hook_icon_pack_alter() is undocumented

Hey @kanchanandhini6 that's awesome, sure thing! Feel free to assign the issue to yourself.

Some pointers that hopefully help:

• Since the Icon API is not part of a module, but part of the core theming system, the hook should be documented in the core.api.php file
• You can find a few plugin definition alter hooks in there, to model your hook after. hook_validation_constraint_alter() for example. Even though it's a completely different part of core, the hook documentation should look somewhat similar.
• I don't think this is a hard requirement, so if you're stuck on this just go ahead and push the code without this, but ideally it would be nice to use this hook to document the structure of the icon pack definition array because that does not exist anywhere as far as I can tell. For that you can check out navigation.icons.yml, to see which keys are available. As a reference for how such an array can be documented, take a look at \Drupal\Core\Asset\LibraryDiscoveryParser::parseLibraryInfo(). But again, feel free to ignore this point for now if it's a bit too much or bit too confusing.

Let me know if there's anything else that's unclear or if you need help with the contribution workflow in general.

I don't see any issue branch (or an issue fork where that branch would live, for that matter). Can you point me to where you pushed the code?

Re #9: See \Drupal\Core\Theme\Icon\Plugin\IconPackManager::__construct(). Through the use of $this->alterInfo() hook_icon_pack_alter() will be called during plugin discovery automatically. Yeah, the @see is a bit unfortunate without further explanation, I agree, so I'd vote to remove that as well, for now.

Will do a detailed code review now.

Opened #3572674: Allow themes to call hook_icon_pack_alter() for the follow-up.

Awesome, thanks for the quick follow-up @kanchanandhini6! Looks perfect now and PHPCS is happy as well. I think it's good to go.

Good question @nicxvan. I totally didn't know theme.api.php exists. I took a look whether that only contains hooks that are actually invoked in themes vs. just being generally theme related, but that's not the case. For example hook_library_info_build() is documented there, which is only for modules. hook_icon_pack_alter() seems similar enough in that it's theme or rendering related. So I would say, yes, let's move it to theme.api.php (that's in core/lib/Drupal/Core/Render, regardless of the outcome of #3572674: Allow themes to call hook_icon_pack_alter().

Marking needs work for that, are you up for moving the documentation over to the other file @kanchanandhini6?

@kanchanandhini6 thanks for the quick response, awesome!

One tiny thing: in theme.api.php the new hook is now outside of the "hook" documentation group, so if you could move it up to be inside of that, that would be perfect.

Awesome, thanks, looks great!