feat(mentions,tags): tag mentions

[SychO9]

Also Closes #3725
Also Closes #3693

Changes proposed in this pull request:

• Refactors JS autocomplete code to allow easily adding different mention formats and different mentionable models. Notably, we now have the interfaces MentionableModel and MentionFormat.
• Adds tags search on the tags API list endpoint.
• Adds tag mentions tests.
• Adds a tag mention feature using the format: #slug since the slug is unique.
• Adds tag mention stying.
• Fixes unauthorized mention of hidden groups.
• Makes sure the mentions extension works with and without the tags extension installed/enabled.

Reviewers should focus on:

• The actual post_mentions_tag table migration resides i the tags extension whereas the rest of the tag mention logic resides in the mentions extension. This is done for the following reasons:
  • It shouldn't matter because by 2.0 we will have a polymorphic backend implementation of mentionable models, in which case this table will be dropped anyway.
  • Even if the mentions extension isn't used, the existence of the table does not add inconvenience.
  • There is a very good chance we will use this table to fix ([Tags] Event posts reference [Deleted] tag issue-archive#44) as part of tags anyway, in which case it would make sense to have it in tags.
• The mentions extension introduces an extension API to easily add new mention formats and new mentionable models, for example, if I was building a discussion mention extension that used a format of !id:

return [
  new Extend.Mentionables()
    .format(ExclamationFormat)
    .mentionable('!', DiscussionMention),
];

Screenshot
Screencast from 03-13-2023 10:45:59 AM.webm

Necessity

• Has the problem that is being solved here been clearly explained?
• If applicable, have various options for solving this problem been considered?
• For core PRs, does this need to be in core, or could it be in an extension?
• Are we willing to maintain this for years / potentially forever?

Confirmed

• Frontend changes: tested on a local Flarum installation.
• Backend changes: tests are green (run composer test).
• Core developer confirmed locally this works as intended.
• Tests have been added, or are not appropriate here.

Required changes:

• Related documentation PR: (Remove if irrelevant)
• Related core extension PRs: (Remove if irrelevant)

[luceos]

This works as intended, but is there a way to use routing instead of a href link?

[davwheat]

Without that, the linking wouldn't be accessible to screenreaders, nor indexable by search engines, though?

[SychO9]

Without that, the linking wouldn't be accessible to screenreaders, nor indexable by search engines, though?

It shouldn't be the case, the code already uses a click event use the mithril routing for user and post mentions.

[luceos]

I'd be okay for this to be merged for v1.8, we can properly test this in QA. In fact we should update our PR template to include a checklist item for "Provide steps to properly test this functionality still works during QA" (on it)