Re: [PATCH v3 0/4] cache parent project's gitdir in submodules

On Thu, Aug 19, 2021 at 09:09:46PM -0400, Derrick Stolee wrote:

On 8/19/2021 4:09 PM, Emily Shaffer wrote:

quoted

Since v2, mostly documentation changes and a handful of small nits from
Junio and Jonathan Tan. Thanks for the reviews, both.

Sorry to show up late with many questions (mostly because my understanding
of submodules is not as strong as yours),

Well, here I am apologizing for showing up even later with a reply ;)

but I do have some concerns that
we have not covered all the cases that could lead to the relative path
needing an update, such as a 'git checkout' across commits in the super-
project which moves a submodule.

Leading more to my confusion is that I thought 'git submodule update'
was the way to move a submodule, but that does not appear to be the case.
I used 'git mv' to move a submodule and that correctly updated the
.gitmodules file, but did not run any 'git submodule' subcommands (based
on GIT_TRACE2_PERF=1).

During a live review a few weeks ago it was pointed out, I forget by
who, that this whole series would make a lot more sense if it was
treated as the path from the submodule's gitdir to the superproject's
gitdir. I think this would also fix your 'git mv' example here, as the
submodule gitdir would not change.

You mention in an earlier cover letter that this config does not need to
exist, but it seems to me that if it exists it needs to be correct for us
to depend on it for future features. I'm not convinced that we can rely
on it as-written, but you might be able to convince me by pointing out
why these submodule movements are safe.

Yeah, that is a good point, and I wonder how to be defensive about
this... Maybe it makes sense to BUG() if we don't find the
superproject's gitdir from this config? Maybe it makes sense to warn
(asking users to 'git submodule update') and erase the incorrect config
line?

Both those approaches would require a wrapper around
'git_config_get_string()' to cope with a failure, but it might be worth
it.

I'll try proposing such a wrapper in the reroll, unless I hear back
sooner.

 - Emily