From: Koji Nakamaru <koji.nakamaru@gree.net>
Date: Wed, 04 Mar 2026 03:01:54 GMT
Subject: Re: Crash on git log with -L and -G on file rename
Message-ID: <CAOTNsDwdS=+4RuAD6pAt-==uE6S4Wq_4cat+0OqmKV2wgoVheQ@mail.gmail.com>
In-Reply-To: <aac-QdjY1ohAqgw_@desktop>

On Wed, Mar 4, 2026 at 5:42 AM Matthew Hughes
<matthewhughes934@gmail.com> wrote:
>
> Hi,
>
> I hit a crash (assertion error) running `git log` with both `-L` and `-G` under
> certain conditions. I've created script to reproduce the behaviour in a fresh
> git repo:
>
>     #!/usr/bin/env bash
>
>     set -o errexit
>
>     git init .
>     # Note: example is .rs file, but it should work with anything that -L understands
>     echo "fn my_func() {}" > file.rs
>     # 1. file named 'file.rs'
>     git add file.rs
>     git commit --message 'Add the file'
>
>     # 2. separate branch with the file renamed
>     git checkout -b some-branch
>     git mv file.rs new_file.rs
>     git commit --message 'Move the file'
>
>     git checkout -
>     git commit --allow-empty --message 'Some extra commit so we get a merge commit'
>     # 3. merge: one parent has file.rs, the other has new_file.rs
>     git merge --no-edit some-branch
>
>     # 4. post merge, move the file back
>     git mv new_file.rs file.rs
>     git commit --message 'Move the file back'
>
>     # 5. things go BOOM
>     git log -L:my_func:file.rs -G '.'
>
> I'm not sure if _every_ step in that script is necessary, but it's the simplest
> setup I could figure out to trigger the crash. Running that script I hit the
> error:
>
>     git: line-log.c:1056: process_diff_filepair: Assertion `pair->two->oid_valid' failed.
>     Aborted                    (core dumped) git log -L:my_func:file.rs -G '.'
>
> The backtrace shows that the failed assertion occurs under
> `process_ranges_merge_commit`, so maybe there's an issue with the file being
> renamed on both sides of the merge?
>
> The crash requires both flags to trigger, remove either and it will run fine.
>
> I've tested the above on the `git` from my system package manager on Arch
> Linux: git version 2.53.0, and one built from source at
> 2cc71917514657b93014134350864f4849edfc83 (the version of 'master' checked out
> on my machine at the time). I don't think reproduction relies on any specific
> config since I've had it trigger with both `GIT_CONFIG_GLOBAL` and
> `GIT_CONFIG_SYSTEM` set to `/dev/null`
>
> Just for reference, I originally triggered the bug in the `rustfmt` repo[1]
> (checked-out at cebab3e99259be82ff069e5ae89e91855d79e534) running:
>
>     git log -G offset_left -L:format_trait:src/items.rs
>
> Link: github.com/rust-lang/rustfmt [1]
>

The root cause appears to be that diff_might_be_rename() only checks
diff_queued_diff.queue[i]->one. The following change can fix the issue.

diff --git a/line-log.c b/line-log.c
index eeaf68454e..2da7658ba9 100644
--- a/line-log.c
+++ b/line-log.c
@@ -834,6 +834,10 @@ static inline int diff_might_be_rename(void)
            /* fprintf(stderr, "diff_might_be_rename found creation
of: %s\n", */
            /*  diff_queued_diff.queue[i]->two->path); */
            return 1;
+       } else if (!DIFF_FILE_VALID(diff_queued_diff.queue[i]->two)) {
+           /* fprintf(stderr, "diff_might_be_rename found deletion
of: %s\n", */
+           /*  diff_queued_diff.queue[i]->one->path); */
+           return 1;
        }
    return 0;
 }

--
Koji Nakamaru