Improve Icon Theme Loading Error Communication

[Kreevoz]

Having spent 3 hours getting to the bottom of why my labwc install refused to show any icons in all menus, and finding no information about this on the internet, I'd like to both document this here so that others may save time, and also raise this issue as something that poorly communicates to the user what is going on, and should/could be improved.

The other discussions pertaining to missing icons did not indicate a total fail of this subsystem, so the matter here is different.

Take this case:

• A user has one or more (icon-)themes from various sources, which have a malformed / corrupt / invalid index.theme file.
• The user is not using this theme as their active theme.
  Other applications do not get bothered by the broken theme since they have no business in dealing with it. So there are no other problems on the system.

Unlike other applications, labwc very much deals with this corrupt inactive theme.
Labwc uses libsfdo to do the heavy lifting of looking for the xdg user folders, and apparently also validating the available themes therein.

• libsfdo loads up every single index.theme file it finds in those folders. The moment it runs across a file that is not valid, it completely stops working and throws an error, and returns NULL ! ( libsfdo/sfdo-basedir/basedir.c )
• This error trips up labwc which then no longer gets any information about the themes, stops trying to initialize the icon module, and gives up immediately.

The only hint at what is going on would be a system journal entry like this:
Oct 07 07:37:02 grid10 uwsm_labwc[138746]: 00:00:00.159 [ERROR] [../labwc/src/desktop-entry.c:131] Failed to initialize icon loader

• Only by turning on verbose debugging and setting the environment variable LABWC_DEBUG_LIBSFDO does the broken index.theme file and the offending theme get identified, and listed in the log output.

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That a single file in an inactive icon theme can break labwc's icon display is unfortunate from a user perspective.
It is not your fault, yet you're the only project (that I'm aware of) which uses libsfdo for this purpose.

🙏 Could you possibly alter the error message you're emitting into the system journal?

Simply telling the user what happened, that they might have a corrupt theme, and that they should delete all their custom themes or something along those lines would be a huge improvement.

Alternatively perhaps you could consider not letting libsfdo touch any inactive theme files, or make this portion of your code more robust, maybe with a simple fallback that does a last-resort hard-coded loading of Adwaita or somesuch, while emitting a warning into the log.

Just wanted to bring this to your attention, I'm enjoying labwc greatly so thanks for your hard work! 😁

[Consolatis]

Sorry what you've gone through to diagnose the actual issue. And thanks for sharing your experience here!

It sounds like something we could bring up at libsfdo, failure to parse a theme should not prevent all other themes to be parsed.
Could you share that broken index.theme file so we can reproduce the issue and see if there is some better way to handle the situation?

[tokyo4j]

• A user has one or more (icon-)themes from various sources, which have a malformed / corrupt / invalid index.theme file.
• The user is not using this theme as their active theme.

Could you elaborate on "various sources"? Which index.theme is broken in your case?

[Kreevoz]

Of course, yes. Sorry, I forgot about reproducability - didn't mean to make it sound more mysterious than it is and did not want to put blame on a single theme pack. 😅

Download the zip file of this theme's master branch here: https://github.com/B00merang-Artwork/Windows-XP
Unzip it and move it onto ~/.local/share/icons. You don't have to pick it as active theme or do anything to it. Just restart labwc.

[tokyo4j]

Thanks, I reproduced the issue.

I filed a MR in libsfdo to allow falling back to hicolor theme when the specified theme is invalid: https://gitlab.freedesktop.org/vyivel/libsfdo/-/merge_requests/12

[Consolatis]

Thanks, I reproduced the issue.

I couldn't actually reproduce it on a quick try yesterday. Did git clone the theme repo into ~/.local/share/icons, set LABWC_DEBUG_LIBSFDO and started nested. the theme wasn't mentioned in the log at all and the app-icons were loaded from my configured icon theme (Numix) as usual.

[Consolatis]

Alright, when selecting the icon theme manually (via <theme icon="Windows-XP" />) the issue shows up. Additionally to the libsfdo MR I prepared #3129 to fix it on the labwc side for now. That allows to ship the fix before we can rely on a new libsfdo version being released.

Testing appreciated.

[Consolatis]

Thanks for the report. Should be fixed on the master branch (and therefore the upcoming release).