debug: better error handling when 'type' missing

fixes #3343

src/vs/workbench/parts/debug/electron-browser/debugService.ts

@@ -522,7 +522,9 @@ export class DebugService extends ee.EventEmitter implements debug.IDebugService
 			}
 			if (!this.configurationManager.getAdapter()) {
 				this.emit(debug.ServiceEvents.TYPE_NOT_SUPPORTED, configuration.type);
-				return TPromise.wrapError(new Error(nls.localize('debugTypeNotSupported', "Configured debug type '{0}' is not supported.", configuration.type)));
+				return configuration.type ? TPromise.wrapError(new Error(nls.localize('debugTypeNotSupported', "Configured debug type '{0}' is not supported.", configuration.type)))
+					: TPromise.wrapError(errors.create(nls.localize('debugTypeMissing', "Missing property 'type' for the selected configuration in launch.json."),
+						{ actions: [CloseAction, this.instantiationService.createInstance(debugactions.ConfigureAction, debugactions.ConfigureAction.ID, debugactions.ConfigureAction.LABEL)] }));
 			}
 
 			return this.runPreLaunchTask(configuration.preLaunchTask).then((taskSummary: ITaskSummary) => {