Added documentation about modules.

NixOS and Home Manager both automatically generate documentation using 'nixosOptionsDoc', and now so does hylonix.

I can't find any standard reference for where this documentation should go, so I have created a doc attribute in the flake.

.gitignore

@@ -3,5 +3,6 @@
 !.gitignore
 !flake.nix
 !flake.lock
+!docs/**/*.nix
 !lib/**.nix
 !modules/**/*.nix

docs/default.nix

@@ -0,0 +1,56 @@
+{
+  pkgs,
+  lib,
+  self,
+  ...
+}:
+
+let
+  baseModule = _: {
+    # Hide documentation relating to _module.args, which isn't a part
+    # of this flake
+    options._module.args = lib.mkOption { internal = true; };
+    # Turn off the checks on the config. We only want the options, so
+    # don't eval the config.
+    config._module.check = false;
+  };
+
+  makeModuleDocs =
+    subcomponent: modules:
+    let
+      eval = lib.evalModules {
+        modules = [ baseModule ] ++ modules;
+        class = "hylonix";
+        specialArgs = { inherit pkgs lib; };
+      };
+      docs = pkgs.buildPackages.nixosOptionsDoc {
+        inherit (eval) options;
+        warningsAreErrors = false;
+      };
+    in
+    {
+      # These formats are generated by nixosOptionsDoc,
+      # so may as well expose them.
+      asciiDoc = docs.optionsAsciiDoc;
+      commonMark = docs.optionsCommonMark;
+      json = docs.optionsJSON;
+      nix = docs.optionsNix;
+    };
+in
+{
+  modules = {
+    all = makeModuleDocs "modules" (
+      builtins.attrValues self.hmModules ++ builtins.attrValues self.nixosModules
+    );
+
+    hm = {
+      all = makeModuleDocs "hmModules" (builtins.attrValues self.hmModules);
+      module = builtins.mapAttrs (k: v: makeModuleDocs "hmModules-${k}" [ v ]) self.hmModules;
+    };
+
+    nixos = {
+      all = makeModuleDocs "nixosModules" (builtins.attrValues self.nixosModules);
+      module = builtins.mapAttrs (k: v: makeModuleDocs "nixosModules-${k}" [ v ]) self.nixosModules;
+    };
+  };
+}

flake.nix

@@ -11,6 +11,8 @@
       forAllSystems = nixos.lib.genAttrs nixos.lib.systems.flakeExposed;
     in
     {
+      docs = forAllSystems (system: nixos.legacyPackages.${system}.callPackage ./docs { inherit self; });
+
       formatter = forAllSystems (system: nixos.legacyPackages.${system}.nixfmt-tree);
 
       hmModules = import ./modules/home-manager self.lib.hylonix;