Re: [PATCH] Proof-of-concept patch to remember what the detached HEAD was

Daniel Barkalow [off-list ref] writes:

 $ git checkout origin/master
 $ git fetch
 $ git checkout origin/next
 Uncommited file '...' would be overwritten.

If HEAD is a symref to refs/remotes/origin/master, and you update 
refs/remotes/origin/master, git will subsequently see that your index 
doesn't match HEAD, and when you switch branches, it will try to apply a 
revert to the branch you're switching to. It's the same issue as pushing 
into a non-bare repository.

I think the idea here is to allow HEAD to point at outside refs/heads/,
e.g. refs/remotes/origin/master, but forbid commit and other commands from
updating HEAD and its underlying ref via update_ref() unless HEAD is
detached or points at a local branch.