src/vs/workbench/api/common/extHostQuickOpen.ts/ExtHostQuickOpenImpl/$validateInput
class ExtHostQuickOpenImpl:		async $validateInput(input: string): Promise<string | { content: string; severity: Severity } | null | undefined> {
			if (!this._validateInput) {
				return;
			}

			const result = await this._validateInput(input);
			if (!result || typeof result === 'string') {
				return result;
			}

			let severity: Severity;
			switch (result.severity) {
				case InputBoxValidationSeverity.Info:
					severity = Severity.Info;
					break;
				case InputBoxValidationSeverity.Warning:
					severity = Severity.Warning;
					break;
				case InputBoxValidationSeverity.Error:
					severity = Severity.Error;
					break;
				default:
					severity = result.message ? Severity.Error : Severity.Ignore;
					break;
			}

			return {
				content: result.message,
				severity
			};
		}