[PATCH v4 1/3] rebase: test showing bug in rebase with non-branch

["John Cai via GitGitGadget" <gitgitgadget@gmail.com>]

From: John Cai <johncai86@gmail.com>

Currently when rebase is used with a non branch, and <oid> is up to
date with base:

git rebase base <oid>

It will update the ref that HEAD is pointing at to <oid>, and leave HEAD
unmodified.

This is a bug. The expected behavior is that the branch HEAD points at
remains unmodified while HEAD is updated to point to <oid> in detached
HEAD mode.

Signed-off-by: John Cai <johncai86@gmail.com>
Reported-by: Michael McClimon <michael@mcclimon.org>
---
 t/t3400-rebase.sh | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/t/t3400-rebase.sh b/t/t3400-rebase.sh
index 71b1735e1dd..5c4073f06d6 100755
--- a/t/t3400-rebase.sh
+++ b/t/t3400-rebase.sh
@@ -399,6 +399,15 @@ test_expect_success 'switch to branch not checked out' '
 	git rebase main other
 '
 
+test_expect_success 'switch to non-branch changes branch HEAD points to' '
+	git checkout main &&
+	old_main=$(git rev-parse HEAD) &&
+	git rebase First Second^0 &&
+	test_cmp_rev HEAD main &&
+	test_cmp_rev main $(git rev-parse Second) &&
+	git symbolic-ref HEAD
+'
+
 test_expect_success 'refuse to switch to branch checked out elsewhere' '
 	git checkout main &&
 	git worktree add wt &&
-- 
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