Re: Bug report for pull --rebase

From: D. Ben Knoble <ben.knoble@gmail.com>
Date: May 9, 2025, 16:41 UTC
Message-ID: <CALnO6CB6aH5DEDP3QL43RCFfaZJ3uzrAY1LdGyTNi8F3XVoEhw@mail.gmail.com>
In-Reply-To: <8c075e6e-c28c-4146-66bc-9bd7bc705611@gmail.com>

On Tue, May 6, 2025 at 5:44 PM Mr Bill <billc56196@gmail.com> wrote:

Show 28 quoted lines

>
>
> Hi, I ran across this doing a pull --rebase using the current master
> version of git
>
> This happens on Slackware linux, using git HEAD, version 2.35.8, and 2.46.2
>
> I have a clone of the ffmpeg video package, with a few custom commits on
> top of it,
> I periodically fetch and "pull --rebase" to update the underlying ffmpeg
> code.
> I tried this recently, and my custom commits disappeared.
>
>
> I looked further with a small test, and it looks like this is happening:
>
> The setup:
>     "base" repo with a few commits (A, B, C)
>     "clone_1" cloned from "base", with a few extra commits (F, G)
>     "clone_2" cloned from "clone_1"
>
> Add a few more commits for base (D, E)
>
> Then use "git remote set-url origin" to point "clone_2" to "base"
>
> Then, in "clone_2" do "pull --rebase"; the F and G commits disappear.
>
> Then, in "clone_1" do "pull --rebase"; the F and G commits are retained.

Thanks for including a script! I modified it (uploaded to https://gist.github.com/benknoble/7a5eecd522b48669c2a5207e2ed9b7ee to avoid problems with my mailer) to be suitable for use with bisect.

I put the script at /tmp/bugreport/doit next to a clone of the Git source code, then (in the Git source repo) started a --first-parent bisect between 2.49 and 2.0 with the ../doit script as the runner; here's the log:

# bad: [683c54c999c301c2cd6f715c411407c413b1d84e] Git 2.49 # good: [e156455ea49124c140a67623f22a393db62d5d98] Git 2.0 git bisect start '--first-parent' '@' 'v2.0.0' # bad: [4336fdb2efaf77b720f152c06b5ce2aa2e347fb6] Merge branch 'rs/nedalloc-fixlets' git bisect bad 4336fdb2efaf77b720f152c06b5ce2aa2e347fb6 # bad: [130b664e442767587638b3e807a6f543168239d7] Merge branch 'js/travis-32bit-linux' git bisect bad 130b664e442767587638b3e807a6f543168239d7 # bad: [922239e7da03f8e0a8c6ba809c1ee0cf3776f94a] Merge branch 'dk/p4-import-ctypes' git bisect bad 922239e7da03f8e0a8c6ba809c1ee0cf3776f94a # bad: [afa3ccbf44cb47cf988c6f40ce3ddb10829a9e7b] Merge branch 'jc/pretty-format-doc' git bisect bad afa3ccbf44cb47cf988c6f40ce3ddb10829a9e7b # bad: [7669461459aaee1587bac77c4a446e9365b582c7] Merge branch 'rs/merge-tree-simplify' git bisect bad 7669461459aaee1587bac77c4a446e9365b582c7 # bad: [3d77f72efe79eb90f67aec9ecf6d4bd11fc9a78c] Merge branch 'jc/fix-clone-single-starting-at-a-tag' git bisect bad 3d77f72efe79eb90f67aec9ecf6d4bd11fc9a78c # bad: [5b3a58d459171f49ee8d486e4ac399eb2678605d] Merge branch 'jk/argv-array-for-child-process' git bisect bad 5b3a58d459171f49ee8d486e4ac399eb2678605d # bad: [d83c9c75e1edebd4ece3ad5223103f46fc38a4d3] Merge branch 'jk/grep-tell-run-command-to-cd-when-running-pager' git bisect bad d83c9c75e1edebd4ece3ad5223103f46fc38a4d3 # bad: [e3798318b12502ae13a8e35e4a385665e810047f] Merge branch 'mm/mediawiki-encoding-fix' git bisect bad e3798318b12502ae13a8e35e4a385665e810047f # bad: [2e4b5dee97cb1524a88f0ee90450b139bfaff07b] Merge branch 'rs/ref-update-check-errors-early' git bisect bad 2e4b5dee97cb1524a88f0ee90450b139bfaff07b # bad: [f008cef4abb2a4db766b4a152b304aca91a0101a] Merge branch 'jc/apply-ignore-whitespace' git bisect bad f008cef4abb2a4db766b4a152b304aca91a0101a # bad: [bce14aa132e0064d9a9b1c7ad98e71e22c6e0272] Sync with 1.9.4 git bisect bad bce14aa132e0064d9a9b1c7ad98e71e22c6e0272 # bad: [d7172825321369cb951dd7bbfc0c12dc4ecbe518] t5537: re-drop http tests git bisect bad d7172825321369cb951dd7bbfc0c12dc4ecbe518 # first bad commit: [d7172825321369cb951dd7bbfc0c12dc4ecbe518] t5537: re-drop http tests

I think this just means the bug has been present since at least 2.0 (I never checked if 2.0 was actually "good"; that was just as far back as I was willing to go).

I didn't try to track down where it came from, though.

P.S. I was having trouble building master (something in the linker with _false_but_the_compiler_does_not_know_it)? Revision 1ee85f0e21 (The twelfth batch, 2025-05-08). Log at https://gist.github.com/benknoble/a8bdc272f44673e115f8b3e57d62e4f6. P.P.S. I was flummoxed for a long time before I realized that "git bisect run" sets GIT_DIR in the environment (checked by comparing the script's environment in and out of "git bisect run"); is that documented? Intended? Made it harder to drive Git in this script (see "unset GIT_DIR").

-- 
D. Ben Knoble