VSCode merge (#4610)

* Merge from vscode e388c734f30757875976c7e326d6cfeee77710de

* fix yarn lcoks

* remove small issue

src/vs/workbench/api/browser/mainThreadLanguages.ts

@@ -0,0 +1,43 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the Source EULA. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+import { URI, UriComponents } from 'vs/base/common/uri';
+import { IModeService } from 'vs/editor/common/services/modeService';
+import { IModelService } from 'vs/editor/common/services/modelService';
+import { MainThreadLanguagesShape, MainContext, IExtHostContext } from '../common/extHost.protocol';
+import { extHostNamedCustomer } from 'vs/workbench/api/common/extHostCustomers';
+
+@extHostNamedCustomer(MainContext.MainThreadLanguages)
+export class MainThreadLanguages implements MainThreadLanguagesShape {
+
+	constructor(
+		_extHostContext: IExtHostContext,
+		@IModeService private readonly _modeService: IModeService,
+		@IModelService private readonly _modelService: IModelService
+	) {
+	}
+
+	dispose(): void {
+		// nothing
+	}
+
+	$getLanguages(): Promise<string[]> {
+		return Promise.resolve(this._modeService.getRegisteredModes());
+	}
+
+	$changeLanguage(resource: UriComponents, languageId: string): Promise<void> {
+		const uri = URI.revive(resource);
+		const model = this._modelService.getModel(uri);
+		if (!model) {
+			return Promise.reject(new Error('Invalid uri'));
+		}
+		const languageIdentifier = this._modeService.getLanguageIdentifier(languageId);
+		if (!languageIdentifier || languageIdentifier.language !== languageId) {
+			return Promise.reject(new Error(`Unknown language id: ${languageId}`));
+		}
+		this._modelService.setMode(model, this._modeService.create(languageId));
+		return Promise.resolve(undefined);
+	}
+}