Determining if a merge was produced automatically

Hello,

I'm looking for a robust way to determine if a given merge commit could've been produced automatically by `git merge`, without any manual intervention or tampering, such as:

  - resolving conflicts,
  - stopping (`--no-commit`) and modifying,
  - amending the commit.

My initial idea was to re-enact the merge. If the merge failed, I would conclude that the original merge couldn't have been produced automatically. If the merge succeeded, I would compare it with the original merge. Any differences would indicate that the original merge couldn't have been produced automatically. Otherwise, I would conclude that it could've been. This approach is simple, but involves multiple steps and requires clean-up.

My second idea was to use `git show --diff-merges=dense-combined`, which only prints hunks that come from neither parent. If nothing is printed, I would conclude that the merge could've been produced automatically. This approach is simple, single-step, but seems to have an issue. In my experiments, I found that if some hunks from different parents were located closely enough, output was produced. So, checking if nothing is output could lead to false negatives: a merge that could've been produced automatically might look like it was tampered with.

My third idea was to use a recently added feature, `git show --remerge-diff`, which seemingly embodies my first idea and is immune to the issue of the second. It is also single-step and requires no clean-up:

However, this bit means that I shouldn't entirely trust its output:

What is my best course of action?

Thanks, -Pavel