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

On Tue, Jun 13 2017, Jonathan Nieder jotted:

Hi,

Ævar Arnfjörð Bjarmason wrote:

quoted

So the reason we have this for -m is:

    commit 3f59481e33
    Author: Jonathan Nieder [off-list ref]
    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.

I may be missing some context, but notice that the above mentioned
commit is about -M, not -m.

The context was just that that commit added a change in how -M
interacted when clobbering the current HEAD, and that -C should have a
test for that behavior, which the patch now submitted to the list has:

    +test_expect_success 'git branch -C master master should work when master is checked out' '
    +       git checkout master &&
    +       git branch -C master master
    +'