Request for comments on dry-run Trac -> GitLab migration

[Niklas Hambüchen]

I find that commits aren't mentioned on the corresponding issues, for example there's no equivalent of

     https://ghc.haskell.org/trac/ghc/ticket/13497#comment:27

on

     https://gitlab.staging.haskell.org/ghc/ghc/issues/13497

I vaguely remember these "commit posts" being discussed before somewhere.
But that's not even what I'm after.

The commit itself mentions the ticket ("This fixes #13497").
Usually when such a commit is pushed to Gitlab, it automatically creates an entry like:

      Niklas Hambüchen @nh2 mentioned in commit abc123456 3 months ago

But this isn't the case here.
Is it because the issues were imported *after* the repo commits already exist?

Can it be fixed?
E.g. can Gitlab be told to re-index the repo accordingly?
Or could it be done by deleting `master` and re-pushing the entire history?