ResourceLoaderImageModule in MediaWiki already implements fallbacks like this. I guess this could still be a problem for other users of OOjs UI.

@matmarex When exactly does ResourceLoaderImageModule provide fallbacks? Which icons are necessary to backfill then?
Mass copying would simplify the task.

Related: T170329 (@matmarex expected fallback to work there)

Actually what I said isn't true, and never was, my mistake. It only does fallbacks to the default theme when the whole icon pack is missing, not when an icon pack exists but some icons in it are missing.

@matmarex Wouldn't it then be easier to remove certain icons, like for example userAvatar, which is exactly the same in WikimediaUI, from packs like icons-user in Apex instead of copying the rest?

@matmarex Also, are we sure that the fallback works as expected?

In T169890#3581967, @Volker_E wrote:

@matmarex Wouldn't it then be easier to remove certain icons, like for example userAvatar, which is exactly the same in WikimediaUI, from packs like icons-user in Apex instead of copying the rest?

Yeah, removing the incomplete packs would also work. Clever.

In T169890#3582021, @Volker_E wrote:

@matmarex Also, are we sure that the fallback works as expected?

The fallback for whole icon packs definitely works. For example, this gives you the expected CSS, even though the Apex theme (used by MonoBook skin) does not have the 'wikimedia' icon pack: https://en.wikipedia.org/w/load.php?debug=true&lang=en&modules=oojs-ui.styles.icons-wikimedia&skin=monobook&only=styles

@matmarex We would then probably have to figure something out about still showing Apex icons page with WikimediaUI icons in the demos (@Jdforrester-WMF is on the same page).
I don't think we will have the resources or the volunteers or a real strong need to provide special icons for Apex any soon future. We should rather focus our capacities on higher priority things.
The different icons I see in WikimediaUI vs Apex are

• indicators
  • Down, next, prev & up arrows
• interactions
  • check & clock (2 out of 23)
• moderation
  • lock, unlock, trash & untrash (4 out of 15)
• editing-core
  • link, redo & undo (3 out of 8)
• editing-list (4 out of 4)
• media
  • image & imageGallery (2 out of 7, 3 missing)

Packs with no difference:

• movement
• content (just a few in Apex missing)
• alert
• editing-styling
• editing-advanced
• location (all missing)
• user (all, but one missing)
• layout
• accessibility
• wikimedia

@Esanders How does this sound for you?

Sounds good. We should make sure the fallbacks work outside of MediaWiki too.

Although...

When we first created the two icon sets there were a lot more differences as the Wikimedia icons had been just been imported from a few sources and were full of inconsistencies that we have mostly ironed out now, in many cases by copying over from Apex. At this point there are so few differences between the packs I'm not sure it makes sense to maintain them both anymore.

@Esanders Yeah, I don't want to take away the few custom icons for now, because it could turn into an unnecessary discussion. If we update, I will revisit with the rest of the design team.

Change 397991 had a related patch set uploaded (by VolkerE; owner: VolkerE):
[oojs/ui@master] Apex theme: Remove duplicated icon packs

https://gerrit.wikimedia.org/r/397991

We've never had any issues with more significant icon changes in the past, and this wouldn't change that many icons. I think the best way forward is just to delete the apex icon set, and use wmui.

I'm fine with getting rid of the few extra icons and strongly guess other designers are with me. Do we think it might cause any irritation? (Most prominent to me seem to be the up/down indicators and the trash bin, probably the list icons).

Change 421781 had a related patch set uploaded (by Esanders; owner: Esanders):
[oojs/ui@master] Replace Apex icons set with WMUI icon set

https://gerrit.wikimedia.org/r/421781

Change 397991 abandoned by Jforrester:
Apex theme: Remove duplicated icon packs

Reason:
Doing in I0bda435ebef instead.

https://gerrit.wikimedia.org/r/397991

Change 421781 merged by jenkins-bot:
[oojs/ui@master] Apex icons: Replace entire set with WikimediaUI theme's

https://gerrit.wikimedia.org/r/421781