"John Cai via GitGitGadget" <gitgitgadget@xxxxxxxxx> writes: > From: John Cai <johncai86@xxxxxxxxx> > > Fixes a bug whereby rebase updates the deferenced reference HEAD points > to instead of HEAD directly. Perhaps "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. OK (URL is wrong; see below). The explanation of how the bug occurs (elided) in the patch looked all reasonable. It read well. > ... > Also add a test to ensure the correct behavior. Yup. _Add_ a test to ensure that. Not replace a misleading test that expected to see a wrong behaviour. > 1. https://lore.kernel.org/git/xmqqsfrpbepd.fsf@gitster.g/ This is not the original bug report. It was an early hint for diagnosis. [1] https://lore.kernel.org/git/YiokTm3GxIZQQUow@newk/ would be a more appropriate pointer. > ropts.oid = &options->orig_head; > ropts.branch = options->head_name; > ropts.flags = RESET_HEAD_RUN_POST_CHECKOUT_HOOK; > + if (!ropts.branch) > + ropts.flags |= RESET_HEAD_DETACH; > ropts.head_msg = buf.buf; OK. If head_name is not set, we do not want to touch the branch the HEAD happens to be pointing at, so we want to detach. > +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 main && > - test_cmp_rev main $(git rev-parse Second) && > - git symbolic-ref HEAD > + test_cmp_rev HEAD Second && > + test_cmp_rev main $old_main && > + test_must_fail git symbolic-ref HEAD As we want (1) HEAD (detached) is pointing at Second, (2) 'main' stayed at $old_main, and (3) HEAD is detched, these three conditions look sane. Thanks. For reference, I discarded [1/3], queued [2/3] and replaced this [3/3] with the following for now. ---- >8 ---- ---- >8 ---- ---- >8 ---- ---- >8 ---- ---- >8 ---- From: John Cai <johncai86@xxxxxxxxx> Subject: [PATCH] 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 <michael@xxxxxxxxxxxx> Signed-off-by: John Cai <johncai86@xxxxxxxxx> Signed-off-by: Junio C Hamano <gitster@xxxxxxxxx> --- builtin/rebase.c | 2 ++ t/t3400-rebase.sh | 9 +++++++++ 2 files changed, 11 insertions(+) diff --git a/builtin/rebase.c b/builtin/rebase.c index b29ad2b65e..27fde7bf28 100644 --- a/builtin/rebase.c +++ b/builtin/rebase.c @@ -829,6 +829,8 @@ static int checkout_up_to_date(struct rebase_options *options) ropts.oid = &options->orig_head; ropts.branch = options->head_name; ropts.flags = RESET_HEAD_RUN_POST_CHECKOUT_HOOK; + if (!ropts.branch) + ropts.flags |= RESET_HEAD_DETACH; ropts.head_msg = buf.buf; if (reset_head(the_repository, &ropts) < 0) ret = error(_("could not switch to %s"), options->switch_to); diff --git a/t/t3400-rebase.sh b/t/t3400-rebase.sh index 6dc8df8be7..cf55b017ff 100755 --- a/t/t3400-rebase.sh +++ b/t/t3400-rebase.sh @@ -389,6 +389,15 @@ 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 && -- 2.35.1-757-g4266a5c05c