Re: [PATCH v5 3/3] core: convert build-time USE_NSEC into runtime core.useNanosec

[Patrick Steinhardt <ps@pks.im>]

On Sun, Aug 30, 2026 at 08:27:13PM -0400, D. Ben Knoble wrote:
> On Sun, Aug 30, 2026 at 5:15 PM Junio C Hamano <gitster@pobox.com> wrote:
> >
> > "D. Ben Knoble" <ben.knoble@gmail.com> writes:
> >
> > > +             /* nanosecond timestamped files can also be racy! */
> > > +             (repo_config_values(istate->repo)->use_nanosec
> > > +              ? (istate->timestamp.sec < sd->sd_mtime.sec ||
> > > +                 (istate->timestamp.sec == sd->sd_mtime.sec &&
> > > +                  istate->timestamp.nsec <= sd->sd_mtime.nsec))
> > > +              : istate->timestamp.sec <= sd->sd_mtime.sec));
> > >  }
> >
> > Currently this is probably fine, but the use of repo_config_values()
> > here means that the order in which we can transition/libify two
> > unrelated things are forced on us:
> >
> >  * We'd first need to make sure repo_config_values() can work on an
> >    instance of repository that is not the_repository,
> >
> >  * And until the above happens, we cannot do a --recurse-submodule
> >    option that loads the index in a submodule and operate on it in
> >    the same process (e.g., "git diff --resurse-submodules"),
> >    because immediately at this step, istate taken from a submodule
> >    would have its .repo member pointing at something that is not
> >    the_repository and we will hit a BUG().
> >
> > And after writing all of the above, I realized that I am mostly
> > repeating what Patric already said in the upstream, e.g.,
> >
> >     https://lore.kernel.org/git/an720tZnot07HYiK@pks.im/
> 
> Yep---just so I'm clear, we don't currently have such an option,
> right? I mean, there is no --recurse-submodules for git-diff(1), and I
> tweaked t4060 to run "git -c core.useNanosec=true diff
> --submodule=diff" without any issue.

I do have a patch series coming up where we start to rely more on
sub-repositories when recursing. The motivation behind that series is
that it allows us to get rid of registering submodule object databases
with the main ODB. But I just double-checked, and your series luckily
doesn't break it.

> I would happily prove that at least none of our existing tests fail
> with core.useNanosec=true, but I'm not really sure how to shove
> configuration into every test invocation of git. Even if we could, I'm
> not sure we necessarily want to add another CI job for that (though
> that's a separate matter).
> 
> In particular, (among others) I have not received any concrete comments for
> 
> > Comments welcome: I haven't touched any tests; I saw a bunch of hits for
> > "git grep racy t" but wasn't sure how to fit this particular change in,
> > especially since it won't be equally valid on all systems? Advice
> > welcome.
> 
> so if there's at least a way to exercise this path on all the tests on
> my system (which should support it), that would probably be a good
> thing.

Yeah, I simply don't have a good answer here. It's messy, and I'm not a
fan of the current direction of `repo_config_values()` because nobody
has yet stepped up to untangle it from `the_repository`. I gave it a
quick shot at one point in time, but the result was messy at best
because of how we populate it via `repo_config(git_default_config)`.

In any case, if we see that your changes interact badly with some edge
cases that we don't currently have on our radar then we can still
refactor the series and move the value into `struct repo_settings`
instead, as that structure works alright with different repositories.

Thanks!

Patrick