Partially revert Nixpkgs based prebuilt dependencies import

[mboes]

#442 moved us to having external dependencies for all Cabal packages, including base, generated by Nixpkgs based machinery. This is getting in the way of our Windows port. As we make progress through our test suite, supporting increasingly more things, we'll find ourselves reverting each test one by one to the haskell_import style that preceded #442.

It's best to roll back parts of #442 in a sytematic way. I'm not suggesting here to remove all of it (not yet at any rate). But to designate the following packages, which ship with GHC, as haskell_import only. These are the packages that are needed for nearly all tests of core functionality. The other packages are only needed for protobuf toolchains and the like. Windows support for that is not a priority.

Any references to the following packages (and only these) should be converted to haskell_import-style:

• base
• binary
• bytestring
• containers
• directory
• filepath
• template-haskell
• ghc-prim
• text

Aka "@hackage//:base" becomes ":base" with a haskell_import(name = "base") target added somewhere in the same BUILD file.

[thufschmitt]

You could make this transition a bit more automated by having a toplevel hackage/BUILD file with

[
  haskell_import(name = name)
  for name in ["base", "binary", … ]
]

And bulk-replace references to @hackage//:base to //hackage:base (or @io_tweag_rules_haskell//hackage:base)

[nmattia]

Yup, that's what I went for (somewhat): https://github.com/tweag/rules_haskell/compare/nm-pkg-boot

now dealing with visibility issues

[mboes]

I don't think this warrants a new public API function that we'll have to support for users just yet. We have haskell_import, and we're using it in rules_haskell-internal tests (and tests only). So let's keep changes contained to that. Which is easy to do with one single variant to @regnat's idea: move these labels to anywhere under //tests/....

[nmattia]

Using @regnat 's approach: https://github.com/tweag/rules_haskell/compare/nm-pkg-boot-2

Much simpler, thanks!