Creating a new document with UIDocumentBrowserViewControllerDelegate (from Document Based App template)

I created a new app in Xcode 11.2 based off the iOS Document Based app template. I then modified the document type to a custom type, and made a small change to use a file in the bundle as a template when making a new document. I left the rest of the default boilerplate alone. I tried building the app (both with an iPhone and iPad target) and tried to create a new app. Nothing happens, no errors are raised, and the delegate function didRequestDocumentCreationWithHandler is not called (I added a print statement as the first line to make sure). Why is this? What did I change to break this?

Of interesting note, before making any changes, after building, the "browse" pane of the document view had an icon for "Create Document" (a blank square with a plus in the middle), but after making changes, that and the folder name have both vanished (Broken | Expected):

I suspect the error is something subtle in my info.plist:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <key>CFBundleDevelopmentRegion</key>
    <string>$(DEVELOPMENT_LANGUAGE)</string>
    <key>CFBundleDocumentTypes</key>
    <array>
        <dict>
            <key>CFBundleTypeIconFiles</key>
            <array/>
            <key>CFBundleTypeName</key>
            <string>Lifreyan Layout</string>
            <key>CFBundleTypeRole</key>
            <string>Editor</string>
            <key>LSHandlerRank</key>
            <string>Owner</string>
            <key>LSItemContentTypes</key>
            <array>
                <string>name.cableray.lifreyanlayout</string>
            </array>
        </dict>
    </array>
    <key>CFBundleExecutable</key>
    <string>$(EXECUTABLE_NAME)</string>
    <key>CFBundleIdentifier</key>
    <string>$(PRODUCT_BUNDLE_IDENTIFIER)</string>
    <key>CFBundleInfoDictionaryVersion</key>
    <string>6.0</string>
    <key>CFBundleName</key>
    <string>$(PRODUCT_NAME)</string>
    <key>CFBundlePackageType</key>
    <string>$(PRODUCT_BUNDLE_PACKAGE_TYPE)</string>
    <key>CFBundleShortVersionString</key>
    <string>1.0</string>
    <key>CFBundleVersion</key>
    <string>1</string>
    <key>LSRequiresIPhoneOS</key>
    <true/>
    <key>UILaunchStoryboardName</key>
    <string>LaunchScreen</string>
    <key>UIMainStoryboardFile</key>
    <string>Main</string>
    <key>UIRequiredDeviceCapabilities</key>
    <array>
        <string>armv7</string>
    </array>
    <key>UISupportedInterfaceOrientations</key>
    <array>
        <string>UIInterfaceOrientationPortrait</string>
        <string>UIInterfaceOrientationLandscapeLeft</string>
        <string>UIInterfaceOrientationLandscapeRight</string>
    </array>
    <key>UISupportedInterfaceOrientations~ipad</key>
    <array>
        <string>UIInterfaceOrientationPortrait</string>
        <string>UIInterfaceOrientationPortraitUpsideDown</string>
        <string>UIInterfaceOrientationLandscapeLeft</string>
        <string>UIInterfaceOrientationLandscapeRight</string>
    </array>
    <key>UISupportsDocumentBrowser</key>
    <true/>
    <key>UTExportedTypeDeclarations</key>
    <array>
        <dict>
            <key>UTTypeDescription</key>
            <string>Lifreyan Script Layout</string>
            <key>UTTypeIconFiles</key>
            <array/>
            <key>UTTypeIdentifier</key>
            <string>name.cableray.lifreyanlayout</string>
            <key>UTTypeTagSpecification</key>
            <dict>
                <key>public.filename-extension</key>
                <string>lifreyanlayout</string>
                <key>public.mime-type</key>
                <string>name.cableray.lifreyanlayout</string>
            </dict>
        </dict>
    </array>
    <key>UTImportedTypeDeclarations</key>
    <array/>
</dict>
</plist>

Just in case, my Document Browser Delegate:

import UIKit
import SwiftUI

class DocumentBrowserViewController: UIDocumentBrowserViewController, UIDocumentBrowserViewControllerDelegate {

    override func viewDidLoad() {
        super.viewDidLoad()

        delegate = self

        allowsDocumentCreation = true
        allowsPickingMultipleItems = false
    }


    // MARK: UIDocumentBrowserViewControllerDelegate

    func documentBrowser(_ controller: UIDocumentBrowserViewController, didRequestDocumentCreationWithHandler importHandler: @escaping (URL?, UIDocumentBrowserViewController.ImportMode) -> Void) {
        print("importing new")
        let newDocumentURL = Bundle.main.url(forResource: "Default", withExtension: "lifreyanlayout")

        // Set the URL for the new document here. Optionally, you can present a template chooser before calling the importHandler.
        // Make sure the importHandler is always called, even if the user cancels the creation request.
        if newDocumentURL != nil {
            importHandler(newDocumentURL, .copy)
        } else {
            importHandler(nil, .none)
        }
    }

    func documentBrowser(_ controller: UIDocumentBrowserViewController, didPickDocumentsAt documentURLs: [URL]) {
        guard let sourceURL = documentURLs.first else { return }

        // Present the Document View Controller for the first document that was picked.
        // If you support picking multiple items, make sure you handle them all.
        presentDocument(at: sourceURL)
    }

    func documentBrowser(_ controller: UIDocumentBrowserViewController, didImportDocumentAt sourceURL: URL, toDestinationURL destinationURL: URL) {
        // Present the Document View Controller for the new newly created document
        presentDocument(at: destinationURL)
    }

    func documentBrowser(_ controller: UIDocumentBrowserViewController, failedToImportDocumentAt documentURL: URL, error: Error?) {
        // Make sure to handle the failed import appropriately, e.g., by presenting an error message to the user.
    }

    // MARK: Document Presentation

    func presentDocument(at documentURL: URL) {
        let document = Document(fileURL: documentURL)

        // Access the document
        document.open(completionHandler: { success in
            if success {
                // Display the content of the document:
                let view = DocumentView(document: document, dismiss: {
                    self.closeDocument(document)
                })

                let documentViewController = UIHostingController(rootView: view)
                self.present(documentViewController, animated: true, completion: nil)
            } else {
                // Make sure to handle the failed import appropriately, e.g., by presenting an error message to the user.
            }
        })
    }

    func closeDocument(_ document: Document) {
        dismiss(animated: true) {
            document.close(completionHandler: nil)
        }
    }
}

I've compared my project with working examples, and can't find any major differences...

I determined the issue: Custom UTIs must (it appears) specify a conforming type that descends from either public.data or com.apple.package.

So adding this to the UTI worked:

    <key>UTTypeConformsTo</key>
    <array>
        <string>public.data</string>
    </array>

References:

• Declaring New Uniform Type Identifiers
• System-Declared Uniform Type Identifiers