readme.md

This gist demonstrates a ghcide setup with nix.

No project file (.cabal, package.yaml, stack.yaml, etc.) is necessary.

Before attempting editor integration, test ghcide in the terminal by running this command:

nix-shell --pure --run ghcide

This will search for Haskell source files and print any errors encountered, which can help you determine whether e.g. ghcide is seeing all of your project dependencies correctly.

For Visual Studio Code integration, install the ghcide extension and use the following settings:

• Executable path: ./ghcide.sh
• Arguments: (empty)

ghcide.sh

#! /usr/bin/env bash

set -eufo pipefail

nix-shell --pure --run 'ghcide --lsp'

hie.yaml

cradle:
  direct:
    arguments:
      - -no-user-package-db

shell.nix

let
  pkgs = import <nixpkgs> {};

  ghcVersion = "ghc865";

  haskellPackages = pkgs.haskell.packages.${ghcVersion}.override { 
    overrides = self: super: {
      # If you need a particular version of a package instead
      # of the default that nixpkgs provides, specify it here.
    };
  };
  
  haskell = haskellPackages.ghcWithPackages (p: map (name: p.${name}) [
     "aeson"
     "async"
     "bytestring"
     # etc., the rest of the Hackage packages you use
  ]);
  
  ghcide =
    let 
      url = "https://github.com/hercules-ci/ghcide-nix/tarball/master";
    in
      (import (builtins.fetchTarball url) {})."ghcide-${ghcVersion}";

in
  pkgs.mkShell {
    buildInputs = [
      haskell
      haskellPackages.ghcid
      ghcide
    ];
    LC_ALL = "en_US.UTF-8";
    LOCALE_ARCHIVE = "${pkgs.glibcLocales}/lib/locale/locale-archive";
    shellHook = ''
      export NIX_GHC="${haskell}/bin/ghc"
      export NIX_GHCPKG="${haskell}/bin/ghc-pkg"
      export NIX_GHC_DOCDIR="${haskell}/share/doc/ghc/html"
      export NIX_GHC_LIBDIR=$( $NIX_GHC --print-libdir )
    '';
  }

what is the purpose of hie.yml? I was able to get this working without it, but wondering if I missed something?

also the LOCAL_ARCHIVE was consistently causing this to fail for me so I removed it. Is there a reason that it's necessary? The error was:

error: cannot coerce null to a string, at /Users/willisplummer/code/nix-haskell-starter/shell.nix:29:19

@willisplummer I don't remember the purpose of hie.yml and I no longer use it, so I suspect you can safely ignore it!

I typically set LC_ALL and LOCALE_ARCHIVE in any shell hook because when nix-shell strips environment variables, it unsets the locale and causes encoding issues, and setting these tends to get everything reliably back into UTF-8. I'm not sure why it wouldn't be working for you.