Determining whether you have a commit locally, in a partial clone?

[Tao Klerks <tao@klerks.biz>]

Hi folks,

I "discovered" today that when you're in a partial clone, naive tests
to check for whether you have a commit locally no longer work - they
fetch the commit on-demand:

git cat-file -t SOME_HASH_NOT_IN_REFSPEC
git rev-list SOME_HASH_NOT_IN_REFSPEC

I didn't realize this until today: even commits can be "filtered out"
by partial clone, so any reference to a commit that is not found
locally must be resolved transparently via jit-fetch.

I'm optimizing some stuff for users, so I need to know whether a given
commit exists locally or not... but I can't seem to figure out how!

I tried using "git rev-list"'s "--exclude-promisor-objects" option,
but I guess I don't understand what that's supposed to do. In my case
it just made a simple check like "git rev-list
--exclude-promisor-objects SOME_HASH_NOT_IN_REFSPEC" take forever (10
mins and counting).

I confirmed that removing (commenting out) the
"remote.origin.promisor" and "remote.origin.partialclonefilter" config
keys achieves my objective, but I can't figure out how to do it
safely; "-c remote.origin.promisor=false -c
remote.origin.partialclonefilter=" does *not* seem to work. The
existence of a "remote.origin.partialclonefilter" value, even if it is
empty, appears to override the "remote.origin.promisor=false" setting.

As far as I can tell, config values cannot be unset with "-c" - in
fact I see that credential.helper was granted special support for
empty string as a way of signalling "no credential helper" by Jeff
King in 2016.

So I guess I have two questions:
* Is there any way to run a single git command in a "don't use
promisors" context?
* Is the fact that "-c remote.origin.partialclonefilter=" doesn't work
for temporarily unsetting the filter a bug/issue to be resolved?

Thanks,
Tao