git/list[1] front-page[2] threads[3] people[4] search[5] about
 

Re: [PATCH] rebase: set REF_HEAD_DETACH in checkout_up_to_date()

From
John Cai <johncai86@gmail.com>
Date
Mar 11, 2022, 15:28 UTC
Message-ID
<6BBE6E16-C4CE-4A66-8A0F-1FDBCA0080D4@gmail.com>
In-Reply-To
<7c1c0b8e-7895-7a0e-6ab0-e45e21ec7329@gmail.com>
Hi Phillip,
On 11 Mar 2022, at 10:05, Phillip Wood wrote:
Show 19 quoted lines
> Hi John
>
> Thanks for working on this
>
> On 11/03/2022 05:05, John Cai via GitGitGadget wrote:
>> From: John Cai <johncai86@gmail.com>
>>
>> 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). This bug was
>> reported by Michael McClimon. See [1].
>
> Often we just add a Reported-by: trailer unless the liked email has some useful extra info (which arguably should not be the case with a well written commit message)
Thanks, will adjust.
Show 61 quoted lines
>
>> This is happening because on a fast foward with an oid as a <branch>,
>> update_refs() will only call update_ref() with REF_NO_DEREF if
>> RESET_HEAD_DETACH is set. This change was made in 176f5d96 (built-in rebase
>> --autostash: leave the current branch alone if possible,
>> 2018-11-07). In rebase, we are not setting the RESET_HEAD_DETACH flag,
>> which means that the update_ref() call ends up dereferencing
>> HEAD and updating it to the oid used as <branch>.
>>
>> The correct behavior is that git rebase should update HEAD to $(git
>> rev-parse topic) without dereferencing it.
>>
>> Fix this bug by adding the RESET_HEAD_DETACH flag in checkout_up_to_date
>
> As Junio points out it is confusing that it is always ok to pass that flag, I think we should only set it if we are not checking out a branch, see below.
>
>> 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 this behavior.
>>
>> 1. https://lore.kernel.org/git/xmqqsfrpbepd.fsf@gitster.g/
>
> Maybe
> Reported-by: Michael McClimon <michael@mcclimon.org>
> ?
>
>> Signed-off-by: John Cai <johncai86@gmail.com>
>> ---
>>      rebase: update HEAD when is an oid
>>          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/
>>
>> Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-1226%2Fjohn-cai%2Fjc%2Ffix-rebase-oids-v1
>> Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-1226/john-cai/jc/fix-rebase-oids-v1
>> Pull-Request: https://github.com/git/git/pull/1226
>>
>>   builtin/rebase.c  |  2 +-
>>   t/t3400-rebase.sh | 21 +++++++++++++++++++++
>>   2 files changed, 22 insertions(+), 1 deletion(-)
>>
>> diff --git a/builtin/rebase.c b/builtin/rebase.c
>> index b29ad2b65e7..52afeffcc2e 100644
>> --- a/builtin/rebase.c
>> +++ b/builtin/rebase.c
>> @@ -828,7 +828,7 @@ static int checkout_up_to_date(struct rebase_options *options)
>>   		    options->switch_to);
>>   	ropts.oid = &options->orig_head;
>>   	ropts.branch = options->head_name;
>> -	ropts.flags = RESET_HEAD_RUN_POST_CHECKOUT_HOOK;
>> +	ropts.flags = RESET_HEAD_RUN_POST_CHECKOUT_HOOK | RESET_HEAD_DETACH;
>
> I think it would be clearer if the post image ended up as
>
> 	ropts.flags = RESET_HEAD_RUN_POST_CHECKOUT_HOOK
> 	if (options->head_name)
> 		ropts.branch = option->head_name
> 	else
> 		ropts.flags |= RESET_HEAD_DETACH
Yes, this is what I had in mind as well :).
>
> and we changed reset_head() to BUG() if both branch and RESET_HEAD_DETACH are given.
I didn't consider this though, thanks for the suggestion.
Show 33 quoted lines
>
>>   	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 71b1735e1dd..0b92e78976c 100755
>> --- a/t/t3400-rebase.sh
>> +++ b/t/t3400-rebase.sh
>> @@ -437,4 +437,25 @@ test_expect_success 'rebase when inside worktree subdirectory' '
>>   	)
>>   '
>>  +test_expect_success 'rebase with oids' '
>> +	git init main-wt &&
>> +	(
>> +		cd main-wt &&
>> +		>file &&
>> +		git add file &&
>> +		git commit -m initial &&
>> +		git checkout -b side &&
>> +		echo >>file &&
>> +		git commit -a -m side &&
>> +		git checkout main &&
>> +		git tag hold &&
>> +		git checkout -B main hold &&
>> +		git rev-parse main >pre &&
>> +		git rebase $(git rev-parse main) $(git rev-parse side) &&
>> +		git rev-parse main >post &&
>> +		test "$(git rev-parse side)" = "$(cat .git/HEAD)" &&
>> +		test_cmp pre post
>> +	)
>> +'
>
> Using a stand alone test for bisecting makes sense but I think we should try and use the existing test setup for the regression test (it certainly does not need to run in its own worktree). The diff below shows how this could be done. Ideally there would be a preparatory commit that modernized the whole of the setup test rather than just the two commits we're using in the new test but that's not essential.
