resolve document when running document sumbol command

src/vs/editor/contrib/quickOpen/quickOpen.ts

@@ -11,6 +11,7 @@ import { registerLanguageCommand } from 'vs/editor/browser/editorExtensions';
 import { DocumentSymbol, DocumentSymbolProviderRegistry } from 'vs/editor/common/modes';
 import { IModelService } from 'vs/editor/common/services/modelService';
 import { CancellationToken } from 'vs/base/common/cancellation';
+import { ITextModelService } from 'vs/editor/common/services/resolverService';
 
 export function getDocumentSymbols(model: ITextModel, flat: boolean, token: CancellationToken): Promise<DocumentSymbol[]> {
 
@@ -70,8 +71,20 @@ registerLanguageCommand('_executeDocumentSymbolProvider', function (accessor, ar
 		throw illegalArgument('resource');
 	}
 	const model = accessor.get(IModelService).getModel(resource);
-	if (!model) {
-		throw illegalArgument('resource');
+	if (model) {
+		return getDocumentSymbols(model, false, CancellationToken.None);
 	}
-	return getDocumentSymbols(model, false, CancellationToken.None);
+
+	return accessor.get(ITextModelService).createModelReference(resource).then(reference => {
+		return new Promise((resolve, reject) => {
+			try {
+				const result = getDocumentSymbols(model, false, CancellationToken.None);
+				resolve(result);
+			} catch (err) {
+				reject(err);
+			}
+		}).finally(() => {
+			reference.dispose();
+		});
+	});
 });