService } from '../../mocks/autoSelector';
 import { MockMemento } from '../../mocks/mementos';
 import { untildify } from '../../../client/common/helpers';
+import { MockExtensions } from '../../mocks/extensions';
 
 suite('Python Settings', async () => {
     class CustomPythonSettings extends PythonSettings {
@@ -40,13 +41,15 @@ suite('Python Settings', async () => {
     let config: TypeMoq.IMock<WorkspaceConfiguration>;
     let expected: CustomPythonSettings;
     let settings: CustomPythonSettings;
+    let extensions: MockExtensions;
     setup(() => {
         sinon.stub(EnvFileTelemetry, 'sendSettingTelemetry').returns();
         config = TypeMoq.Mock.ofType<WorkspaceConfiguration>(undefined, TypeMoq.MockBehavior.Loose);
 
         const workspaceService = new WorkspaceService();
         const workspaceMemento = new MockMemento();
         const globalMemento = new MockMemento();
+        extensions = new MockExtensions();
         const persistentStateFactory = new PersistentStateFactory(globalMemento, workspaceMemento);
         expected = new CustomPythonSettings(
             undefined,
@@ -55,7 +58,8 @@ suite('Python Settings', async () => {
             new InterpreterPathService(persistentStateFactory, workspaceService, [], {
                 remoteName: undefined,
             } as IApplicationEnvironment),
-            undefined,
+            { defaultLSType: LanguageServerType.Jedi },
+            extensions,
         );
         settings = new CustomPythonSettings(
             undefined,
@@ -64,7 +68,8 @@ suite('Python Settings', async () => {
             new InterpreterPathService(persistentStateFactory, workspaceService, [], {
                 remoteName: undefined,
             } as IApplicationEnvironment),
-            undefined,
+            { defaultLSType: LanguageServerType.Jedi },
+            extensions,
         );
         expected.defaultInterpreterPath = 'python';
     });
@@ -226,7 +231,7 @@ suite('Python Settings', async () => {
         const values = [
             { ls: LanguageServerType.Jedi, expected: LanguageServerType.Jedi, default: false },
             { ls: LanguageServerType.JediLSP, expected: LanguageServerType.Jedi, default: false },
-            { ls: LanguageServerType.Microsoft, expected: LanguageServerType.None, default: true },
+            { ls: LanguageServerType.Microsoft, expected: LanguageServerType.Jedi, default: true },
             { ls: LanguageServerType.Node, expected: LanguageServerType.Node, default: false },
             { ls: LanguageServerType.None, expected: LanguageServerType.None, default: false },
         ];
@@ -235,7 +240,48 @@ suite('Python Settings', async () => {
             testLanguageServer(v.ls, v.expected, v.default);
         });
 
-        testLanguageServer('invalid' as LanguageServerType, LanguageServerType.None, true);
+        testLanguageServer('invalid' as LanguageServerType, LanguageServerType.Jedi, true);
+    });
+
+    function testPyreflySettings(pyreflyInstalled: boolean, pyreflyDisabled: boolean, languageServerDisabled: boolean) {
+        test(`pyrefly ${pyreflyInstalled ? 'installed' : 'not installed'} and ${
+            pyreflyDisabled ? 'disabled' : 'enabled'
+        }`, () => {
+            if (pyreflyInstalled) {
+                extensions.extensionIdsToFind = ['meta.pyrefly'];
+            } else {
+                extensions.extensionIdsToFind = [];
+            }
+            config.setup((c) => c.get<boolean>('pyrefly.disableLanguageServices')).returns(() => pyreflyDisabled);
+
+            config
+                .setup((c) => c.get<string>('languageServer'))
+                .returns(() => undefined)
+                .verifiable(TypeMoq.Times.once());
+
+            settings.update(config.object);
+
+            if (languageServerDisabled) {
+                expect(settings.languageServer).to.equal(LanguageServerType.None);
+            } else {
+                expect(settings.languageServer).not.to.equal(LanguageServerType.None);
+            }
+            expect(settings.languageServerIsDefault).to.equal(true);
+            config.verifyAll();
+        });
+    }
+
+    suite('pyrefly languageServer settings', async () => {
+        const values = [
+            { pyreflyInstalled: true, pyreflyDisabled: false, languageServerDisabled: true },
+            { pyreflyInstalled: true, pyreflyDisabled: true, languageServerDisabled: false },
+            { pyreflyInstalled: false, pyreflyDisabled: true, languageServerDisabled: false },
+            { pyreflyInstalled: false, pyreflyDisabled: false, languageServerDisabled: false },
+        ];
+
+        values.forEach((v) => {
+            testPyreflySettings(v.pyreflyInstalled, v.pyreflyDisabled, v.languageServerDisabled);
+        });
     });
 
     function testExperiments(enabled: boolean) {

src/test/extensionSettings.ts

@@ -13,6 +13,7 @@ import { PersistentStateFactory } from '../client/common/persistentState';
 import { IPythonSettings, Resource } from '../client/common/types';
 import { PythonEnvironment } from '../client/pythonEnvironments/info';
 import { MockMemento } from './mocks/mementos';
+import { MockExtensions } from './mocks/extensions';
 
 export function getExtensionSettings(resource: Uri | undefined): IPythonSettings {
     const vscode = require('vscode') as typeof import('vscode');
@@ -41,6 +42,7 @@ export function getExtensionSettings(resource: Uri | undefined): IPythonSettings
     const workspaceMemento = new MockMemento();
     const globalMemento = new MockMemento();
     const persistentStateFactory = new PersistentStateFactory(globalMemento, workspaceMemento);
+    const extensions = new MockExtensions();
     return pythonSettings.PythonSettings.getInstance(
         resource,
         new AutoSelectionService(),
@@ -49,5 +51,6 @@ export function getExtensionSettings(resource: Uri | undefined): IPythonSettings
             remoteName: undefined,
         } as IApplicationEnvironment),
         undefined,
+        extensions,
     );
 }

src/test/mocks/extension.ts

@@ -0,0 +1,16 @@
+import { injectable } from 'inversify';
+import { Extension, ExtensionKind, Uri } from 'vscode';
+
+@injectable()
+export class MockExtension<T> implements Extension<T> {
+    id!: string;
+    extensionUri!: Uri;
+    extensionPath!: string;
+    isActive!: boolean;
+    packageJSON: any;
+    extensionKind!: ExtensionKind;
+    exports!: T;
+    activate(): Thenable<T> {
+        throw new Error('Method not implemented.');
+    }
+}

src/test/mocks/extensions.ts

@@ -0,0 +1,23 @@
+import { injectable } from 'inversify';
+import { IExtensions } from '../../client/common/types';
+import { Extension, Event } from 'vscode';
+import { MockExtension } from './extension';
+
+@injectable()
+export class MockExtensions implements IExtensions {
+    extensionIdsToFind: unknown[] = [];
+    all: readonly Extension<unknown>[] = [];
+    onDidChange: Event<void> = () => {
+        throw new Error('Method not implemented');
+    };
+    getExtension(extensionId: string): Extension<unknown> | undefined;
+    getExtension<T>(extensionId: string): Extension<T> | undefined;
+    getExtension(extensionId: unknown): import('vscode').Extension<unknown> | undefined {
+        if (this.extensionIdsToFind.includes(extensionId)) {
+            return new MockExtension();
+        }
+    }
+    determineExtensionFromCallStack(): Promise<{ extensionId: string; displayName: string }> {
+        throw new Error('Method not implemented.');
+    }
+}