Re: [PATCH 1/3] pack-objects: fix handling of multiple --filter options

[Jeff King <peff@peff.net>]

On Sat, Nov 12, 2022 at 11:44:00AM +0100, René Scharfe wrote:

> Since 5cb28270a1 (pack-objects: lazily set up "struct rev_info", don't
> leak, 2022-03-28) --filter options given to git pack-objects overrule
> earlier ones, letting only the leftmost win and leaking the memory
> allocated for earlier ones.  Fix that by only initializing the rev_info
> struct once.

Yikes. I wondered how we managed to miss this in the tests. Surely we
have some examples that use multiple filters?

I think the answer is that we do in t5616, but in practice they didn't
hit this bug because of the way filter-specs are treated server-sid3.
Even if we say "clone --filter=foo --filter=bar" on the client, the
server upload-pack coalesces that into a single "combine:foo+bar"
string, and that's what its pack-objects sees.

Your test here triggers it by invoking pack-objects directly, which
makes sense. That's a little different from how pack-objects is invoked
by the rest of Git in practice, but it's definitely something that
_should_ work. It's conceivable that somebody outside of Git could be
driving pack-objects directly, but also it's just a trap waiting to
spring for future developers.

-Peff