Sorry for the lack of time to do a proper review.

I will need to have a thorough look at what Elisa is currently doing and what is working (or not).

Is there another working way to get information about files that have moved without having an application monitor them itself ?

If I remember correctly, Baloo is not providing information about that even though it is monitoring it. Is this still the case ?

The unusual method to get notified is about avoiding signaling moved files if nobody is watching. Baloo will only callback if applications have registered themselves.

In D28980#652087, @mgallien wrote:

The unusual method to get notified is about avoiding signaling moved files if nobody is watching. Baloo will only callback if applications have registered themselves.

Registering for (expensive) notifications is fine, the org.kde.baloo.fileindexer interface is doing it as well the awkward part is
a) using a method call instead of a signal
b) registering an interface to be called, instead of just a service name

In D28980#652102, @mgallien wrote:

To be clear, I am fine with this change going in.

I would still like to work on a proper solution to allow an application to monitor moved files or similar stuff without having to add file system watchers itself (duplicate from Baloo owns watchers).

Do you have an idea ?

Elisa would need to register something like a "persistent query". This is something also dolphin needs - there definitely already is some notification between dolphin/baloo, but that is not working properly.

This could be something like "Audio files in ~/Music/", "Audio files in ~/Audio books/", etc., and you get a signal whenever the query would return a different result.

In D28980#652256, @bruns wrote:

In D28980#652102, @mgallien wrote:

To be clear, I am fine with this change going in.

I would still like to work on a proper solution to allow an application to monitor moved files or similar stuff without having to add file system watchers itself (duplicate from Baloo owns watchers).

Do you have an idea ?

Elisa would need to register something like a "persistent query". This is something also dolphin needs - there definitely already is some notification between dolphin/baloo, but that is not working properly.

This could be something like "Audio files in ~/Music/", "Audio files in ~/Audio books/", etc., and you get a signal whenever the query would return a different result.

That solution would be perfect and rely on working code inside Elisa.

Do you plan to work on it or should I start working on that ? That could take several weeks to be done.