Small utility to check updates for flatpak installed apps.

This needs Python 3.5 or newer installed, and it uses the flatpak cli to get the information. It doesn't have any other external dependency.

$ ./flatpak-check-updates.py
com.github.xournalpp.xournalpp: 1.1.3 -> 1.1.3 [rebuild]
org.freedesktop.Platform.GL.default: 23.1.1 -> 21.3.9 [update]
org.freedesktop.Platform.VAAPI.Intel: [unknown]
org.freedesktop.Platform: 22.08.12.1 -> 21.08.18 [update]
org.gnome.Platform: [unknown]

Each app is "tagged" with a word,

• update: there's a new version of the app
• rebuild: there's an update available but the application version is the same as the locally installed one. This means that there was a change on the flatpak itself and the app was rebuilt, there's not a new version/release of the app.
• unknown: flatpak lists some apps with no version, I don't know what that means, possibly that they are not versioned with a number as other apps.

Where does the information come from?

This app/script basically gets the information from two Flatpak commands:

• flatpak remote-ls --updates: to list what has an update available
• flatpak list: to list the installed apps

From those two lists, I can show what's the current and new version for each and what's a rebuild instead of a new version.

At the time of writing this, there was not an official way of easily doing this.

See: flatpak/flatpak#729, flatpak/flatpak#985, flatpak/flatpak#3685