Re: [PATCH v3 6/6] Makefile: build "$(FUZZ_OBJS)" in CI, not under "all"

From: Jeff King <peff@peff.net>
Date: Feb 23, 2021, 18:28 UTC
Message-ID: <YDVJZnmTiBYZ4iPM@coredump.intra.peff.net>
In-Reply-To: <20210223114132.24345-7-avarab@gmail.com>

On Tue, Feb 23, 2021 at 12:41:32PM +0100, Ævar Arnfjörð Bjarmason wrote:

Show 10 quoted lines

> Adding $(FUZZ_OBJS) as a dependency on "all" was intentionally done in
> 5e472150800 (fuzz: add basic fuzz testing target., 2018-10-12).
> 
> Rather than needlessly build these objects which aren't required for
> the build every time we make "all", let's instead move them to be
> built by the CI jobs.
> 
> The goal is to make sure that we don't inadvertently break these, we
> can accomplish that goal by building them in CI, rather than slowing
> down every build of git for everyone everywhere.

The current state is that regular devs are responsible for avoiding compile breakages in the fuzz objects, even if they don't care themselves. Your earlier patches turned this into: regular devs are not on the hook for breaking fuzz objects; they are the responsibility of fuzz people. I'm OK with either of those, but this approach seems to me like the worst of both worlds. ;)

If you do a refactor, you are still on the hook for breaking the fuzz objects because CI will fail (and you have to investigate it, and fix it for CI to remain a useful tool). But instead of finding out about the problem quickly as you're working, instead you push up what you think is a finished result, and then from minutes to hours later you get a notification telling you that oops, you missed a spot. I find that the shorter the error-fix-compile cycle is, the less time I waste waiting or context-switching.

If we had a ton of fuzz object files that took forever to build, the savings on each build might be worth it. But AFAICT (from timing "make clean; make -j1" before and after), we are saving less than 1% of the build time (which is way less than the run-to-run noise).

It doesn't seem like the right tradeoff to me. (Likewise, if other CI-only checks we have, like coccinelle, could be run at a similar cost, I'd recommend sticking them into the default developer build).

One thing we _could_ do is stop building fuzz objects as part of "all", but include them for DEVELOPER=1 builds (which includes CI). That keeps them from hurting normal users (who don't actually need them), but prevents bitrot. It doesn't address your original motivation though (you as a developer would probably still be building them).

-Peff