G'MIC flatpak plugin vanished from flatpak GIMP 2.10.24

I am using GIMP 2.10.24 (Flatpak) on Ubuntu 18.04. I have been using the GMIC flatpak plugin with GIMP for many months.

After a recent flatpak update, the G’MIC plugin has stopped appearing in the GIMP Filters menu. No change made to GIMP config or any other disk configuration so I think the flatpak or OS update caused it, but I may be wrong.

I checked if the flatpak gmic plugin is installed using ‘flatpak search org.gimp.GIMP.Plugin’. It shows the gmic plugin is installed along with six other plugins like resynthesizer, liquid rescale etc. So my guess is that the folders list of GIMP preferences is not pointing to the right flatpak plugin folder causing the plugin to vanish from GIMP. So the question is where do flatpak GIMP plugins reside?

Also, there is a (new??) column listed by flatpak showing ‘branch’ (2-3.36 / 2-40) for each plugin installed. What does it indicate ?

I think you need to remove the 3.36 version of the G’MIC plugin and install the 40 version. At least for me the flatpak system didn’t made this update automatically.

Edit: I guess the ‘branch’ refers to the Gnome runtime needed, the latest GIMP depends on Gnome 40, the previous on Gnome 3.36

Update: I just reinstalled flatpak and the plugin has now re-appeared in GIMP.
Not happy though because couldn’t determine what exactly was wrong. Need to do some serious research…

Perhaps @Jehan or @David_Tschumperle can help here.

Indeed this is the reason. Basically when we update the runtime (i.e. the dependencies), the plug-ins have to be rebuilt. It may not be always true, but sometimes it’s mandatory because of how binary linking work.

See the comment about the main maintainer of these plug-in packages: https://github.com/flathub/org.gimp.GIMP/pull/98#issuecomment-808351795

In particular this sentence:

Yes it’s better. But two things: if you don’t change the extension version in the extension point, they should work: it combine the Gimp API (2) and the Runtime versions (40). Between two Gnome runtimes on the same freedesktop, it should be ok. 42 will likely be based on 21.08 though, which is the biggest leap: new glib, new compiler, etc.

Basically when the plug-ins need to be rebuilt, a new branch will be created in GIMP’s manifest, with the version scheme managed by Hubert Figuière: https://github.com/flathub/org.gimp.GIMP/blob/master/org.gimp.GIMP.json#L45

Then plug-ins will also have to update to the same base SDK and set this new branch, for instance in G’MIC: https://github.com/flathub/org.gimp.GIMP.Plugin.GMic/blob/master/org.gimp.GIMP.Plugin.GMic.json#L3

That’s for the technical part. Now I agree that non-dev should not have to dig into such technicalities. It’s annoying indeed if flatpak is not able to switch to the new extension branch (hence propose to update installed extensions from the new branch) as it has all the info. I wil discuss with Hubert to be sure we get all the technicalities right so that we can make a feature request to flatpak.

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Thank you @guille2306 @Jehan @Tobias.
This is certainly too technical for me, but it surely gives me a direction for doing more research.

For the record, a feature request/bug report has been opened so that flatpak becomes able to update plug-ins when we bump the runtime: https://github.com/flatpak/flatpak/issues/4208

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