Re: [PATCH v2 3/5] tests: turn GPG, GPGSM and RFC1991 into lazy prereqs

From: Johannes Schindelin <johannes.schindelin@gmx.de>
Date: Mar 30, 2020, 18:39 UTC
Message-ID: <nycvar.QRO.7.76.6.2003302027240.46@tvgsbejvaqbjf.bet>
In-Reply-To: <20200327091004.GA610157@coredump.intra.peff.net>

Hi Peff,

On Fri, 27 Mar 2020, Jeff King wrote:

Show 13 quoted lines

> On Thu, Mar 26, 2020 at 03:27:19PM +0100, Johannes Schindelin wrote:
>
> > > OK. This looks good, even if I cannot help feel that my earlier patch
> > > was perfectly sufficient. ;)
> >
> > The mistake is all mine. I had totally missed that you turned GPG into a
> > lazy prereq. So I had my patch finalized already before you pointed my
> > nose at that fact.
> >
> > Sorry about that.
>
> No problem. And I hope my review didn't sound too passive-aggressive
> with the "well, in MY version we did this...".

FWIW I failed to interpret anything in your reply as passive-aggressive, probably because I am just too used to receive competent, helpful and friendly replies from you.

> I focused on the differences because those were the parts that were new
> (and therefore interesting) to me. But I don't think any of them are too
> important either way.

To me, it all sounded like a constructive discussion we had, and since you already had a working patch that did something very similar to mine, it made sense to look at their differences.

Show 22 quoted lines

> > - Since this code is outside of a function, `return` felt like the wrong
> >   semantic concept to me. And indeed, I see this (rather scary) part in
> >   Bash's documentation of `return` (I did not even bother to look at the
> >   POSIX semantics, it scared me so much):
> >
> >       The return status is non-zero if `return` is supplied a non-numeric
> >       argument, or is used outside a function and not during execution of
> >       a script by `.` or `source`.
> >
> >   So: the `1` is totally ignored in this context. That alone is reason
> >   enough for me to completely avoid it, and use `exit` instead.
>
> I agree the portability rules there are scary, but none of that applies
> because we _are_ in a function: test_eval_inner_(). This behavior is
> intentional and due to a7c58f280a (test: cope better with use of return
> for errors, 2011-08-08). I thought we specifically advertised this
> feature in t/README, but I can't seem to find it.
>
> So my perspective was the opposite of yours: "return" is the officially
> sanctioned way to exit early from a test snippet, and "exit" only
> happens to work because of the undocumented fact that lazy prereqs
> happen in a subshell. But it turns out neither was documented. :)

Can a subshell inside a function cause a `return` from said function? I don't think so, but let's put that to a test:

	function return_from_a_subshell () {
		echo before
		(echo subshell; return; echo unreachable)
		echo after $?
	}

Let's run that.

	$ return_from_a_subshell
	before
	subshell
	after 0

To me, the fact that that `return` does not return from the function, but only exits the subshell, in my mind lends more credence to the idea that `exit` is more appropriate in this context than `return`.

For shiggles, I also added that `$?` because I really, _really_ wanted to know whether my reading of GNU Bash's documentation was correct, and it appears I was mistaken: apparently `return` used outside a function does _not_ cause a non-zero exit code.

Show 18 quoted lines

> > > In mine I put the test_have_prereq outside the lazy prereq.
> >
> > That makes it essentially a non-lazy prereq.
> >
> > > I don't think it really matters either way (when we later ask if GPGSM
> > > is set, there is no difference between nobody having defined it, and
> > > having a lazy definition that said "no").
> >
> > The difference is when running a test with `--run=<n>` where `<n>` refers
> > to a test case that requires neither GPG nor GPGSM or RFC1991. My version
> > will not evaluate the GPG prereq, yours still will.
>
> Yes. Part of the reason I kept mine as it was is because it matched the
> original behavior better (and I was really only using a lazy prereq
> because we didn't have a non-lazy version). But there's really no reason
> _not_ to be lazy, so as long as it isn't breaking anything I think
> that's a better way forward. (And if it is breaking something, that
> something should be fixed).

I'm glad you agree!

Thanks, Dscho