src/vs/base/common/errorMessage.ts/toErrorMessage
export function toErrorMessage(error: any = null, verbose: boolean = false): string {
	if (!error) {
		return nls.localize('error.defaultMessage', "An unknown error occurred. Please consult the log for more details.");
	}

	if (Array.isArray(error)) {
		const errors: any[] = arrays.coalesce(error);
		const msg = toErrorMessage(errors[0], verbose);

		if (errors.length > 1) {
			return nls.localize('error.moreErrors', "{0} ({1} errors in total)", msg, errors.length);
		}

		return msg;
	}

	if (types.isString(error)) {
		return error;
	}

	if (error.detail) {
		const detail = error.detail;

		if (detail.error) {
			return exceptionToErrorMessage(detail.error, verbose);
		}

		if (detail.exception) {
			return exceptionToErrorMessage(detail.exception, verbose);
		}
	}

	if (error.stack) {
		return exceptionToErrorMessage(error, verbose);
	}

	if (error.message) {
		return error.message;
	}

	return nls.localize('error.defaultMessage', "An unknown error occurred. Please consult the log for more details.");
}