Re: [PATCH/RFC] branch: add tests for new copy branch feature

> So the reason we have this for -m is:
>
>     commit 3f59481e33
>     Author: Jonathan Nieder <jrnieder@gmail.com>
>     Date:   Fri Nov 25 20:30:02 2011 -0600
>
>     branch: allow a no-op "branch -M <current-branch> HEAD"
>
>     Overwriting the current branch with a different commit is forbidden, as it
>     will make the status recorded in the index and the working tree out of
>     sync with respect to the HEAD. There however is no reason to forbid it if
>     the current branch is renamed to itself, which admittedly is something
>     only an insane user would do, but is handy for scripts.
>
> My understanding of that last part is that Jonathan/someone (see
> reported-by in that patch) had some script which was renaming
> branches, and it was easier for whatever reason to just make it no-op
> if the rename would have yielded the same result as doing nothing at
> all.
>
> Most likely your implementation will consist of just re-using the
> logic in rename_branch() (and renaming it to e.g.
> copy_or_rename_branch() ...) so you could just re-use the no-op
> behavior we use for -m, or if there's some reason not to no-op and
> error instead for -c we could just do that, but in any case this case
> of `git branch -c master master` or `git branch -c currentbranch`
> should be tested for.