Re: [RFC PATCH] t/Makefile: use dependency graph for "check-chainlint"

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

On Tue, Dec 14 2021, Eric Sunshine wrote:

> On Mon, Dec 13, 2021 at 5:09 AM Ævar Arnfjörð Bjarmason
> <avarab@gmail.com> wrote:
>> On Mon, Dec 13 2021, Eric Sunshine wrote:
>> > Rather than running `chainlint` and `diff` once per self-test -- which
>> > may become expensive as more tests are added -- instead run `chainlint`
>> > a single time over all tests bodies collectively and compare the result
>> > to the collective "expected" output.
>>
>> I think that "optimizing" things like this is an anti-pattern. I.e. we
>> have N chainlint test files, and N potential outputs from that (ok or
>> not, and with/without error). If one of the chainlint tests changes
>> we'd like to re-run it, if not we can re-use an earlier run.
>
> As mentioned in a reply elsewhere, the commit message sells this as an
> optimization, but that's not the real reason for the change, which is
> that the rewritten `check-chainlint` target for the upcoming new
> chainlint really wants to have a composite file of the "test" input
> and a composite of the "expect" output. I didn't know how to sell that
> change in this preparatory patch series, so I weakly framed it as an
> optimization. The reason for making this a preparatory step is that it
> makes for a less noisy patch later on when the new chainlint is
> actually plugged into the `check-chainlint` target. At least, it was
> less noisy originally... in the final implementation, I think it ends
> up being noisy anyhow. So, maybe it makes sense to drop this patch
> altogether(?).

I think you should do whatever you think makes sense here, I was just
pointing out that alternate Makefile approach in case it was helpful.

>> This is something make's dependency logic is perfectly suited for, and
>> will be faster than any optimization of turning a for-loop into a
>> "sed" command we run every time, since we'll only need to "stat" a few
>> things to see that there's nothing to do.
>>
>> +BUILT_CHAINLINTTESTS = $(patsubst %,.build/%.actual,$(CHAINLINTTESTS))
>> +
>> +.build/chainlint:
>> +       mkdir -p $@
>> +
>> +$(BUILT_CHAINLINTTESTS): | .build/chainlint
>> +$(BUILT_CHAINLINTTESTS): .build/%.actual: %
>> +       $(CHAINLINT) <$< | \
>> +       sed -e '/^# LINT: /d' >$@ && \
>> +       diff -u $(basename $<).expect $@
>> +
>> +check-chainlint: $(BUILT_CHAINLINTTESTS)
>
> This sort of optimization makes sense (I think) even with the new
> chainlint preferring to see composite "test" and "expect" files rather
> than the individual files. The individual files would be prerequisites
> of the composite files, thus the composites would only be regenerated
> if the individual files change. And the composite files would be
> prerequisites of the `check-chainlint` target, so it would only run if
> the composite files change (or if chainlint itself changes).
>
> In fact, with the new chainlint checking all tests in all scripts at
> once, this technique should apply nicely to it, as well, since the
> names of test scripts (t????-*.sh) are fed to it as command-line
> arguments. Thus, the t????-*.sh files could be prerequisites of the
> chainlint rule which would use $? to check only test scripts which
> have changed since the previous run.

*nod*

> Having said all that, I don't think think the changes in this series
> or the upcoming new chainlint series make the situation any worse
> (Makefile-wise) than its current state, and the sort of optimizations
> discussed here can easily be made after those series land. (And, as my
> Git time is rather limited these days, I'd really like to focus on
> getting the core components landed.)

Sounds good to me. We have plenty of these "doesn't have deps" targets
(e.g. the check shell syntax one you noted), we can just fix/change them
some other time.