Add devShell.mkShellArgs (#92)

CHANGELOG.md

@@ -6,6 +6,7 @@
   - #63: Add `config.haskellProjects.${name}.outputs` containing all flake outputs for that project.
   - #49 & #91: The `packages` option now autodiscovers the top-level `.cabal` file (in addition to looking inside sub-directories) as its default value.
   - #69: The default flake template creates `flake.nix` only, while the `#example` one creates the full Haskell project template.
+  - #92: Add `devShell.mkShellArgs` to pass custom arguments to `mkShell`
 - API changes
     - #37: Group `buildTools` (renamed to `tools`), `hlsCheck` and `hlintCheck` under the `devShell` submodule option; and allow disabling them all using `devShell.enable = false;` (useful if you want haskell-flake to produce just the package outputs).
     - #64: Remove hlintCheck (use [treefmt-nix](https://github.com/numtide/treefmt-nix#flake-parts) instead)

flake-module.nix

@@ -69,6 +69,21 @@ in
                   A [check](flake-parts.html#opt-perSystem.checks) to make sure that your IDE will work.
                 '';
               };
+              mkShellArgs = mkOption {
+                type = types.attrsOf types.raw;
+                description = ''
+                  Extra arguments to pass to `pkgs.mkShell`.
+                '';
+                default = { };
+                example = ''
+                  {
+                    shellHook = \'\'
+                      # Re-generate .cabal files so HLS will work (per hie.yaml)
+                      ''${pkgs.findutils}/bin/find -name package.yaml -exec hpack {} \;
+                    \'\';
+                  };
+                '';
+              };
             };
           };
           projectSubmodule = types.submoduleWith {

haskell-project.nix

@@ -74,14 +74,16 @@ in
           hlint;
       };
       nativeBuildInputs = lib.attrValues (defaultBuildTools finalPackages // config.devShell.tools finalPackages);
-      devShell = finalPackages.shellFor {
-        inherit nativeBuildInputs;
+      mkShellArgs = config.devShell.mkShellArgs // {
+        nativeBuildInputs = (config.devShell.mkShellArgs.nativeBuildInputs or [ ]) ++ nativeBuildInputs;
+      };
+      devShell = finalPackages.shellFor (mkShellArgs // {
         packages = p:
           map
             (name: p."${name}")
             (lib.attrNames config.packages);
         withHoogle = true;
-      };
+      });
     in
     {
       finalPackages = config.basePackages.extend config.finalOverlay;

test/flake.nix

@@ -46,9 +46,15 @@
             # docs.
             foo = self.callCabal2nix "foo" (inputs.haskell-multi-nix + /foo) { };
           };
-          devShell.tools = hp: {
-            # Adding a tool should make it available in devshell.
-            fzf = pkgs.fzf;
+          devShell = {
+            tools = hp: {
+              # Adding a tool should make it available in devshell.
+              fzf = pkgs.fzf;
+            };
+            mkShellArgs.shellHook = ''
+              echo "Hello from devshell!"
+              export FOO=bar
+            '';
           };
         };
         # haskell-flake doesn't set the default package, but you can do it here.

test/test.sh

@@ -16,3 +16,11 @@ which ghcid && exit 2 || echo
 
 # Adding a buildTool (fzf, here) should put it in devshell.
 which fzf
+
+# mkShellArgs works
+if [[ "$FOO" == "bar" ]]; then 
+    echo "$FOO"
+else 
+    echo "FOO is not bar" 
+    exit 2
+fi