add command to repair broken filesystem trees

[icewind1991]

If for any reason the path of an entry in the filecache doesn't match with it's expected path based on the path of it's parent node you end up with an entry in the filecache that exists in different places based on how the entry is generated. For example, while listing folder /foo is contains a file bar.txt, but when trying to do anything with /foo/bar.txt the file doesn't exists.

This command attempts to repair such entries by querying for entries there the path doesn't match the expected path based on it's parent path and filename and resets it's path to the expected one.

It is not guaranteed that the "new" path is the correct one, but while that would leave the filecache and actual filesystem out of sync, various automated and manual processes to fix that already exist as filecache synchronization is a much wider topic.
By comparison there isn't currently any way (short of manual database editing) to repair a broken file tree.

[rullzer]

Makes sense
But I didn't test it. Is there an easy way to test it?

[icewind1991]

you can manually break your filesystem tree by changing the path and path_hash of a filesystem entry without changing the parent

[nickvergessen]

Looks good

[ChristophWurst]

Code makes sense as far as I understand the file cache

👍 (🐘)

[PVince81]

would be good to have unit tests to confirm that this isn't causing any side effects

something like https://github.com/owncloud/core/pull/28253/files#diff-61c2bd81935832b24f87e329f7b6374aa736b3d7c74196581abe0892d983303e

[icewind1991]

/backport to stable20

[icewind1991]

/backport to stable19