2 conflicts referencing the same path?

From: Bryan Turner <bturner@atlassian.com>
To: Git Users <git@vger.kernel.org>
Subject: 2 conflicts referencing the same path?
Date: Thu, 1 Feb 2018 15:00:40 -0800	[thread overview]
Message-ID: <CAGyf7-He4in8JWUh9dpAwvoPkQz9hr8nCBpxOxhZEd8+jtqTpg@mail.gmail.com> (raw)

While investigating an issue with rendering conflicts on a pull
request, I noticed that the merge was producing this output (sanitized
for paths)

$ git merge --no-ff --log -m "Test" 190a25b6e0f32c7b8ccddf8c31e054149dece8b7
CONFLICT (rename/add): Rename A->B in HEAD. B added in
190a25b6e0f32c7b8ccddf8c31e054149dece8b7
Adding as B~190a25b6e0f32c7b8ccddf8c31e054149dece8b7 instead
...
Auto-merging B
CONFLICT (content): Merge conflicts in B

(There are several other conflicts listed "between" the two I'm
showing here, various rename/add, add/add and content conflicts, but
I'm trimming those out to focus on the lines that I think are relevant
to my question.)

This merge produces 2 (or is it 3?) conflicts for the same B path:
- Rename A to B in HEAD, add B in 190a25b
- Content conflicts in B

The version of B left in place _does_ contain conflict markers, after
the merge processes completes. The version added as B~190a25b has no
conflict markers; it just shows a small number of inserted lines.

The merge in question produces 23 different CONFLICT lines, but aside
from "composite" conflicts (rename/add, add/add) that can include the
same path multiple times in their output, only this one path is
mentioned in multiple CONFLICT lines.

I'm still trying to produce a set of steps that will allow a minimal
reproduction, but I thought I'd post to the list just to see if anyone
had any thoughts on how it could happen. Is it a "normal" (albeit
rare) case? Or could it represent some sort of issue in Git's 3-way
merge algorithm (in its behavior or perhaps in how the merge conflicts
are logged)?

Any insights appreciated!
Bryan Turner