Ghost files in cache due to fast operations

[faulix]

Steps to reproduce

0. Use the client app for synchronization
1. Copy a synchronized folder locally (gets copied with prefix "copy of" or similar)
2. Rename the folder quickly

Expected behaviour

The final folder should be synchronized, the interim versions should be deleted.

Actual behaviour

Ghost files occur, as the interim files are created in the filecache, but no files exist on the harddisk.

Server configuration

PHP version: 7

Nextcloud version: 12.0.0

Problem tracking

I think the problem occurs when a file gets updated locally while the file synchronization runs. The upload of the file seems to abort, but there is no cache rollback as the entry is already created (assumption).

[LukasReschke]

cc @icewind1991

[faulix]

I should also mention that neither occ files:cleanup nor occ files:scan delete the ghost files

[MorrisJobke]

Looks like a duplicate of #741

Let's continue there.