Add Stack + Nix CI integration

[psibi]

This PR tests against latest three stackage resolvers covering different major ghc versions.

[cdepillabout]

review

[cdepillabout]

nitpick: I'm not very familiar with make, but generally when I see people using recursive make, they call it recursively like $(MAKE): https://www.gnu.org/software/make/manual/html_node/Recursion.html.

[psibi]

Thanks, I wasn't aware of that!

[cdepillabout]

review

[psibi]

After speaking to @cdepillabout , we decided that it's probably not a good idea to use Nix with a CI like that.

[jappeace]

Hi, I'm a bit confused, could you clarify on why it's not a good idea to use nix?
Can't we test against different versions of ghc with nix? I'm reasonably sure I've done that before (here for example)

Have a good weekend 🙂

[psibi]

@jappeace There were two reasons specified by @cdepillabout (correct me if I mis-understood something!):

• If the idea is to test against last three stackage lts resolvers, it's just much easier to test it using the usual approach of using stack. (similar to how it's done for the package fakedata)
• This package doesn't have any native dependency etc to actually make it useful to use Nix.

Also, if you can see the CI builds, the lts14 builds fail because of some weird issue going on with the way Nix packages ghc865Binary. So for this one case - we have to either go to an older nix package set to make it work or actually fix the nix issue.