File extensions for specified UTType and all its descenders

fileExtensionsForUTType.swift

import UniformTypeIdentifiers

let allTypes: [UTType] = [
    .item,
    .content,
    .compositeContent,
    .diskImage,
    .data,
    .directory,
    .resolvable,
    .symbolicLink,
    .executable,
    .mountPoint,
    .aliasFile,
    .urlBookmarkData,
    .url,
    .fileURL,
    .text,
    .plainText,
    .utf8PlainText,
    .utf16ExternalPlainText,
    .utf16PlainText,
    .delimitedText,
    .commaSeparatedText,
    .tabSeparatedText,
    .utf8TabSeparatedText,
    .rtf,
    .html,
    .xml,
    .yaml,
    .sourceCode,
    .assemblyLanguageSource,
    .cSource,
    .objectiveCSource,
    .swiftSource,
    .cPlusPlusSource,
    .objectiveCPlusPlusSource,
    .cHeader,
    .cPlusPlusHeader,
    .script,
    .appleScript,
    .osaScript,
    .osaScriptBundle,
    .javaScript,
    .shellScript,
    .perlScript,
    .pythonScript,
    .rubyScript,
    .phpScript,
    .makefile,
    .json,
    .propertyList,
    .xmlPropertyList,
    .binaryPropertyList,
    .pdf,
    .rtfd,
    .flatRTFD,
    .webArchive,
    .image,
    .jpeg,
    .tiff,
    .gif,
    .png,
    .icns,
    .bmp,
    .ico,
    .rawImage,
    .svg,
    .livePhoto,
    .heif,
    .heic,
    .webP,
    .threeDContent,
    .usd,
    .usdz,
    .realityFile,
    .sceneKitScene,
    .arReferenceObject,
    .audiovisualContent,
    .movie,
    .video,
    .audio,
    .quickTimeMovie,
    .mpeg,
    .mpeg2Video,
    .mpeg2TransportStream,
    .mp3,
    .mpeg4Movie,
    .mpeg4Audio,
    .appleProtectedMPEG4Audio,
    .appleProtectedMPEG4Video,
    .avi,
    .aiff,
    .wav,
    .midi,
    .playlist,
    .m3uPlaylist,
    .folder,
    .volume,
    .package,
    .bundle,
    .pluginBundle,
    .spotlightImporter,
    .quickLookGenerator,
    .xpcService,
    .framework,
    .application,
    .applicationBundle,
    .applicationExtension,
    .unixExecutable,
    .exe,
    .systemPreferencesPane,
    .archive,
    .gzip,
    .bz2,
    .zip,
    .appleArchive,
    .spreadsheet,
    .presentation,
    .database,
    .message,
    .contact,
    .vCard,
    .toDoItem,
    .calendarEvent,
    .emailMessage,
    .internetLocation,
    .internetShortcut,
    .font,
    .bookmark,
    .pkcs12,
    .x509Certificate,
    .epub,
    .log
]

func fileExtensions(for type: UTType, level: Int = 0) -> [String] {
    // For debugging purpposes
    //let delimiter = String(repeating: " ", count: level)
    //print("\(delimiter)\(type)")
    var extensions = [String]()

    if let extensionsForSoleType = type.tags[.filenameExtension] {
        extensions.append(contentsOf: extensionsForSoleType)
    }

    allTypes.forEach { subtype in
        if subtype.isSubtype(of: type) {
            extensions.append(contentsOf: fileExtensions(for: subtype, level: level + 1))
        }
    }
    return extensions
}

print(fileExtensions(for: .text))