Update hwloc; don't require libpciaccess on OS X

[eschnett]

• hwloc 1.11.2 is available.
• libpciaccess is not supported on OS X; don't require it there.

[alalazo]

I was wondering why not a variant for libpciaccess. My concern is that this approach will force every user to name the architecture linux if they want to activate the dependency.

[eschnett]

libpciaccess should be the default, except on OS X. Is this possible with variants?

[tgamblin]

It's not at the moment. You can do this:

    variant('libpciaccess', default=True, 'Enable PCI access library')
    depends_on('libpciaccess', when='+libpciaccess')

But then OS X users will need to know to build with -libpciaccess, which isn't ideal. I would say to add the variant for now, possibly keeping the hard-coded setting in your own branch, and we could work on a way to add predicates instead of just True/False for the value of default.

[alalazo]

I don't think it can be automated completely ( @tgamblin correct me if I am wrong ). Something like:

variant('libpciaccess', default=True, description='Activates dependency on libpciaccess')
...
depends_on('libpciaccess', when='+libpciaccess')

would require to explicitly type:

spack install hwloc~libpciaccess

on OS X.

[eschnett]

If it's so complicated to not use a particular package on certain systems, then I think it might be easier to change libpciaccess to skip the configure/make/install steps on OS X, leaving Spack to think that this package actually exists.

[tgamblin]

Let me see what i can add -- one reason this is complicated is that the spec syntax doesn't really have a way to say "not" for architectures right now -- Specs are really match objects and they only match in the positive.

A simple way to do this would be something like:

depends_on('libpciaccess', when='!=darwin-x86_64')

that would be much clearer than the above proposals. I would need to think through how the spec syntax should be modified to support this, but it is something we need.

The other option would be to just add "when_not", which might be easier short-term. That would look like this:

depends_on('libpciaccess', when_not='=darwin-x86_64')

You could test either of these in install by just writing:

    if 'libpciaccess' in spec:
        ...

Would either of those work for you?

[eschnett]

Either of these dependency specification would work fine.

[eschnett]

I've modified the patch:

• Installing libpciaccess now works on OS X, by not actually doing anything (since it doesn't support OS X)
• hwloc is left unmodified

[tgamblin]

This seems reasonable for now -- thanks for updating! I can try to work in my proposed better solution (just don't depend on pciaccess on OS X) soon.