Strict null work

openEditor can return null

src/vs/workbench/contrib/localizations/browser/localizationsActions.ts

@@ -36,13 +36,13 @@ export class ConfigureLocaleAction extends Action {
 		super(id, label);
 	}
 
-	public run(event?: any): Promise<IEditor | undefined> {
+	public run(event?: any): Promise<IEditor | null> {
 		const file = URI.file(join(this.environmentService.appSettingsHome, 'locale.json'));
 		return this.fileService.resolveFile(file).then(undefined, (error) => {
 			return this.fileService.createFile(file, ConfigureLocaleAction.DEFAULT_CONTENT);
-		}).then((stat): Promise<IEditor | undefined> | undefined => {
+		}).then((stat): Promise<IEditor | null> | null => {
 			if (!stat) {
-				return undefined;
+				return null;
 			}
 			return this.editorService.openEditor({
 				resource: stat.resource

src/vs/workbench/services/editor/browser/editorService.ts

@@ -214,11 +214,11 @@ export class EditorService extends Disposable implements EditorServiceImpl {
 
 	//#region openEditor()
 
-	openEditor(editor: IEditorInput, options?: IEditorOptions | ITextEditorOptions, group?: IEditorGroup | GroupIdentifier | SIDE_GROUP_TYPE | ACTIVE_GROUP_TYPE): Promise<IEditor>;
-	openEditor(editor: IResourceInput | IUntitledResourceInput, group?: IEditorGroup | GroupIdentifier | SIDE_GROUP_TYPE | ACTIVE_GROUP_TYPE): Promise<ITextEditor>;
-	openEditor(editor: IResourceDiffInput, group?: IEditorGroup | GroupIdentifier | SIDE_GROUP_TYPE | ACTIVE_GROUP_TYPE): Promise<ITextDiffEditor>;
-	openEditor(editor: IResourceSideBySideInput, group?: IEditorGroup | GroupIdentifier | SIDE_GROUP_TYPE | ACTIVE_GROUP_TYPE): Promise<ITextSideBySideEditor>;
-	openEditor(editor: IEditorInput | IResourceEditor, optionsOrGroup?: IEditorOptions | ITextEditorOptions | IEditorGroup | GroupIdentifier | SIDE_GROUP_TYPE | ACTIVE_GROUP_TYPE, group?: GroupIdentifier): Promise<IEditor> {
+	openEditor(editor: IEditorInput, options?: IEditorOptions | ITextEditorOptions, group?: IEditorGroup | GroupIdentifier | SIDE_GROUP_TYPE | ACTIVE_GROUP_TYPE): Promise<IEditor | null>;
+	openEditor(editor: IResourceInput | IUntitledResourceInput, group?: IEditorGroup | GroupIdentifier | SIDE_GROUP_TYPE | ACTIVE_GROUP_TYPE): Promise<ITextEditor | null>;
+	openEditor(editor: IResourceDiffInput, group?: IEditorGroup | GroupIdentifier | SIDE_GROUP_TYPE | ACTIVE_GROUP_TYPE): Promise<ITextDiffEditor | null>;
+	openEditor(editor: IResourceSideBySideInput, group?: IEditorGroup | GroupIdentifier | SIDE_GROUP_TYPE | ACTIVE_GROUP_TYPE): Promise<ITextSideBySideEditor | null>;
+	openEditor(editor: IEditorInput | IResourceEditor, optionsOrGroup?: IEditorOptions | ITextEditorOptions | IEditorGroup | GroupIdentifier | SIDE_GROUP_TYPE | ACTIVE_GROUP_TYPE, group?: GroupIdentifier): Promise<IEditor | null> {
 
 		// Typed Editor Support
 		if (editor instanceof EditorInput) {
@@ -241,7 +241,7 @@ export class EditorService extends Disposable implements EditorServiceImpl {
 		return Promise.resolve(null);
 	}
 
-	protected doOpenEditor(group: IEditorGroup, editor: IEditorInput, options?: IEditorOptions): Promise<IEditor> {
+	protected doOpenEditor(group: IEditorGroup, editor: IEditorInput, options?: IEditorOptions): Promise<IEditor | null> {
 		return group.openEditor(editor, options);
 	}
 

src/vs/workbench/services/editor/common/editorService.ts

@@ -119,10 +119,10 @@ export interface IEditorService {
 	 * @returns the editor that opened or NULL if the operation failed or the editor was not
 	 * opened to be active.
 	 */
-	openEditor(editor: IEditorInput, options?: IEditorOptions | ITextEditorOptions, group?: IEditorGroup | GroupIdentifier | SIDE_GROUP_TYPE | ACTIVE_GROUP_TYPE): Promise<IEditor>;
-	openEditor(editor: IResourceInput | IUntitledResourceInput, group?: IEditorGroup | GroupIdentifier | SIDE_GROUP_TYPE | ACTIVE_GROUP_TYPE): Promise<ITextEditor>;
-	openEditor(editor: IResourceDiffInput, group?: IEditorGroup | GroupIdentifier | SIDE_GROUP_TYPE | ACTIVE_GROUP_TYPE): Promise<ITextDiffEditor>;
-	openEditor(editor: IResourceSideBySideInput, group?: IEditorGroup | GroupIdentifier | SIDE_GROUP_TYPE | ACTIVE_GROUP_TYPE): Promise<ITextSideBySideEditor>;
+	openEditor(editor: IEditorInput, options?: IEditorOptions | ITextEditorOptions, group?: IEditorGroup | GroupIdentifier | SIDE_GROUP_TYPE | ACTIVE_GROUP_TYPE): Promise<IEditor | null>;
+	openEditor(editor: IResourceInput | IUntitledResourceInput, group?: IEditorGroup | GroupIdentifier | SIDE_GROUP_TYPE | ACTIVE_GROUP_TYPE): Promise<ITextEditor | null>;
+	openEditor(editor: IResourceDiffInput, group?: IEditorGroup | GroupIdentifier | SIDE_GROUP_TYPE | ACTIVE_GROUP_TYPE): Promise<ITextDiffEditor | null>;
+	openEditor(editor: IResourceSideBySideInput, group?: IEditorGroup | GroupIdentifier | SIDE_GROUP_TYPE | ACTIVE_GROUP_TYPE): Promise<ITextSideBySideEditor | null>;
 
 	/**
 	 * Open editors in an editor group.

src/vs/workbench/services/history/browser/history.ts

@@ -420,7 +420,7 @@ export class HistoryService extends Disposable implements IHistoryService {
 		this.doNavigate(this.stack[this.index], !acrossEditors).finally(() => this.navigatingInStack = false);
 	}
 
-	private doNavigate(location: IStackEntry, withSelection: boolean): Promise<IBaseEditor> {
+	private doNavigate(location: IStackEntry, withSelection: boolean): Promise<IBaseEditor | null> {
 		const options: ITextEditorOptions = {
 			revealIfOpened: true // support to navigate across editor groups
 		};