Re: Crash on git log with -L and -G on file rename

> 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]