icon-theme-spec: clarify whether a theme listed in "Inherits" is required to exist

@ngraham: I think this is the root cause for all the trouble around adwaita-icon-theme.

Actually, adwaita-icon-theme specified to inherit from Tango (swapped now for AdwaitaLegacy) ... both do ship the icons which were removed from adwaita-icon-theme.

Though the meson.build file does not specify a dependency to Tango/AdwaitaLegacy to make sure it is available, and as such packagers don't implement this dependency either.

To me, it makes a lot of sense that if you want to use something as a base / inherit from something, than you need to make sure that it actually is available. Imo we should clearly write into the spec that a theme which makes use of Inherits, has to ensure that the themes to inherit from are installed.

Note that tango has a similar flaw. It inherits from the gnome and crystalsvg icon-themes, but does not specify the dependency in it's configure.ac. Using it as a base theme without having gnome/crystalsvg installed as well results in missing icons.

I did not further check for other themes.

Note that Tango was itself only added recently in https://gitlab.gnome.org/GNOME/adwaita-icon-theme/-/commit/788c7a2c0ff0b95d540148715c7cee612e9404f8 and was not present at the time https://gitlab.gnome.org/GNOME/adwaita-icon-theme/-/issues/288 was reported.

But yes, I agree that it's quite problematic for icon themes to specify fallback themes that aren't themselves guaranteed to be available.

I agree with the premise of the idea that inherited themes must be present or else it's a broken promise.

Note that Tango was itself only added recently

Uh, I missed that one.

Hmm, now that I re-test, it looks like gnome-icon-theme, not tango is the one which is used as fallback for missing Adwaita icons on my system. Thought that one is not even mentioned in Adwaitas index.theme … what a mess.

mentioned in merge request !5 (merged)

I can ask Alex (as I don't remember...), but I am pretty sure that it was always intended for the theme that another inherits from to exist. So this change makes a lot of sense to me, and is pretty much a bugfix.

If we would provide a default fallback theme from Freedesktop always, I think it would make sense to have that as a last-resort fallback theme all the time. But that's a change for later, once such a solution actually exists and the theme names have been revised.

In case anyone finds this interesting, I've opened the issue while I was writing an icon theme spec implementation and quite a few themes as provided by Fedora don't have their transitive dependencies installed (or packaged):

~/src/libsfdo $ build/examples/icon-lookup -R Numix 24 1 firefox
[error] Couldn't find an icon theme file for Breeze
Failed to load the icon theme
~/src/libsfdo $ build/examples/icon-lookup -R Moka 24 1 firefox
[error] Couldn't find an icon theme file for Faba
Failed to load the icon theme
~/src/libsfdo $ build/examples/icon-lookup -R Tango 24 1 firefox
[error] Couldn't find an icon theme file for crystalsvg
Failed to load the icon theme
~/src/libsfdo $ build/examples/icon-lookup -R Suru 24 1 firefox
[error] Couldn't find an icon theme file for Humanity
Failed to load the icon theme
~/src/libsfdo $ build/examples/icon-lookup -R La-Capitaine 24 1 firefox
[error] Couldn't find an icon theme file for deepin
Failed to load the icon theme

Given how lenient major implementations are about this, I presume the situation in other distros is similar.

Just had a chat about this issue with @clefebvre. He raised the idea that theme-pickers (like e.g. xfce4-appearance-settings) could show a warning for themes which define inherit themes which are not installed. Like that, the problem would become more attention.

An even more complete approach could be to check if all icons defined in the icon-naming-spec can be found by a theme. For that, a parsable list of fd.org supported icons would need to be added somewhere.

I suppose it would make sense to wait for the decision on xdg-specs#132 (comment 2409383) … if "hicolor" will be changed to be an ultimate backup theme, the script will not be needed. If not, I am willing to tinker a theme-validation script which can be added to the fd.org repo (or maybe libsfdo) and be used by every desktop-environment.

Edit: Created #26 for it.

mentioned in commit vyivel/libsfdo@7fba01ae

mentioned in commit cfaec5f3

closed