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

[Johannes Schindelin <Johannes.Schindelin@gmx.de>]

Hi Peff,

On Thu, 26 Mar 2020, Jeff King wrote:

> On Wed, Mar 25, 2020 at 05:41:19AM +0000, Johannes Schindelin via GitGitGadget wrote:
>
> > In preparation for fixing that, let's move all of this code into lazy
> > prereqs.
>
> 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.

> > Side note: it was quite tempting to use a hack that is possible because
> > we do not validate what is passed to `test_lazy_prereq` (and it is
> > therefore possible to "break out" of the lazy_prereq subshell:
> >
> > 	test_lazy_prereq GPG '...) && GNUPGHOME=... && (...'
>
> No, it is not tempting at all to me to do something so gross. :)

Well, maybe it was not tempting to _you_, but to _me_, it was so tempting
that I had implemented and committed it before I made up my mind and
changed it again.

> > +test_lazy_prereq GPG '
> > +	gpg_version=$(gpg --version 2>&1)
>
> One thing I observed while doing my patch is that lazy_prereq blocks do
> not get run through the &&-chain linter. So this is OK, but I wonder if
> we should be future-proofing with braces. I don't care _too_ much either
> way, though.

I actually like that the prereq blocks are exempt from this && chain
linting, and would like to refrain from adding braces "just because".

> > +	test $? != 127 || exit 1
>
> I have a slight preference for "return 1" here. The "exit 1" works
> because test_lazy_prereq puts us in an implicit subshell. But I think
> this sets a bad example for people writing regular tests, where there is
> no such subshell (and "return 1" is the only correct way to do it).

There are two reasons why I did not use `return` here:

- To me, prereq code is very distinct from writing tests. Just like we do
  not &&-chain all the shell functions that live outside of tests, I don't
  want to &&-chain all the prereq code.

  The point of the tests' commands is not to fail. The point of prereq's
  code is to fail if the prereq is not met.

- 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.

> >  	case "$gpg_version" in
> > -	'gpg (GnuPG) 1.0.6'*)
> > +	"gpg (GnuPG) 1.0.6"*)
> >  		say "Your version of gpg (1.0.6) is too buggy for testing"
> > +		exit 1
>
> Ditto here.
>
> > @@ -25,55 +38,54 @@ then
> >  		# To export ownertrust:
> >  		#	gpg --homedir /tmp/gpghome --export-ownertrust \
> >  		#		> lib-gpg/ownertrust
> > -		mkdir ./gpghome &&
> > -		chmod 0700 ./gpghome &&
> > -		GNUPGHOME="$PWD/gpghome" &&
> > -		export GNUPGHOME &&
> > +		mkdir "$GNUPGHOME" &&
> > +		chmod 0700 "$GNUPGHOME" &&
>
> Compared to mine this keeps the mkdir in the prereq. That seems fine to
> me. Other prereqs do depend on the directory existing, but they all
> depend on GPG itself, so they'd be fine.

Yes. And conceptually, I like that the prereq is responsible for creating
that directory.

> > +test_lazy_prereq GPGSM '
> > +	test_have_prereq GPG &&
>
> 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.

Ciao,
Dscho