GitLab is used only for code review, issue tracking and project management. Canonical locations for source code are still https://gitweb.torproject.org/ https://git.torproject.org/ and git-rw.torproject.org.
Note that this pull request also includes my fix for #27315. This is because I use some of the refactoring I did for this fix. As such, this fix should be applied after #27315.
Github PR: https://github.com/torproject/tor/pull/2013