src/vs/workbench/api/common/extHostSCM.ts/ExtHostSCM/$validateInput
class ExtHostSCM:	$validateInput(sourceControlHandle: number, value: string, cursorPosition: number): Promise<[string | IMarkdownString, number] | undefined> {
		this.logService.trace('ExtHostSCM#$validateInput', sourceControlHandle);

		const sourceControl = this._sourceControls.get(sourceControlHandle);

		if (!sourceControl) {
			return Promise.resolve(undefined);
		}

		if (!sourceControl.inputBox.validateInput) {
			return Promise.resolve(undefined);
		}

		return asPromise(() => sourceControl.inputBox.validateInput!(value, cursorPosition)).then(result => {
			if (!result) {
				return Promise.resolve(undefined);
			}

			const message = MarkdownString.fromStrict(result.message);
			if (!message) {
				return Promise.resolve(undefined);
			}

			return Promise.resolve<[string | IMarkdownString, number]>([message, result.type]);
		});
	}