Add cross compilers to haskell.nix flake devShell

[facundominguez]

I'm trying to get a shell with a cross-compiler and having some difficulties.

The documentation on cross-compilation says how to build a project with either stack or cabal. I'm aiming to build with bazel, though, and I'm only interested in getting the build tools.

I found my way to get a native compiler in a shell for a dummy cabal project. However, haskell.nix has resisted all my attempts to get the shell with a cross-compiler for aarch64. My nix code is not very succinct either, which prods me to ask for an example from a more knowledgeable person.

Thanks in advance.

[hamishmack]

Do the same a you would for a non cross compiling shell, but instead of using haskell-nix use pkgsCross.aarch64-multiplatform.haskell-nix. For instance to get a shell to cross compile the hello package from hackage:

$ cat shell.nix 
{ haskellNix ? import (builtins.fetchTarball "https://github.com/input-output-hk/haskell.nix/archive/master.tar.gz") {}
, pkgs ? import haskellNix.sources.nixpkgs haskellNix.nixpkgsArgs
}: (pkgs.pkgsCross.aarch64-multiplatform.haskell-nix.hackage-project {name = "hello"; version = "1.0.0.2"; compiler-nix-name = "ghc8102"; }).hsPkgs.shellFor {}

$ nix-shell
trace: Using latest index state for hello!
trace: Using index-state: 2020-10-12T00:00:00Z for hello
trace: Shell for hello
trace: Shell for hello

$ aarch64-unknown-linux-gnu-ghc --version
The Glorious Glasgow Haskell Compilation System, version 8.10.2

[facundominguez]

Thanks @hamishmack! That quite fits the bill.

[facundominguez]

I'm trying to build with TH and this shell is missing the iserv-proxy and remote-iserv that would be necessary. I'll share here if I can figure out how to get those.

[facundominguez]

Here's my best attempt so far:

let crossPkgs = pkgs.pkgsCross.aarch64-multiplatform;
    haskellNix = import (builtins.fetchTarball https://github.com/input-output-hk/haskell.nix/archive/b406bb1d5bed581f651ae18a5d3ed07f47ace2b9.tar.gz) {};
    pkgs = import haskellNix.sources.nixpkgs haskellNix.nixpkgsArgs;
in
pkgs.mkShell {
  buildInputs = 
    [ pkgs.buildPackages.ghc-extra-packages.ghc8102.iserv-proxy.components.exes.iserv-proxy
      crossPkgs.ghc-extra-packages.ghc8102.remote-iserv.components.exes.remote-iserv
      crossPkgs.buildPackages.haskell-nix.compiler.ghc8102
      pkgs.buildPackages.qemu
    ];
} 

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[hamishmack]

We recently added basic ghc devShells so we could use them in GitHub actions to test building projects without haskell.nix.

haskell.nix/flake.nix

Lines 147 to 154 in a306656

	} // __mapAttrs (compiler-nix-name: compiler:
	mkShell {
	buildInputs = [
	compiler
	haskell-nix.cabal-install.${compiler-nix-name}
	];
	}
	) (

It would be really nice to add cross compilation including aarch64 to those.

@facundominguez did the above code work in the end? Did you have to tell ghc where to look for iserv or did it find? If not then I suspect we might need some of the code from https://github.com/input-output-hk/haskell.nix/blob/master/overlays/linux-cross.nix

[facundominguez]

@facundominguez did the above code work in the end?

It worked well enough. Instead of using remote-iserv we moved to using ghc-iserv directly.
Here is the exact configuration.