history: 'reword HEAD' surfaces a memory leak

["Kristoffer Haugsbakk" <kristofferhaugsbakk@fastmail.com>]

I get a sanitizer error when I run a simple reword command:

    $ make SANITIZE=address install
    $ GIT_EDITOR=true git history reword \
        --dry-run 3cb9185f65410273787f74333cc027d2ea5daada
    update HEAD eeb9d4b5c4041739c0a19b4043924513c8aad2d2 3cb9185f65410273787f74333cc027d2ea5daada

    =================================================================
    ==116999==ERROR: LeakSanitizer: detected memory leaks

    Direct leak of 283 byte(s) in 1 object(s) allocated from:
        #0 0x712d2f6b4887 in __interceptor_malloc ../../../../src/libsanitizer/asan/asan_malloc_linux.cpp:145
        #1 0x61970a5757b2 in do_xmalloc /home/kristoffer/programming/git-worktree/git-leakcheck/wrapper.c:55
        #2 0x61970a575ec0 in do_xmallocz /home/kristoffer/programming/git-worktree/git-leakcheck/wrapper.c:89
        #3 0x61970a575ec0 in do_xmallocz /home/kristoffer/programming/git-worktree/git-leakcheck/wrapper.c:79
        #4 0x61970a575ec0 in xmallocz_gently /home/kristoffer/programming/git-worktree/git-leakcheck/wrapper.c:102
        #5 0x61970a309ca0 in unpack_compressed_entry /home/kristoffer/programming/git-worktree/git-leakcheck/packfile.c:1732
        #6 0x61970a310bf0 in unpack_entry /home/kristoffer/programming/git-worktree/git-leakcheck/packfile.c:1885
        #7 0x61970a311fbf in cache_or_unpack_entry /home/kristoffer/programming/git-worktree/git-leakcheck/packfile.c:1528
        #8 0x61970a311fbf in packed_object_info_with_index_pos /home/kristoffer/programming/git-worktree/git-leakcheck/packfile.c:1610
        #9 0x61970a313097 in packed_object_info /home/kristoffer/programming/git-worktree/git-leakcheck/packfile.c:1720
        #10 0x61970a313097 in packfile_store_read_object_info /home/kristoffer/programming/git-worktree/git-leakcheck/packfile.c:2214
        #11 0x61970a2caae8 in odb_source_files_read_object_info odb/source-files.c:58
        #12 0x61970a2c69a7 in odb_source_read_object_info odb/source.h:326
        #13 0x61970a2c69a7 in do_oid_object_info_extended /home/kristoffer/programming/git-worktree/git-leakcheck/odb.c:572
        #14 0x61970a2c69a7 in odb_read_object_info_extended /home/kristoffer/programming/git-worktree/git-leakcheck/odb.c:710
        #15 0x61970a2c7cbe in odb_read_object /home/kristoffer/programming/git-worktree/git-leakcheck/odb.c:756
        #16 0x61970a101d5a in repo_get_commit_buffer /home/kristoffer/programming/git-worktree/git-leakcheck/commit.c:399
        #17 0x61970a101d5a in repo_get_commit_buffer /home/kristoffer/programming/git-worktree/git-leakcheck/commit.c:391
        #18 0x61970a346bf6 in repo_logmsg_reencode /home/kristoffer/programming/git-worktree/git-leakcheck/pretty.c:716
        #19 0x619709ebbe64 in commit_tree_ext builtin/history.c:127
        #20 0x619709ebd17f in commit_tree_with_edited_message builtin/history.c:183
        #21 0x619709ebd17f in cmd_history_reword builtin/history.c:717
        #22 0x619709ec186f in cmd_history builtin/history.c:998
        #23 0x619709d87ca0 in run_builtin /home/kristoffer/programming/git-worktree/git-leakcheck/git.c:506
        #24 0x619709d87ca0 in handle_builtin /home/kristoffer/programming/git-worktree/git-leakcheck/git.c:782
        #25 0x619709d8c9a6 in run_argv /home/kristoffer/programming/git-worktree/git-leakcheck/git.c:865
        #26 0x619709d8c9a6 in cmd_main /home/kristoffer/programming/git-worktree/git-leakcheck/git.c:986
        #27 0x619709d83f54 in main /home/kristoffer/programming/git-worktree/git-leakcheck/common-main.c:9
        #28 0x712d2f229d8f in __libc_start_call_main ../sysdeps/nptl/libc_start_call_main.h:58

    SUMMARY: AddressSanitizer: 283 byte(s) leaked in 1 allocation(s).

The `--dry-run` is optional.

