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From: Victoria Dye <vdye@github.com>
To: "Rubén Justo" <rjusto@gmail.com>, "Git List" <git@vger.kernel.org>
Cc: "Ævar Arnfjörð Bjarmason" <avarab@gmail.com>,
	"Taylor Blau" <me@ttaylorr.com>
Subject: Re: [PATCH 1/2] branch: force-copy a branch to itself via @{-1} is a no-op
Date: Thu, 17 Nov 2022 14:18:09 -0800	[thread overview]
Message-ID: <9125ea40-3078-2ca3-493c-56703144f37e@github.com> (raw)
In-Reply-To: <db182322-1383-4311-8baa-c4a9aeed3b4d@gmail.com>

Rubén Justo wrote:
> Since 52d59cc645 (branch: add a --copy (-c) option to go with --move
> (-m), 2017-06-18) we can copy a branch to make a new branch with the
> '-c' (copy) option or to overwrite an existing branch using the '-C'
> (force copy) option.  A no-op possibility is considered when we are
> asked to copy a branch to itself, to follow the same no-op introduced
> for the rename (-M) operation in 3f59481e33 (branch: allow a no-op
> "branch -M <current-branch> HEAD", 2011-11-25).  To check for this, in
> 52d59cc645 we compared the branch names provided by the user, source
> (HEAD if omitted) and destination, and a match is considered as this
> no-op.
> 
> Since ae5a6c3684 (checkout: implement "@{-N}" shortcut name for N-th
> last branch, 2009-01-17) a branch can be specified using shortcuts like
> @{-1}.  This allows this usage:
> 
> 	$ git checkout -b test
> 	$ git checkout -
> 	$ git branch -C test test  # no-op
> 	$ git branch -C test @{-1} # oops
> 	$ git branch -C @{-1} test # oops
> 
> As we are using the branch name provided by the user to do the
> comparison, if one of the branches is provided using a shortcut we are
> not going to have a match and a call to git_config_copy_section() will
> happen.  This will make a duplicate of the configuration for that
> branch, and with this progression the second call will produce four
> copies of the configuration, and so on.

This is a clear explanation of what the issue is and why it's happening.

> 
> Let's use the interpreted branch name instead for this comparison.
> 
> The rename operation is not affected.
> 
> Signed-off-by: Rubén Justo <rjusto@gmail.com>
> ---
>  builtin/branch.c                      |  6 +++---
>  t/t3204-branch-name-interpretation.sh | 10 ++++++++++
>  2 files changed, 13 insertions(+), 3 deletions(-)
> 
> diff --git a/builtin/branch.c b/builtin/branch.c
> index 15be0c03ef..a35e174aae 100644
> --- a/builtin/branch.c
> +++ b/builtin/branch.c
> @@ -584,13 +584,13 @@ static void copy_or_rename_branch(const char *oldname, const char *newname, int
>  	strbuf_release(&logmsg);
>  
>  	strbuf_addf(&oldsection, "branch.%s", interpreted_oldname);
> -	strbuf_release(&oldref);
>  	strbuf_addf(&newsection, "branch.%s", interpreted_newname);
> -	strbuf_release(&newref);
>  	if (!copy && git_config_rename_section(oldsection.buf, newsection.buf) < 0)
>  		die(_("Branch is renamed, but update of config-file failed"));
> -	if (copy && strcmp(oldname, newname) && git_config_copy_section(oldsection.buf, newsection.buf) < 0)
> +	if (copy && strcmp(interpreted_oldname, interpreted_newname) && git_config_copy_section(oldsection.buf, newsection.buf) < 0)

I double-checked that 'interpreted_oldname' and 'interpreted_newname' are
always set (and not only when a shortcut name is used), and they are. So,
this does exactly what you intend.

>  		die(_("Branch is copied, but update of config-file failed"));
> +	strbuf_release(&oldref);
> +	strbuf_release(&newref);
>  	strbuf_release(&oldsection);
>  	strbuf_release(&newsection);
>  }
> diff --git a/t/t3204-branch-name-interpretation.sh b/t/t3204-branch-name-interpretation.sh
> index 793bf4d269..3399344f25 100755
> --- a/t/t3204-branch-name-interpretation.sh
> +++ b/t/t3204-branch-name-interpretation.sh
> @@ -57,6 +57,16 @@ test_expect_success 'create branch with pseudo-qualified name' '
>  	expect_branch refs/heads/refs/heads/qualified two
>  '
>  
> +test_expect_success 'force-copy a branch to itself via @{-1} is no-op' '
> +	git branch -t copiable main &&
> +	git checkout copiable &&
> +	git checkout - &&
> +	git branch -C @{-1} copiable &&
> +	git config --get-all branch.copiable.merge >actual &&
> +	echo refs/heads/main >expect &&
> +	test_cmp expect actual
> +'
> +

And the test is straightforward and demonstrates the fix. Thanks for the
well-written patch, this looks good to me! 


  reply	other threads:[~2022-11-17 22:19 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-11-17  1:33 [PATCH 0/2] branch: fix some malfunctions in -m/-c Rubén Justo
2022-11-17  1:36 ` [PATCH 1/2] branch: force-copy a branch to itself via @{-1} is a no-op Rubén Justo
2022-11-17 22:18   ` Victoria Dye [this message]
2022-11-20  8:10     ` Rubén Justo
2022-11-18  3:58   ` Ævar Arnfjörð Bjarmason
2022-11-20  9:34     ` Rubén Justo
2022-11-17  1:44 ` [PATCH 2/2] branch: clear target branch configuration before copying or renaming Rubén Justo
2022-11-18  2:10   ` Victoria Dye
2022-11-20  9:20     ` Rubén Justo
2022-11-20 22:10       ` Victoria Dye
2022-11-21 23:13         ` Rubén Justo
2022-11-18  4:51   ` Ævar Arnfjörð Bjarmason
2022-11-18 16:36     ` Victoria Dye
2022-11-18 18:12       ` Ævar Arnfjörð Bjarmason
2022-11-20 14:55         ` Rubén Justo

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