sounds good to me, might as well clean things up while we're at it.
Show 49 quoted lines
>
> Best Wishes
>
> Phillip
>
> ---- >8 ----
> diff --git a/t/t3400-rebase.sh b/t/t3400-rebase.sh
> index 71b1735e1d..d5a8ee39fc 100755
> --- a/t/t3400-rebase.sh
> +++ b/t/t3400-rebase.sh
> @@ -18,10 +18,7 @@ GIT_AUTHOR_EMAIL=bogus@email@address
>  export GIT_AUTHOR_NAME GIT_AUTHOR_EMAIL
>
>  test_expect_success 'prepare repository with topic branches' '
> -       git config core.logAllRefUpdates true &&
> -       echo First >A &&
> -       git update-index --add A &&
> -       git commit -m "Add A." &&
> +       test_commit "Add A." A First First &&
>         git checkout -b force-3way &&
>         echo Dummy >Y &&
>         git update-index --add Y &&
> @@ -32,9 +29,7 @@ test_expect_success 'prepare repository with topic branches' '
>         git mv A D/A &&
>         git commit -m "Move A." &&
>         git checkout -b my-topic-branch main &&
> -       echo Second >B &&
> -       git update-index --add B &&
> -       git commit -m "Add B." &&
> +       test_commit "Add B." B Second Second &&
>         git checkout -f main &&
>         echo Third >>A &&
>         git update-index A &&
> @@ -399,6 +394,15 @@ test_expect_success 'switch to branch not checked out' '
>         git rebase main other
>  '
>
> +test_expect_success 'switch to non-branch detaches HEAD' '
> +       git checkout main &&
> +       old_main=$(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 &&
Previous: Phillip WoodNext: John Cai
Message 6 of 41 in “rebase: set REF_HEAD_DETACH in checkout_up_to_date()”
  1. rebase: set REF_HEAD_DETACH in checkout_up_to_date()John Cai via GitGitGadget, Mar 11, 2022
  2. Junio C HamanoMar 11, 2022
  3. Junio C HamanoMar 11, 2022
  4. John CaiMar 11, 2022
  5. Phillip WoodMar 11, 2022
  6. John CaiMar 11, 2022
  7. John CaiMar 11, 2022
  8. Phillip WoodMar 11, 2022
  9. 0/2 rebase: update HEAD when is an oidJohn Cai via GitGitGadget, Mar 11, 2022
  10. 1/2 rebase: use test_commit helper in setupJohn Cai via GitGitGadget, Mar 11, 2022
  11. Junio C HamanoMar 13, 2022
  12. Phillip WoodMar 14, 2022
  13. Junio C HamanoMar 14, 2022
  14. 2/2 rebase: set REF_HEAD_DETACH in checkout_up_to_date()John Cai via GitGitGadget, Mar 11, 2022
  15. Junio C HamanoMar 13, 2022
  16. Phillip WoodMar 14, 2022
  17. Phillip WoodMar 14, 2022
  18. John CaiMar 14, 2022
  19. Phillip WoodMar 14, 2022
  20. 0/2 rebase: update HEAD when is an oidJohn Cai via GitGitGadget, Mar 17, 2022
  21. 2/2 rebase: set REF_HEAD_DETACH in checkout_up_to_date()John Cai via GitGitGadget, Mar 17, 2022
  22. Ævar Arnfjörð BjarmasonMar 17, 2022
  23. Junio C HamanoMar 17, 2022
  24. 1/2 rebase: use test_commit helper in setupJohn Cai via GitGitGadget, Mar 17, 2022
  25. Ævar Arnfjörð BjarmasonMar 17, 2022
  26. 0/3 rebase: update HEAD when is an oidJohn Cai via GitGitGadget, Mar 17, 2022
  27. 1/3 rebase: test showing bug in rebase with non-branchJohn Cai via GitGitGadget, Mar 17, 2022
  28. Junio C HamanoMar 17, 2022
  29. Junio C HamanoMar 17, 2022
  30. John CaiMar 17, 2022
  31. 2/3 rebase: use test_commit helper in setupJohn Cai via GitGitGadget, Mar 17, 2022
  32. Phillip WoodMar 18, 2022
  33. John CaiMar 18, 2022
  34. 3/3 rebase: set REF_HEAD_DETACH in checkout_up_to_date()John Cai via GitGitGadget, Mar 17, 2022
  35. Junio C HamanoMar 17, 2022
  36. John CaiMar 18, 2022
  37. 0/2 rebase: update HEAD when is an oidJohn Cai via GitGitGadget, Mar 18, 2022
  38. 1/2 rebase: use test_commit helper in setupJohn Cai via GitGitGadget, Mar 18, 2022
  39. Junio C HamanoMar 18, 2022
  40. 2/2 rebase: set REF_HEAD_DETACH in checkout_up_to_date()John Cai via GitGitGadget, Mar 18, 2022
  41. Junio C HamanoMar 18, 2022

Read the whole thread, see it on lore, or plain text.

$ cat FOOTERMessages come from the public archive at lore.kernel.org/git, fetched every hour. The front page is chosen and written each morning by an AI editor and can be wrong; the threads themselves are the record. About and API. For agents: an MCP server at https://gitlist.dev/mcp, and any thread, story or person page as Markdown by adding .md to its URL (or sending Accept: text/markdown). Details in /llms.txt.