From bdff97a3f6e66107abd136815c8fa1eda5c67aca Mon Sep 17 00:00:00 2001 From: John Cai Date: Fri, 18 Mar 2022 13:54:03 +0000 Subject: rebase: set REF_HEAD_DETACH in checkout_up_to_date() "git rebase A B" where B is not a commit should behave as if the HEAD got detached at B and then the detached HEAD got rebased on top of A. A bug however overwrites the current branch to point at B, when B is a descendant of A (i.e. the rebase ends up being a fast-forward). See [1] for the original bug report. The callstack from checkout_up_to_date() is the following: cmd_rebase() -> checkout_up_to_date() -> reset_head() -> update_refs() -> update_ref() When B is not a valid branch but an oid, rebase sets the head_name of rebase_options to NULL. This value gets passed down this call chain through the branch member of reset_head_opts also getting set to NULL all the way to update_refs(). Then update_refs() checks ropts.branch to decide whether or not to switch branches. If ropts.branch is NULL, it calls update_ref() to update HEAD. At this point however, from rebase's point of view, we want a detached HEAD. But, since checkout_up_to_date() does not set the RESET_HEAD_DETACH flag, the update_ref() call will deference HEAD and update the branch its pointing to. We want the HEAD detached at B instead. Fix this bug by adding the RESET_HEAD_DETACH flag in checkout_up_to_date if B is not a valid branch, so that once reset_head() calls update_refs(), it calls update_ref() with REF_NO_DEREF which updates HEAD directly intead of deferencing it and updating the branch that HEAD points to. Also add a test to ensure the correct behavior. [1] https://lore.kernel.org/git/YiokTm3GxIZQQUow@newk/ Reported-by: Michael McClimon Signed-off-by: John Cai Signed-off-by: Junio C Hamano --- t/t3400-rebase.sh | 9 +++++++++ 1 file changed, 9 insertions(+) (limited to 't') diff --git a/t/t3400-rebase.sh b/t/t3400-rebase.sh index 0643d01525..d5a8ee39fc 100755 --- a/t/t3400-rebase.sh +++ b/t/t3400-rebase.sh @@ -394,6 +394,15 @@ test_expect_success 'switch to branch not checked out' ' git rebase main other ' +test_expect_success 'switch to non-branch detaches HEAD' ' + git checkout main && + old_main=$(git rev-parse HEAD) && + git rebase First Second^0 && + test_cmp_rev HEAD Second && + test_cmp_rev main $old_main && + test_must_fail git symbolic-ref HEAD +' + test_expect_success 'refuse to switch to branch checked out elsewhere' ' git checkout main && git worktree add wt && -- cgit v1.2.3