I get this on master, next, and seen, respectively:

1. `master`: 17ff1f98 (Sync with 'master', 2026-09-02)
2. 17ff1f98 (Sync with 'master', 2026-09-02)
3. 99855fed (Merge branch 'cc/early-scan-options' into seen, 2026-09-02)

I do not get this error when testing on the commit that introduced `git
history reword` (see later bisect log).

It’s too technical for me, but it seems that git-history(1) just
triggers a memory leak in the internal library (name?) code. Maybe you
need a packfile and/or a commit graph?

Bisecting told me that the first bad commit is 13763ecf (Merge branch
'ps/receive-pack-shallow-optim', 2026-03-02).

I tried to make an automated test for it but didn’t quite hack it. I got
an ad hoc repo to reproduce. Running a GC or commit-graph (and/or) might
have what have done it.

But it seems to happen every time I run the command in a “real repo” as
long as I don’t violate one of the preconditions (“can’t replay merge
commits yet!” etc.).

BISECT SCRIPT

Note: hopefully this isn’t sensitive to if there are
refs pointing to that commit. The commit is just
`git rev-parse origin/master`.

```
#!/bin/sh

# No setup. Just use this repo.
make SANITIZE=address || exit 125
: >err.txt
GIT_EDITOR=true ./bin-wrappers/git history reword 3cb9185f65410273787f74333cc027d2ea5daada 2>err.txt || {
    grep -q 'detected memory leaks' err.txt && exit 1
}

exit 0
```

BISECT LOG

    $ git bisect log
    git bisect start
    # status: waiting for both 'good' and 'bad' commits
    # bad: [1630431f326e15fcde608827b5ff38422528eb59] The 21st batch
    git bisect bad 1630431f326e15fcde608827b5ff38422528eb59
    # status: waiting for 'good' commit(s), 'bad' commit known
    # good: [d205234cb05a5e330c0f7f5b3ea764533a74d69e] builtin/history: implement "reword" subcommand
    git bisect good d205234cb05a5e330c0f7f5b3ea764533a74d69e
    # bad: [27caa6b4f7bce94fc1f07b96bcb0bcef8c5215f5] Merge branch 'en/backfill-fixes-and-edges'
    git bisect bad 27caa6b4f7bce94fc1f07b96bcb0bcef8c5215f5
    # bad: [6cdef943d28fa7d6964ec570b33a0bff4c80ea8c] Merge branch 'ps/odb-sources' into ps/object-counting
    git bisect bad 6cdef943d28fa7d6964ec570b33a0bff4c80ea8c
    # good: [94336d77bcbf4360b67a9454d8bf2e84b3d88ae7] Merge branch 'sd/doc-my1c-api-config-reference-fix'
    git bisect good 94336d77bcbf4360b67a9454d8bf2e84b3d88ae7
    # bad: [13763ecf7d92be72beff75c59163c5448d9e085e] Merge branch 'ps/receive-pack-shallow-optim'
    git bisect bad 13763ecf7d92be72beff75c59163c5448d9e085e
    # good: [bb9c781f4f4be2e6bf6285149ba7007fdaa735e7] Merge branch 'ps/history-ergonomics-updates'
    git bisect good bb9c781f4f4be2e6bf6285149ba7007fdaa735e7
    # good: [2cc71917514657b93014134350864f4849edfc83] The 8th batch
    git bisect good 2cc71917514657b93014134350864f4849edfc83
    # good: [664bd4e15a99a477acb616337df0f9fa95c729c3] Merge branch 'ty/symlinks-use-unsigned-for-bitset'
    git bisect good 664bd4e15a99a477acb616337df0f9fa95c729c3
    # good: [05c4af5c8f3d7310c8a3b2909d30ce761c6757aa] Merge branch 'kh/doc-am-xref'
    git bisect good 05c4af5c8f3d7310c8a3b2909d30ce761c6757aa
    # good: [427d39ca4f4f7a0e66652d92340af43cbda5135e] Merge branch 'ps/meson-gitk-git-gui'
    git bisect good 427d39ca4f4f7a0e66652d92340af43cbda5135e
    # good: [34113149cfde760b6b791939c6d8d87d27ca2767] Merge branch 'kh/doc-patch-id-4'
    git bisect good 34113149cfde760b6b791939c6d8d87d27ca2767
    # good: [024b4c96976fabdc8b73f4183d6bb8626ffe2c7d] commit: make `repo_parse_commit_no_graph()` more robust
    git bisect good 024b4c96976fabdc8b73f4183d6bb8626ffe2c7d
    # good: [bb5da75d6116c35924a04a418ef4c3182663d0a2] commit: use commit graph in `lookup_commit_reference_gently()`
    git bisect good bb5da75d6116c35924a04a418ef4c3182663d0a2
    # first 'bad' commit: [13763ecf7d92be72beff75c59163c5448d9e085e] Merge branch 'ps/receive-pack-shallow-optim'