Workaround cleanup of the folder marker by Huawei, Xiaomi firmware (fixes #131)

[Catfriend1]

Purpose:

• Create .stfolder and DO_NOT_DELETE.txt within it to prevent automatic cleanup of empty directories (fixes Create .stfolder and DO_NOT_DELETE.txt within it to prevent automatic cleanup of empty directories #131)
• This is a workaround for phones running manufacturer specific cleanup tools in the background.

Testing:

• Verified doing technically the right thing on AVD 9.x at commit 99e1659 .
• Needs community test.

[Catfriend1]

@Review/Complete
lgtm.

[Catfriend1]

Anyone having the same issue reading this? I've put up a test APK at https://drive.google.com/open?id=1FyPl16VXL6WAjuazSDIBtaN79ZRCTX0o and would appreciate feedback if this works correctly after adding a new folder and running the phone's file cleanup utility. The workaround adds a dummy text file below the ".stfolder" directory.

[otbutz]

@Catfriend1 i don't have a phone which is affected but it might be worth to run a public beta test on the PlayStore for things like this

[GottZ]

what about already existing sync folders where the .stfolder has been deleted already?
i doubt users know what to do when they see the "folder marker missing" error.

[GottZ]

hereby confirm this works on my Huawei Mate 10 Pro

[Catfriend1]

Thanks for reporting back. Already missing markers have to be restored manually as it would circumvent the safety meaning of why the marker exists when we would recreate it automatically.