[PATCH v2 2/4] branch -m: allow renaming a yet-unborn branch

["Johannes Schindelin via GitGitGadget" <gitgitgadget@gmail.com>]

From: Johannes Schindelin <johannes.schindelin@gmx.de>

In one of the next commits, we would like to give users some advice
regarding the initial branch name, and how to modify it.

To that end, it would be good if `git branch -m <name>` worked in a
freshly initialized repository without any commits. Let's make it so.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---
 builtin/branch.c | 3 ++-
 t/t0001-init.sh  | 6 ++++++
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/builtin/branch.c b/builtin/branch.c
index efb30b8820..10609981e6 100644
--- a/builtin/branch.c
+++ b/builtin/branch.c
@@ -538,7 +538,8 @@ static void copy_or_rename_branch(const char *oldname, const char *newname, int
 		strbuf_addf(&logmsg, "Branch: renamed %s to %s",
 			    oldref.buf, newref.buf);
 
-	if (!copy && rename_ref(oldref.buf, newref.buf, logmsg.buf))
+	if (!copy && (oldname != head || !is_null_oid(&head_oid)) &&
+	    rename_ref(oldref.buf, newref.buf, logmsg.buf))
 		die(_("Branch rename failed"));
 	if (copy && copy_existing_ref(oldref.buf, newref.buf, logmsg.buf))
 		die(_("Branch copy failed"));
diff --git a/t/t0001-init.sh b/t/t0001-init.sh
index 69a320489f..69c5ad179c 100755
--- a/t/t0001-init.sh
+++ b/t/t0001-init.sh
@@ -571,4 +571,10 @@ test_expect_success 'invalid default branch name' '
 	test_i18ngrep "invalid branch name" err
 '
 
+test_expect_success 'branch -m with the initial branch' '
+	git init rename-initial-branch &&
+	git -C rename-initial-branch branch -m renamed &&
+	test renamed = $(git -C rename-initial-branch symbolic-ref --short HEAD)
+'
+
 test_done
-- 
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