Re: [RFC PATCH] repo-settings: set defaults even when not in a repo

["Ævar Arnfjörð Bjarmason" <avarab@gmail.com>]

On Tue, Mar 29 2022, Taylor Blau wrote:

> On Tue, Mar 29, 2022 at 11:04:18AM +0200, Ævar Arnfjörð Bjarmason wrote:
>>
>> On Wed, Mar 23 2022, Taylor Blau wrote:
>>
>> > On Wed, Mar 23, 2022 at 03:22:13PM -0400, Derrick Stolee wrote:
>> >> On 3/23/2022 2:03 PM, Josh Steadmon wrote:
>> >> > prepare_repo_settings() initializes a `struct repository` with various
>> >> > default config options and settings read from a repository-local config
>> >> > file. In 44c7e62 (2021-12-06, repo-settings:prepare_repo_settings only
>> >> > in git repos), prepare_repo_settings was changed to issue a BUG() if it
>> >> > is called by a process whose CWD is not a Git repository. This approach
>> >> > was suggested in [1].
>> >> >
>> >> > This breaks fuzz-commit-graph, which attempts to parse arbitrary
>> >> > fuzzing-engine-provided bytes as a commit graph file.
>> >> > commit-graph.c:parse_commit_graph() calls prepare_repo_settings(), but
>> >> > since we run the fuzz tests without a valid repository, we are hitting
>> >> > the BUG() from 44c7e62 for every test case.
>> >> >
>> >> > Fix this by refactoring prepare_repo_settings() such that it sets
>> >> > default options unconditionally; if its process is in a Git repository,
>> >> > it will also load settings from the local config. This eliminates the
>> >> > need for a BUG() when not in a repository.
>> >>
>> >> I think you have the right idea and this can work.
>> >
>> > Hmmm. To me this feels like bending over backwards in
>> > `prepare_repo_settings()` to accommodate one particular caller. I'm not
>> > necessarily opposed to it, but it does feel strange to make
>> > `prepare_repo_settings()` a noop here, since I would expect that any
>> > callers who do want to call `prepare_repo_settings()` are likely
>> > convinced that they are inside of a repository, and it probably should
>> > be a BUG() if they aren't.
>>
>> I think adding that BUG() was overzelous in the first place, per
>> https://lore.kernel.org/git/211207.86r1apow9f.gmgdl@evledraar.gmail.com/;
>
> I think Junio raised a good point in
>
>     https://lore.kernel.org/git/xmqqcznh8913.fsf@gitster.g/
>
> , though some of the detail was lost in 44c7e62e51 (repo-settings:
> prepare_repo_settings only in git repos, 2021-12-06).
>
>> I have that in my local integration branch, because I ended up wanting
>> to add prepare_repo_settings() to usage.c, which may or may not run
>> inside a repo (and maybe we'll have that config, maybe not).
>
> I see what you're saying, though I think we would be equally OK to have
> a default value of the repo_settings struct that we could rely on. I
> said some of this back in
>
>     https://lore.kernel.org/git/Yjt6mLIfw0V3aVTO@nand.local/
>
> , namely the parts around "I would expect that any callers who do want
> to call `prepare_repo_settings()` are likely convinced that they are
> inside of a repository, and it probably should be a BUG() if they
> aren't."
>
> Thinking in terms of your message, though, I think the distinction (from
> my perspective, at least) is between (a) using something called
> _repo_-settings in a non-repo context, and (b) calling a function which
> is supposed to fill in its values from a repository (which the caller
> implicitly expects to exist).
>
> Neither feel _good_ to me, but (b) feels worse, since it is making it OK
> to operate in a likely-unexpected context with respect to the caller's
> expectations.

I agree that it's a bit iffy. I'm basically advocating for treating
"the_repository->settings" as though it's a new "the_config" or
whatever.

Maybe we'd be better off just making that move, or having
the_repository->settings contain only settings relevant to cases where
we only have a repository.

But I think predicating useful uses of it on that refactoring is
overdoing it a bit, especially as I think your "(b)" concern here is
already something we deal with when it comes to
initialize_the_repository() and checks for
"the_repository->gitdir".

Can't we just have callers that really care about the distinction check
"->gitdir" instead? As they're already doing in some cases already?

Or just:

    git mv {repo,global}-settings.c

Since that's what it seems to want to be anyway.

> Anyway, I think that we are pretty far into the weeds, and it's likely
> time to turn around. I don't have that strong a feeling either way, and
> in all honesty either approach is probably just fine.

*nod*