Made browser to expose pylance api. (#20847)

This will let pylance to create LS Client on browser

src/client/browser/api.ts

@@ -0,0 +1,35 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+
+'use strict';
+
+import { BaseLanguageClient } from 'vscode-languageclient';
+import { LanguageClient } from 'vscode-languageclient/browser';
+import { PYTHON_LANGUAGE } from '../common/constants';
+
+export interface IBrowserExtensionApi {
+    /**
+     * @deprecated Temporarily exposed for Pylance until we expose this API generally. Will be removed in an
+     * iteration or two.
+     */
+    pylance: {
+        // eslint-disable-next-line @typescript-eslint/no-explicit-any
+        createClient(...args: any[]): BaseLanguageClient;
+        start(client: BaseLanguageClient): Promise<void>;
+        stop(client: BaseLanguageClient): Promise<void>;
+    };
+}
+
+export function buildApi(): IBrowserExtensionApi {
+    const api: IBrowserExtensionApi = {
+        pylance: {
+            // eslint-disable-next-line @typescript-eslint/no-explicit-any
+            createClient: (...args: any[]): BaseLanguageClient =>
+                new LanguageClient(PYTHON_LANGUAGE, 'Python Language Server', args[0], args[1]),
+            start: (client: BaseLanguageClient): Promise<void> => client.start(),
+            stop: (client: BaseLanguageClient): Promise<void> => client.stop(),
+        },
+    };
+
+    return api;
+}

src/client/browser/extension.ts

@@ -11,6 +11,7 @@ import { AppinsightsKey, PYLANCE_EXTENSION_ID } from '../common/constants';
 import { EventName } from '../telemetry/constants';
 import { createStatusItem } from './intellisenseStatus';
 import { PylanceApi } from '../activation/node/pylanceApi';
+import { buildApi, IBrowserExtensionApi } from './api';
 
 interface BrowserConfig {
     distUrl: string; // URL to Pylance's dist folder.
@@ -19,11 +20,11 @@ interface BrowserConfig {
 let languageClient: LanguageClient | undefined;
 let pylanceApi: PylanceApi | undefined;
 
-export async function activate(context: vscode.ExtensionContext): Promise<void> {
+export async function activate(context: vscode.ExtensionContext): Promise<IBrowserExtensionApi> {
     const pylanceExtension = vscode.extensions.getExtension<PylanceApi>(PYLANCE_EXTENSION_ID);
     if (pylanceExtension) {
         await runPylance(context, pylanceExtension);
-        return;
+        return buildApi();
     }
 
     const changeDisposable = vscode.extensions.onDidChange(async () => {
@@ -33,6 +34,8 @@ export async function activate(context: vscode.ExtensionContext): Promise<void>
             await runPylance(context, newPylanceExtension);
         }
     });
+
+    return buildApi();
 }
 
 export async function deactivate(): Promise<void> {