Add haskellFlakeProjectModules option (#79)

CHANGELOG.md

@@ -11,6 +11,7 @@
     - #64: Remove hlintCheck (use [treefmt-nix](https://github.com/numtide/treefmt-nix#flake-parts) instead)
     - #52: Expose the final package set as `finalPackages`. Rename `haskellPackages`, accordingly, to `basePackages`. Overlays are applied on top of `basePackage` -- using `source-overrides`, `overrides`, `packages` in that order -- to produce `finalPackages`.
     - #68: You can now use `imports` inside of `haskellProjects.<name>` to modularize your Haskell project configuration.
+      - #79: `flake.haskellFlakeProjectModules.<name>` option can be used to set and expose your Haskell project modules to other flakes.
       - #67: `overrides` will be combined using `composeManyExtensions`, however their order is arbitrary. This is an experimental feature, and a warning will be logged.
 
 ## 0.1.0

flake-module.nix

@@ -239,9 +239,20 @@ in
           };
         in
         {
-          options.haskellProjects = mkOption {
-            description = "Haskell projects";
-            type = types.attrsOf projectSubmodule;
+          options = {
+            haskellProjects = mkOption {
+              description = "Haskell projects";
+              type = types.attrsOf projectSubmodule;
+            };
+
+            haskellFlakeProjectModules = mkOption {
+              type = types.lazyAttrsOf types.deferredModule;
+              default = { };
+              description = ''
+                An attrset of `haskellProjects.<name>` modules that can be imported in
+                other flakes.
+              '';
+            };
           };
 
           config =

test/flake.nix

@@ -22,29 +22,26 @@
         inputs.haskell-flake.flakeModule
         inputs.check-flake.flakeModule
       ];
+      flake.haskellFlakeProjectModules.default = { pkgs, ... }: {
+        overrides = self: super: {
+          # This is purposefully incorrect (pointing to ./.) because we
+          # expect it to be overriden in perSystem below.
+          foo = self.callCabal2nix "foo" ./. { };
+        };
+        devShell = {
+          tools = hp: {
+            # Setting to null should remove this tool from defaults.
+            ghcid = null;
+          };
+          hlsCheck.enable = true;
+        };
+      };
       perSystem = { self', pkgs, ... }: {
         haskellProjects.default = {
           # Multiple modules should be merged correctly.
-          imports =
-            let
-              defaults = {
-                overrides = self: super: {
-                  # This is purposefully incorrect (pointing to ./.) because we
-                  # expect it to be overriden below.
-                  foo = self.callCabal2nix "foo" ./. { };
-                };
-                devShell = {
-                  tools = hp: {
-                    # Setting to null should remove this tool from defaults.
-                    ghcid = null;
-                  };
-                  hlsCheck.enable = true;
-                };
-              };
-            in
-            [ defaults ];
+          imports = [ self.haskellFlakeProjectModules.default ];
           overrides = self: super: {
-            # This overrides the overlay above (in `defaults`), because the
+            # This overrides the overlay above (in `flake.*`), because the
             # module system merges them in such order. cf. the WARNING in option
             # docs.
             foo = self.callCabal2nix "foo" (inputs.haskell-multi-nix + /foo) { };