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> 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!
> Rubén Justo <rjusto@gmail.com>