branch: error copying or renaming a detached HEAD

In c847f53712 (Detached HEAD (experimental), 2007-01-01) an error
condition was introduced in rename_branch() to prevent renaming, later
also copying, a detached HEAD.

The condition used was checking for NULL in oldname, the source branch
to rename/copy.  That condition cannot be satisfied because if no source
branch is specified, HEAD is going to be used in the call.

The error issued instead is:

	fatal: Invalid branch name: 'HEAD'

Let's remove the condition in copy_or_rename_branch() (the current
function name) and check for HEAD before calling it, dying with the
original intended error if we're in a detached HEAD.

Signed-off-by: Rubén Justo <rjusto@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 11 insertions, 0 deletions

diff --git a/t/t3200-branch.sh b/t/t3200-branch.sh
index 7d8edff9c3..38c57de71b 100755
--- a/t/t3200-branch.sh
+++ b/t/t3200-branch.sh
@@ -268,6 +268,17 @@ test_expect_success 'git branch -M topic topic should work when main is checked
 	git branch -M topic topic
 '
 
+test_expect_success 'git branch -M and -C fail on detached HEAD' '
+	git checkout HEAD^{} &&
+	test_when_finished git checkout - &&
+	echo "fatal: cannot rename the current branch while not on any." >expect &&
+	test_must_fail git branch -M must-fail 2>err &&
+	test_cmp expect err &&
+	echo "fatal: cannot copy the current branch while not on any." >expect &&
+	test_must_fail git branch -C must-fail 2>err &&
+	test_cmp expect err
+'
+
 test_expect_success 'git branch -v -d t should work' '
 	git branch t &&
 	git rev-parse --verify refs/heads/t &&