Allow Nix-based consumers to avoid the default bindist GHC fetch

[jonathanlking]

MODULE.bazel registers a bindist-based GHC toolchain as a (non-dev) dependency:

haskell_toolchains = use_extension(
    "@rules_haskell//extensions:haskell_toolchains.bzl",
    "haskell_toolchains",
)
haskell_toolchains.bindists()

# ...

register_toolchains(
    "@all_bindist_toolchains//:all",
    "@rules_haskell_ghc_windows_amd64_cc_toolchain//:all",
    "@rules_haskell_python_local//:toolchain",
)

While this provides a convenient zero-configuration default, for those provisioning GHC via Nix (using rules_haskell_nix) this causes issues.
The bindist extension eagerly fetches a platform-native GHC binary distribution at repository-fetch time, which expects host system libraries (e.g. libtinfo.so.5) that aren't present on Nix-based systems. This fetch fails even though the consumer never asked for a bindist.

There doesn't appear to be a way for a consumer to opt out of the propagating bindist? Our current workaround is to patch both declarations with dev_dependency = True:

This is consistent with the Nix toolchain register_toolchains, which already has dev_dependency = True, but it does mean that consumers who want the default bindist would need to explicitly request it in their own MODULE.bazel.

[avdv]

Can you try to depend on rules_haskell_nix before rules_haskell ? That way it should register the nix based toolchain before the bindist one.

I'm on NixOS and I don't have a problem with the bindist toolchain in my project.