Get SHA of parent by its ID

[Wirone]

I am trying to create script for linearizing repo (convert merge commits to "regular commit" by modifying parents information). I was able to do that, but since merge commits are automated in our project, their authorship comes from bot. For blame purposes (historical context) I would like to use authorship from 2nd parent (last commit of the merged branch), however --commit-callback receives commit objects that only have parents' IDs (integers), not SHAs, so I can't retrieve the author. I can't find the way to access _orig_graph (I see that the tool itself uses it for converting ID to hash like self._orig_graph.map_to_hash(old_id)). Is there a way to get parent's SHA?

[Wirone]

For those interested, I was able to make a PoC of this approach that is working on simple example repo, I am yet to verify it on actual repository. Here's the gist, maybe someone will find it helpful 🙂.