Re: [PATCH 7/7] push: clarify rejection of update to non-commit-ish

>> With this code, the old must be a commit but new can be a tag that
>> points at a commit?  Why?
>
> The old must not be a tag because fast-forwarding from it is
> potentially destructive; a tag would likely be left dangling in this
> case.  This is not true for the new, though.   I'm not sure
> fast-forwarding from a commit to a tag is useful, but I didn't see a
> reason to prevent it either.   The refs/tags/ hierarchy is excluded
> from fast-forwarding before this check, and refs/heads/ is already
> protected against anything but commits.  So it seems very unlikely
> that someone would accidentally make use of this behavior.
>
> So, fast-forwarding to a tag seemed fairly benign and unlikely to
> cause confusion, so I leaned towards allowing it in case someone found
> a use case for it.