Re: testsuite: introduce hostedlib effective target

[Jonathan Wakely <jwakely@redhat.com>]

On Tue, 7 Nov 2023 at 10:04, Alexandre Oliva <oliva@adacore.com> wrote:
>
> [adding libstdc++@]
>
> On Nov  5, 2023, Mike Stump <mikestump@comcast.net> wrote:
>
> > Ick.
>
> Indeed ;-)
>
> > I wish there were fewer changed lines and not 1 per test
> > case. It feels like we've painted ourselves into a corner.
>
> The libstdc++ testsuite took a different approach, detecting missing
> headers (and libraries?) at error pruning time, and xfailing the tests,
> which seems to be more in line with what you are looking for.
>
> That approach, though more expedient, seems more fragile to me, in that
> an actual bug that caused headers to go missing would cause tests to be
> silently skipped rather than fail.

I don't think we XFAIL based on missing headers. We XFAIL based on a
specific #error message in certain headers.

If a header goes missing, we'll still XFAIL.

>
> I expect the set of headers, and thus of affected tests, won't by very
> dynamic, so it's kind of a one-shot change.
>
> Of course new tests might be added that rely on such headers, and would
> likely go unnoticed until someone tries them on a non-hosted libstdc++.

Since GCC 13 you don't need to build a non-hosted libstdc++ to test
it, you can just add -ffreestanding to the runtestflags.

> We could alleviate this if libstdc++ headers that are not installed on
> hosted systems issued a warning (conditional on some macro defined by
> the testsuite, say -D_GLIBCXX_WARN_HOSTED_ONLY).

That's exactly what happens (except #error not #warning) when you
compile with -ffreestanding.

>  For tests aimed
> exclusively at hosted libstdc++, we'd then use a dg directive that both
> implied this requirement, and changed the macro definition to suppress
> the warning.  Then anyone who added a testcase that included hosted
> headers without indicating its hostedlib requirement would get a fail
> even when testing with a hosted libstdc++.

I don't think we need to add checks for a new macro and then use that
when testing, you can just test with -ffreestanding instead. This
already works today.