Fixes a bug [1] reported by Michael McClimon where rebase with oids will erroneously update the branch HEAD points to. 1. https://lore.kernel.org/git/xmqqsfrpbepd.fsf@gitster.g/ This patch has two parts: * updates rebase setup test to add some tags we will use, while swapping out manual commit creation with the test_commit helper * sets RESET_HARD_DETACH flag if branch is not a valid refname changes since v4: * got rid of test assertion that shows bug behavior * clarified commit message changes since v3: * fixed typos in commit message * added a test assertion to show bug behavior * included more replacements with test_commit changes since v2: * remove BUG assertion changes since v1: * only set RESET_HEAD_DETACH if is not a valid branch * updated tests to use existing setup John Cai (2): rebase: use test_commit helper in setup rebase: set REF_HEAD_DETACH in checkout_up_to_date() builtin/rebase.c | 2 ++ t/t3400-rebase.sh | 18 +++++++++++------- 2 files changed, 13 insertions(+), 7 deletions(-) base-commit: b896f729e240d250cf56899e6a0073f6aa469f5d Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-1226%2Fjohn-cai%2Fjc%2Ffix-rebase-oids-v5 Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-1226/john-cai/jc/fix-rebase-oids-v5 Pull-Request: https://github.com/git/git/pull/1226 Range-diff vs v4: 1: cac51a949ee < -: ----------- rebase: test showing bug in rebase with non-branch 2: 5c40e116eba ! 1: 9dbd2ba430a rebase: use test_commit helper in setup @@ t/t3400-rebase.sh: test_expect_success 'prepare repository with topic branches' git checkout -f main && echo Third >>A && git update-index A && - git commit -m "Modify A." && - git checkout -b side my-topic-branch && -- echo Side >>C && -- git add C && -- git commit -m "Add C" && -+ test_commit --no-tag "Add C" C Side && - git checkout -f my-topic-branch && - git tag topic - ' -@@ t/t3400-rebase.sh: test_expect_success 'rebase off of the previous branch using "-"' ' - test_expect_success 'rebase a single mode change' ' - git checkout main && - git branch -D topic && -- echo 1 >X && -- git add X && -- test_tick && -- git commit -m prepare && -+ test_commit prepare X 1 && - git checkout -b modechange HEAD^ && - echo 1 >X && - git add X && 3: 13c5955c317 ! 2: 1dd5bb21012 rebase: set REF_HEAD_DETACH in checkout_up_to_date() @@ Metadata ## Commit message ## rebase: set REF_HEAD_DETACH in checkout_up_to_date() - Fixes a bug whereby rebase updates the deferenced reference HEAD points - to instead of HEAD directly. - - If HEAD is on main and if the following is a fast-forward operation, - - git rebase $(git rev-parse main) $(git rev-parse topic) - - Instead of HEAD being set to $(git rev-parse topic), rebase erroneously - dereferences HEAD and sets main to $(git rev-parse topic). See [1] for - the original bug report. + "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() + cmd_rebase() + -> checkout_up_to_date() + -> reset_head() + -> update_refs() + -> update_ref() - When <branch> 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(). + 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, which in the above example is main. - - The correct behavior is that git rebase should update HEAD to $(git - rev-parse topic) without dereferencing it. + pointing to. We want the HEAD detached at B instead. - Fix this bug by adding the RESET_HEAD_DETACH flag in checkout_up_to_date - if <branch> is not a valid branch. so that once reset_head() calls - update_refs(), it calls update_ref() with REF_NO_DEREF which updates - HEAD directly intead of deferencing it and updating the branch that HEAD - points to. + Fix this bug by adding the RESET_HEAD_DETACH flag in + checkout_up_to_date if B is not a valid branch, so that once + reset_head() calls update_refs(), it calls update_ref() with + REF_NO_DEREF which updates HEAD directly intead of deferencing it + and updating the branch that HEAD points to. Also add a test to ensure the correct behavior. - 1. https://lore.kernel.org/git/xmqqsfrpbepd.fsf@gitster.g/ + [1] https://lore.kernel.org/git/YiokTm3GxIZQQUow@newk/ + Reported-by: Michael McClimon <michael@xxxxxxxxxxxx> Signed-off-by: John Cai <johncai86@xxxxxxxxx> + Signed-off-by: Junio C Hamano <gitster@xxxxxxxxx> ## builtin/rebase.c ## @@ builtin/rebase.c: static int checkout_up_to_date(struct rebase_options *options) @@ t/t3400-rebase.sh: test_expect_success 'switch to branch not checked out' ' git rebase main other ' --test_expect_success 'switch to non-branch changes branch HEAD points to' ' +test_expect_success 'switch to non-branch detaches HEAD' ' - git checkout main && - old_main=$(git rev-parse HEAD) && - git rebase First Second^0 && -- test_cmp_rev HEAD main && -- test_cmp_rev main $(git rev-parse Second) && -- git symbolic-ref HEAD ++ git checkout main && ++ old_main=$(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 && -- gitgitgadget
