Re: [PATCH] t: avoid sed-based chain-linting in some expensive cases

["Martin Ågren" <martin.agren@gmail.com>]

On Fri, 14 May 2021 at 07:48, Jeff King <peff@peff.net> wrote:
>
> On Thu, May 13, 2021 at 01:05:28PM +0200, Martin Ågren wrote:
>
> > Devil's advocate: Who do we expect to turn GIT_TEST_CHAIN_LINT_HARDER
> > on, and when?  If no one ever does it then we might as well drop the
> > "default" thing and just go "we won't bother linting these particular
> > tests, ever". But as long as "someone" does it "sometimes", it's not
> > like it's a very complex mechanism to carry around.
>
> The answer is probably: people who suspect something is broken. We could
> perhaps also turn it on for CI to be more complete there (and where 30
> seconds of CPU time is relatively much smaller). It was also handy to
> have while timing the impact, of course.
>
> I'm not opposed to having it be less flexible, and in fact I wrote it

And to be clear, I'm not opposed to having it more flexible. :)

> that way originally. But it doesn't actually make the code much simpler.
> The assignments to _DEFAULT in the scripts become GIT_TEST_CHAIN_LINT_HARDER
> and the read side has one less level of defaulting:
>
> -test "${GIT_TEST_CHAIN_LINT_HARDER:-${GIT_TEST_CHAIN_LINT_HARDER_DEFAULT:-1}}" != 0 &&
> +test "${GIT_TEST_CHAIN_LINT_HARDER:-1}" != 0 &&
>
> I guess it's conceptually a little simpler, though. I dunno. I sort of
> assumed it would just work and nobody would need to ever look at or
> configure it either way. :)

:)

> > I seem to have 140 tests that haven't changed on disk since I did this
> > particular clone in 2017. 235 haven't changed this calendar year. Maybe
> > we could skip linting those tests that haven't been modified for several
> > weeks on the basis that they can't reasonably have newly-introduced
> > syntax mistakes. I guess it gets tricky where the t????-*.sh file
> > doesn't change in a long time, but it sources tests from other places,
> > such as a lib-foo.sh helper. We'd have to be a bit more clever there.
> > That's all just thinking out loud, and definitely not something that
> > should hold up your patch.
>
> Yeah, I suspect that would work in general. But it seems like even more
> complexity (now you have a cache of "I linted this script at time X and
> it was good" that has to be written). It does increase the possible
> savings though (up to perhaps 100 or so seconds of parallel CPU in my
> case).

Yeah, I thought about the cache. I guess it would be a list of
known-good test script hashes / blob IDs. But what I actually meant was
to check whether the mtime was way back in the past. It's not fool-proof
though. You could have a network-mounted disk where the date is way off,
or you could hack up the test script, wait for several weeks and *then*
run it. ;)

> I think a bigger and better version of that is to actually see which
> code paths are run by which scripts, and not even bother running scripts
> that don't touch code which has changed. But that's a _lot_ more
> complicated, and writing such a tool is probably at least worth a thesis
> project. ;)

Ah yes, it should be safe to punt on that for now.

Martin