Add star in archived repo results in an error

[Aragur]

• Can you reproduce the bug at https://try.gitea.io:
  • Yes https://try.gitea.io/AragurDEV/Archived_Repo

Description

See my repo on try.gitea.io.
Try to star it. This results in the following error

template: repo/header:31:51: executing "repo/header" at <$.UnitTypeCode>: invalid value; expected models.UnitType

[jolheiser]

This same thing happens when you click on watch in that repo, which narrows it down to most likely being the code here:
https://github.com/go-gitea/gitea/blob/master/routers/repo/repo.go#L288-L316

Nevermind, I think this is actually a context issue.

[jolheiser]

The issue presented is partially caused by #5980
Now that the 404 page is loading a repo header if possible, this was failing because unit types aren't loaded for the action URL and the archived status is returning a 404 on actions.
I will send a PR to fix this, however I think there may be more work to be done after that.

---

In my opinion, it may be confusing to the end user why they get a 404 that displays the repo header, however they were unable to (un)watch/star the repo.

We could disable the buttons similarly to how the fork button is disabled if the user cannot fork, but...

1. Shouldn't a user be able to, at the very least, unstar/watch an archived repo?
2. Should all watchers and/or stargazers be removed when a repo is archived automatically? (I understand having a starred archived repo since you can still clone/download, but watching would be pretty moot)

In addition, should we display an error to the end user explaining that archived repos cannot be (un)watched/starred?

[Aragur]

I think it should be possible to (un)star a archived repo. As of watching it's not that useful but I think enabling it would be better considering usibility

[jolheiser]

For comparison, GitHub allows you to still fully interact with starring/watching an archived repo.