[llvm] db008af - [llvm] Repair the modules build with C++17

[David Blaikie via llvm-commits]

On Thu, Oct 6, 2022 at 10:03 AM Jonas Devlieghere <jonas at devlieghere.com> wrote:
>
> Hey Dave,
>
> Apologies for missing this e-mail. This somehow got caught in a mail filter and never made it to my inbox. I only saw the thread because someone else pinged me directly about it. Not sure if there's a way in Gmail to debug this after the fact, but I've made some changes to my mail rules that should prevent this in the future.

*fingers crossed* happy to help debug that if you like - but mostly
all I can probably offer is to send various test emails at points to
test your rules (presumably this email itself should qualify as such a
test... maybe?).

But, yeah, I should escalate reviews via discord/discourse/chat/etc
moreso than I do. Sometimes I just get a bit lazy about it.

> As far as the change is concerned, I agree that it's unfortunate that we need these workarounds. I suspect that it's a bug in the modules implementation, but I have no evidence to back that up and I'm not familiar enough with that part of clang to productively investigate that issue myself. I've filed a radar on the folks that maintain that part of clang.

Thanks! I'm glad there are some folks who might be able to take a look.

>  My motivation was limited to getting the LLDB bot building again after the C++17 migration broke it.

Yeah, I appreciate the desire to keep things working, but worry about
keeping things working that we aren't maintaining/don't know why they
work/don't work the way they do.

> We have (unfortunately) a bunch of workarounds in LLVM, often for quirks in other compilers and older standard libraries. I don't think this is any different except maybe that we have a little bit more agency here because it's clang itself. To answer your question/concern: like those other quirks, I wouldn't expect anyone to actively go out of their way to avoid this construct. Like those other quirks, I think it's totally fair to deal with those issues in a reactive matter, that is if we didn't fix the issue ourselves already, which Adrian (CC'd) has been silently doing for the majority of the modules issues.

Yeah, I've often tried to poke at Adrian when he's committed changes
like this too - and I do think part of the difference is that we
maintain these things. If you want to keep a modules buildbot working
it's presumably because you care about modules working - so these bugs
presumably are part of the interest in keeping the bot working?
Otherwise we could turn down the bot - I don't think many LLVM
developers are actually building with modules enabled, are they/is
that what the buildbot is there to support?

- Dave