On Tue, Jul 22, 2025 at 03:23:05PM +0000, Elijah Newren via GitGitGadget wrote:

At GitHub, we've got a real-world repository that has been triggering
failures of the form:

git: merge-ort.c:3007: process_renames: Assertion `newinfo && !newinfo->merged.clean' failed.


Digging in, this particular corner case requires multiple things to trigger:
(1) a rename/delete of one file, and (2) a directory rename modifying an
unrelated rename such that this unrelated rename's target becomes the source
of the rename/delete from (1).

Unfortunately, looking around, it's not the only bug in the area. Plus, some
of our testcases in tangential situations were not checked closely enough or
were weird or buggy in various ways. Adding to the challenge was the fact
that the relevant renames optimization was sometimes triggering making
renames look like delete-and-add, and overlooking this meant I sometimes
wasn't triggering what I thought I was triggering.

The combination of challenges sometimes made me think my fixes were breaking
things when sometimes I was just unaware of other bugs. I went in circles a
few times and took a rather non-linear path to finding and fixing these
issues. While I think I've turned it into a nice linear progression of
patches, I might be a bit too deep in the mud and it might not be as linear
or clear as I think. Let me know and I'll try to clarify anything needed.

I had a read through this whole series and it looks plausible to me. I
won't claim to fully understand it though given that I don't have a lot
of experience with the whole merge machinery.

Patrick