E0275: Point a additional error case while waiting for a proper fix

[louwenus]

Dirty fix to #145069
While waiting for a proper fix, at least document what is happening in the error so that the next to stumble on the issue hopefully does not waste too much time debugging it.

[rustbot]

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[rustbot]

⚠️ Warning ⚠️

• There are issue links (such as #123) in the commit messages of the following commits.
  Please move them to the PR description, to avoid spamming the issues with references to the commit, and so this bot can automatically canonicalize them to avoid issues with subtree.
  • 9c55d56

[louwenus]

⚠️ Warning ⚠️

* There are issue links (such as `#123`) in the commit messages of the following commits.
  _Please move them to the PR description, to avoid spamming the issues with references to the commit, and so this bot can automatically canonicalize them to avoid issues with subtree._
  
  * [9c55d56](https://github.com/rust-lang/rust/commit/9c55d5676bcb74b23934b7b4f3147cab4083a889)

Well it is in the PR description too, and I do not know how to edit commit message.
If it is important, could someone tell me how to do it ? Thanks

[madsmtm]

Hmm, I'm kinda of two minds about this. On one hand, I'm in favour of more docs, but on the other hand, generic_const_exprs is marked incomplete, so I don't really want to start calling out in docs everywhere that it doesn't work (especially because such documentation will easily get outdated).

Arguably, the problem is perhaps more that you're able to have a dependency that uses an incomplete feature like generic_const_exprs, and not get a warning about it when compiling the root crate?

I do not know how to edit commit message

There's many ways to do it, one option is to use git rebase, another is something like git commit --amend, I can recommend Chapter 7.6 in the Git Book. After that, you'll need to use a force push, something like git push --force-with-lease.

Feel free to ask questions about it, but perhaps let's discuss if this is something that we want to do first ;)