Open Radar

 
How to duplicate the issue:

(1) On a device running iOS 15.5 or iPadOS 15.5, try opening an attachment via Apple Mail whose document type is a custom type (whose app is installed on the device).

(2) If the app's Document Storage setting in the Settings app is set to local storage ("On My iPad" or "On My iPhone"), the document fails to be imported into the app.  Any call to the UIDocumentBrowserViewController's revealDocument(at:importIfNeeded:completion:) method [initiated from either the appDelegate's application(_:open:options:) method or the sceneDelegate's scene(_:openURLContexts:) method] returns nil for both parameters of the completion handler, the error parameter and the revealedDocumentURL parameter.  In addition, the UIDocumentBrowserViewController's documentBrowser(_:failedToImportDocumentAt:error:) method is called, but returns nil for its error.  

What should happen instead:  
the Mail attachment *should* be imported into its app.

An additional piece of info: if the app's Document Storage setting in the Settings app is instead set to "iCloud Drive," the Mail attachment *is* properly imported.


The issue can be duplicated using Apple's own UIDocumentBrowserViewController "Particles" app sample code (downloaded from https://developer.apple.com/documentation/uikit/view_controllers/building_a_document_browser_app_for_custom_file_formats), unmodified.