"Kristoffer Haugsbakk" [off-list ref] writes:

You can trigger an assertion by giving these arguments to `git mv`:

    <dir>/file <dir> <other dir>
...

quoted

What did you expect to happen? (Expected behavior)

A normal error message if the command is nonsensical (I don’t know; that’s
not the point). Also `.git/index.lock` to be cleaned up.

Good find.

Not just that, but when the command fails in the middle like this,
it leaves the working tree in a half-updated state, i.e.

./bin-wrappers/git -C $dir mv $dir/a/a.txt $dir/a $dir/b

will first move a/a.txt to b/a.txt, then try to move a (actually,
all contents of it, including a/a.txt) to b/a and finds that "the
command is nonsensical" and aborts, and by that time, there is no
a/a.txt (i.e. the working tree has been modified).  The failure
should be made atomic, just like "git switch" to another branch may
stop _without_ touching anything in the working tree when it may
have to fail (e.g., due to a file being dirty).

Thanks for reporting, Kristoffer.

Any takers?

$ git shortlog --since=3.years -s -n -e --no-merges v2.43.0 builtin/mv.c
    15	Shaoxuan Yuan [off-list ref]
    10	Elijah Newren [off-list ref]
     5	Ævar Arnfjörð Bjarmason [off-list ref]
     2	Junio C Hamano [off-list ref]
     1	Andrzej Hunt [off-list ref]
     1	Calvin Wan [off-list ref]
     1	Derrick Stolee [off-list ref]
     1	Sebastian Thiel [off-list ref]
     1	Torsten Bögershausen [off-list ref]