fixes #4419

src/vs/workbench/browser/actions/triggerEditorActions.ts

@@ -336,7 +336,7 @@ export class OpenToSideAction extends Action {
 	public static OPEN_TO_SIDE_ID = 'workbench.action.openToSide';
 	public static OPEN_TO_SIDE_LABEL = nls.localize('openToSide', "Open to the Side");
 
-	constructor( @IWorkbenchEditorService private editorService: IWorkbenchEditorService) {
+	constructor(@IWorkbenchEditorService private editorService: IWorkbenchEditorService) {
 		super(OpenToSideAction.OPEN_TO_SIDE_ID, OpenToSideAction.OPEN_TO_SIDE_LABEL);
 
 		this.class = 'quick-open-sidebyside';
@@ -352,7 +352,15 @@ export class OpenToSideAction extends Action {
 	public run(context: any): TPromise<any> {
 		let entry = toEditorQuickOpenEntry(context);
 		if (entry) {
-			return this.editorService.openEditor(<EditorInput>entry.getInput(), entry.getOptions(), true);
+			let typedInputPromise: TPromise<EditorInput>;
+			let input = entry.getInput();
+			if (input instanceof EditorInput) {
+				typedInputPromise = TPromise.as(input);
+			} else {
+				typedInputPromise = this.editorService.inputToType(input);
+			}
+
+			return typedInputPromise.then(typedInput => this.editorService.openEditor(typedInput, entry.getOptions(), true));
 		}
 
 		return TPromise.as(false);