Declare pkg-config dependencies

[osa1]

No description provided.

[vshabanov]

It fails Travis CI (for some reason Cabal 2.5 can't parse output of pkg-config --modversion) and not all systems have pkg-config so it's necessary to take it into account somehow.

Do you really need pkg-config? HsOpenSSL has a lot of options for various platforms and even tries autodetect OpenSSL installation path on macOS.

[osa1]

Thanks for the quick response.

I have no idea if I absolutely need this, but this was needed to make this package buildable on NixOS. Maybe @bgamari can provide more info on this as he suggested me adding this field.

[osa1]

Just confirmed with @phadej that the pkg-config --modversions parsing problem is a Cabal bug and it now fixed in haskell/cabal#163 .

It'll take some time for that change to be shipped though.

[vshabanov]

Great. It seems that following scheme is used in tests related to fix:

Flag use-pkg-config default: False manual: True ... Library ... if flag(use-pkg-config) pkgconfig-depends: ... else ... 

Perhaps it worth to adopt it so HsOpenSSL could be used on all systems with or without pkg-config

[vshabanov]

Closing this PR, since #51 was merged.