inaki authored Mar 05, 2016 and Mikhail Glushenkov committed Apr 23, 2016

When solving, we now discard plans that would involve packages with a
pkgconfig-depends constraint which is not satisfiable with the current
set of installed packages (as listed by pkg-config --list-all).

This fixes https://github.com/haskell/cabal/issues/3016.

It is possible (in principle, although it should be basically impossible
in practice) that "pkg-config --modversion pkg1 pkg2... pkgN" fails to
execute for various reasons, in particular because N is too large, so
the command line becomes too long for the operating system limits.

If this happens, revert to the previous behavior of accepting any
install plan, regardless of any pkgconfig-depends constraints.

(cherry picked from commit c72aa8db)

+

Monitor the pkg-config db for changes

We use the pkg-config db as an input for the solver, so we ought to
monitor it for changes. The pkg-config tool makes this possible, if not
totally trivial.

(cherry picked from commit f968b41e)