Viewing a file in the "HEAD" branch yields a 404 "history" link (404 links produced when viewing symbolic ref)
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### Summary
Open these two links:
* https://gitlab.com/gitlab-org/gitlab-ce/blob/master/README.md
* https://gitlab.com/gitlab-org/gitlab-ce/blob/HEAD/README.md
Clicking "history" produces a 404 for `HEAD` but not for `master`. I.e. this link (https://gitlab.com/gitlab-org/gitlab-ce/commits/master/README.md) works, but this one fails: https://gitlab.com/gitlab-org/gitlab-ce/commits/HEAD/README.md
### Steps to reproduce
See above. This is on gitlab.com running 11.7.4-ee, we run 11.6.5-ee and see the same issue. I'm pretty sure (but have not confirmed) that this used to work in some recent-ish version, and that this is a regression.
### Why is this needed?
It's handy to be able to link to the `HEAD` branch from tools that given some filename in the project just want to be able to browse it at the latest version, whether the `HEAD` symbolic ref points to `master`, `trunk` or something else.
issue