Subject: Re: [PATCH 4/3] branch: fix "copy" to never touch HEAD

From: Brandon Williams <[email-masked]>
Date: Fri, 22 Sep 2017 09:33:48 -0700

On 09/22, Junio C Hamano wrote:
> When creating a new branch B by copying the branch A that happens to
> be the current branch, it also updates HEAD to point at the new
> branch.  It probably was made this way because "git branch -c A B"
> piggybacked its implementation on "git branch -m A B",
> 
> This does not match the usual expectation.  If I were sitting on a
> blue chair, and somebody comes and repaints it to red, I would
> accept ending up sitting on a chair that is now red (I am also OK to
> stand, instead, as there no longer is my favourite blue chair).  But
> if somebody creates a new red chair, modelling it after the blue
> chair I am sitting on, I do not expect to be booted off of the blue
> chair and ending up on sitting on the new red one.
> 
> Let's fix this before it hits 'next'.  Those who want to create a
> new branch and switch to it can do "git checkout B" after doing a
> "git branch -c B", and if that operation is so useful and deserves a
> short-hand way to do so, perhaps extend "git checkout -b B" to copy
> configurations while creating the new branch B.
> 
> Signed-off-by: Junio C Hamano <[email-masked]>
> ---
> 
>  * Let's send an updated one as a follow-up to the discussion thread
>    that it is a follow-up to.  The patch in this message is the same
>    as the one I previously sent; the proposed log message has been
>    updated somewhat.
> 
>  builtin/branch.c  |  9 +++------
>  t/t3200-branch.sh | 10 +++++-----
>  2 files changed, 8 insertions(+), 11 deletions(-)
> 
> diff --git a/builtin/branch.c b/builtin/branch.c
> index 89f64f4123..e2e3692838 100644
> --- a/builtin/branch.c
> +++ b/builtin/branch.c
> @@ -506,12 +506,9 @@ static void copy_or_rename_branch(const char *oldname, const char *newname, int
>  				oldref.buf + 11);
>  	}
>  
> -	if (replace_each_worktree_head_symref(oldref.buf, newref.buf, logmsg.buf)) {
> -		if (copy)
> -			die(_("Branch copied to %s, but HEAD is not updated!"), newname);
> -		else
> -			die(_("Branch renamed to %s, but HEAD is not updated!"), newname);
> -	}
> +	if (!copy &&
> +	    replace_each_worktree_head_symref(oldref.buf, newref.buf, logmsg.buf))
> +		die(_("Branch renamed to %s, but HEAD is not updated!"), newname);
>  
>  	strbuf_release(&logmsg);
>  
> diff --git a/t/t3200-branch.sh b/t/t3200-branch.sh
> index 5d03ad16f6..be9b3784c6 100755
> --- a/t/t3200-branch.sh
> +++ b/t/t3200-branch.sh
> @@ -422,7 +422,7 @@ test_expect_success 'git branch --copy is a synonym for -c' '
>  	test_cmp expect actual
>  '
>  
> -test_expect_success 'git branch -c ee ef should copy and checkout branch ef' '
> +test_expect_success 'git branch -c ee ef should copy to create branch ef' '

The new wording seems to be missing something.  Maybe it should read:
  
  'git branch -c ee ef should copy branch ee to create branch ef'

>  	git checkout -b ee &&
>  	git reflog exists refs/heads/ee &&
>  	git config branch.ee.dummy Hello &&
> @@ -431,7 +431,7 @@ test_expect_success 'git branch -c ee ef should copy and checkout branch ef' '
>  	git reflog exists refs/heads/ef &&
>  	test $(git config branch.ee.dummy) = Hello &&
>  	test $(git config branch.ef.dummy) = Hello &&
> -	test $(git rev-parse --abbrev-ref HEAD) = ef
> +	test $(git rev-parse --abbrev-ref HEAD) = ee
>  '
>  
>  test_expect_success 'git branch -c f/f g/g should work' '
> @@ -494,12 +494,12 @@ test_expect_success 'git branch -C c1 c2 should succeed when c1 is checked out'
>  	git checkout -b c1 &&
>  	git branch c2 &&
>  	git branch -C c1 c2 &&
> -	test $(git rev-parse --abbrev-ref HEAD) = c2
> +	test $(git rev-parse --abbrev-ref HEAD) = c1
>  '
>  
> -test_expect_success 'git branch -C c1 c2 should add entries to .git/logs/HEAD' '
> +test_expect_success 'git branch -C c1 c2 should never touch HEAD' '
>  	msg="Branch: copied refs/heads/c1 to refs/heads/c2" &&
> -	grep "$msg$" .git/logs/HEAD
> +	! grep "$msg$" .git/logs/HEAD
>  '
>  
>  test_expect_success 'git branch -C master should work when master is checked out' '
> -- 
> 2.14.1-929-g25eae544e9
> 

The rest of the patch lgtm.  I agree that this is probably a better UI
than without this patch.  Especially since the vanilla behavior of git
branch is to create a new branch without moving you to that new branch.

-- 
Brandon Williams