src/vs/workbench/api/common/extHostSCM.ts/ExtHostSCMInputBox/validateInput
class ExtHostSCMInputBox:	set validateInput(fn: IValidateInput | undefined) {
		checkProposedApiEnabled(this._extension, 'scmValidation');

		if (fn && typeof fn !== 'function') {
			throw new Error(`[${this._extension.identifier.value}]: Invalid SCM input box validation function`);
		}

		this._validateInput = fn;
		this.#proxy.$setValidationProviderIsEnabled(this._sourceControlHandle, !!fn);
	}