Buildbot now fails to build wine dependencies

[Clemens Lang]

Hey,

On Tue, Jul 04, 2017 at 10:00:16PM +0200, Clemens Lang wrote:
> > I am attaching a patch to only print active variants that are not
> > enabled by default (or disabled default variants). To me the result
> > looks like what we want to have:
> > 
> > $ tools/dependencies.tcl wine | grep -E 'glib2|cairo'
> > glib2 +universal
> > cairo +universal
> > $ tools/dependencies.tcl gtk3 +quartz | grep -E 'glib2|cairo'
> > glib2 +quartz
> > cairo
> 
> No, this won't work, because with this output you can no longer
> distinguish 'cairo (default variants)' from 'cairo -quartz-x11'. This
> is probably not a valid configuration for the cairo port specifically,
> but you get the idea.

I had another look at your proposed patch. In general, the idea of
printing active variants that are not enabled by default and disabled
default variants is correct. We need a string that uniquely identifies a
specific variant combination when passed to 'port install', and your
idea fulfills that property.

However, the implementation has problems:

- Due to the way how $depinfo(active_variants) works, it only contains
  positive variants. Hence $active_variants($variant) eq "-" can never
  be true and your code will never disable a default variant. This works
  in your gtk3 +quartz example for the same reason that 'port info glib2
  +quartz' does not show x11 as a default variant.
- $default_variants does not contain default variants that have been
  disabled for this port. Just because a variant is not in
  default_variants does not mean that it is not a default variant of the
  given port, it might just have been disabled for this instance. It's
  weird, I know.

Note, btw, that this did work correctly before
  https://github.com/macports/mpbb/commit/4462924d822cb61464b6ecb8badcc9949231527b
I'm adding Joshua to Cc.

Since Joshua's commit did improve speed quite a bit (turns out the extra
Portfile execution comes with a hefty performance penalty), how about
this approach:

 - Print all selected variants that are not default.
 - Intersect the set of variants explicitly disabled on the command line
   with the set of available variants of a port, and print those.

This will still give us a situation where disabling a non-default
variant of a port will cause a failcache miss, but your patch already
had these downsides.

Reviews please: https://github.com/macports/mpbb/pull/4

-- 
Clemens