[mentions] feat: group mentions

[imorland]

**Addresses https://discuss.flarum.org/d/31473-mentioning-groups-within-posts **

Changes proposed in this pull request:
Allows mentioning of groups

Reviewers should focus on:

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[2022-10-21 17:54:02] flarum.INFO: Message-ID: <[email protected]>
Date: Fri, 21 Oct 2022 17:54:02 +0000
Subject: admin mentioned a group you're a member of in Example discussion
From: Flarum Dev Docker <noreply@localhost>
To: admin <[email protected]>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: quoted-printable

Hey admin!

admin mentioned a group you're a member of in Example discussion.

http://dev.lan/d/1/33

---

@"Admins"#g1 

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)

[SychO9]

Looks neat! a few comments:

• Groups are loaded from the store for autocomplete, do we know if all groups are within the store at that point? part of the requirements suggests an API search endpoint.
• I have yet to test locally, but I think we might be missing taking into consideration hidden groups.
• To avoid abuse, I reckon we need a mention groups permission,but since it wasn't listed in the initial requirements, we can add it inanother PR outside of this.

[imorland]

• Groups are loaded from the store for autocomplete, do we know if all groups are within the store at that point? part of the requirements suggests an API search endpoint.

🤦‍♂️ whoops, yes I missed that. I feel the search endpoint should probably be in core, rather than mentions, what is your opinion?

• I have yet to test locally, but I think we might be missing taking into consideration hidden groups.

As it stands, yes, hidden groups are not returned for users who do not have permission to view them.

• To avoid abuse, I reckon we need a mention groups permission,but since it wasn't listed in the initial requirements, we can add it inanother PR outside of this.

I'm happy to include that in this PR, as it makes complete sense to do that at the same time. Again, probably for core directly, rather than in mentions?

[SychO9]

I feel the search endpoint should probably be in core, rather than mentions, what is your opinion?

Yup. core makes sense.

I'm happy to include that in this PR, as it makes complete sense to do that at the same time. Again, probably for core directly, rather than in mentions?

mention groups permission is only relevant in the mentions extension, so it makes more sense in mentions than in core imo.

[imorland]

Note: PHPStan failure is fixed by #3665 by @SychO9

[SychO9]

Added a few more tests, one of them actually caught a bug where the editing of posts doesn't have the actor so group mentions don't work. pushed a fix at the same time.

I believe this is ready now.

[imorland]

Added a few more tests, one of them actually caught a bug where the editing of posts doesn't have the actor so group mentions don't work. pushed a fix at the same time.

Ah nice one, thank you!