use `getOrCreateMode` and move api to proposed-stage first

src/vs/editor/common/services/languagesRegistry.ts

@@ -211,10 +211,6 @@ export class LanguagesRegistry {
 		return Object.keys(this._nameMap);
 	}
 
-	public isRegisteredModeExact(modeId: string): boolean {
-		return hasOwnProperty.call(this._languages, modeId);
-	}
-
 	public getLanguageName(modeId: string): string {
 		if (!hasOwnProperty.call(this._languages, modeId)) {
 			return null;

src/vs/editor/common/services/modeService.ts

@@ -46,6 +46,5 @@ export interface IModeService {
 	getMode(commaSeparatedMimetypesOrCommaSeparatedIds: string): IMode;
 	getOrCreateMode(commaSeparatedMimetypesOrCommaSeparatedIds: string): TPromise<IMode>;
 	getOrCreateModeByLanguageName(languageName: string): TPromise<IMode>;
-	getOrCreateModeByLanguageId(modeId: string): TPromise<IMode>;
 	getOrCreateModeByFilenameOrFirstLine(filename: string, firstLine?: string): TPromise<IMode>;
 }

src/vs/editor/common/services/modeServiceImpl.ts

@@ -132,15 +132,6 @@ export class ModeServiceImpl implements IModeService {
 		});
 	}
 
-	public getOrCreateModeByLanguageId(modeId: string): TPromise<IMode> {
-		return this._onReady().then(() => {
-			if (!this._registry.isRegisteredModeExact(modeId)) {
-				modeId = 'plaintext';
-			}
-			return this._getOrCreateMode(modeId);
-		});
-	}
-
 	private _getModeIdByLanguageName(languageName: string): string {
 		const modeIds = this._registry.getModeIdsFromLanguageName(languageName);
 

src/vs/vscode.d.ts

@@ -7375,8 +7375,6 @@ declare module 'vscode' {
 	 */
 	export namespace languages {
 
-		export function changeLanguage(document: TextDocument, languageId: string): Thenable<void>;
-
 		/**
 		 * Return the identifiers of all known languages.
 		 * @return Promise resolving to an array of identifier strings.

src/vs/vscode.proposed.d.ts

@@ -5,7 +5,6 @@
 
 // This is the place for API experiments and proposal.
 
-import { QuickPickItem } from 'vscode';
 
 declare module 'vscode' {
 
@@ -13,6 +12,14 @@ declare module 'vscode' {
 		export function sampleFunction(): Thenable<any>;
 	}
 
+	export namespace languages {
+
+		/**
+		 *
+		 */
+		export function changeLanguage(document: TextDocument, languageId: string): Thenable<void>;
+	}
+
 	//#region Rob: search provider
 
 	/**

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

@@ -39,8 +39,12 @@ export class MainThreadLanguages implements MainThreadLanguagesShape {
 		if (!model) {
 			return TPromise.wrapError(new Error('Invalid uri'));
 		}
-		let mode = this._modeService.getOrCreateModeByLanguageId(languageId);
-		this._modelService.setMode(model, mode);
-		return TPromise.as(null);
+		return this._modeService.getOrCreateMode(languageId).then(mode => {
+			if (mode.getId() !== languageId) {
+				return TPromise.wrapError<void>(new Error(`Unknown language id: ${languageId}`));
+			}
+			this._modelService.setMode(model, mode);
+			return undefined;
+		});
 	}
 }

src/vs/workbench/api/node/extHost.api.impl.ts

@@ -259,6 +259,7 @@ export function createApiFactory(
 				return extHostLanguages.getLanguages();
 			},
 			changeLanguage(document: vscode.TextDocument, languageId: string): TPromise<void> {
+				checkProposedApiEnabled(extension);
 				return extHostLanguages.changeLanguage(document.uri, languageId);
 			},
 			match(selector: vscode.DocumentSelector, document: vscode.TextDocument): number {