docs: use mdBook for NixOS options

This is part of #250

Co-authored-by: Shahar "Dawn" Or <mightyiampresence@gmail.com>

Author: jfly

flake.nix

@@ -35,7 +35,7 @@
           ./modules/formatting.nix
           ./modules/integration-tests
           ./modules/nci.nix
-          ./modules/nixos-manual
+          ./modules/nixos-manual.nix
           ./modules/nixos-modules-lib.nix
           ./modules/private-nixos-modules
           ./modules/program-docs.nix

modules/nixos-manual.nix

@@ -0,0 +1,70 @@
+{
+  lib,
+  self,
+  ...
+}:
+{
+  perSystem =
+    {
+      self',
+      system,
+      pkgs,
+      ...
+    }:
+    let
+      filterOptions = import ../filterOptions.nix lib;
+
+      configuration = lib.nixosSystem {
+        modules = [
+          self.nixosModules.api
+          self.nixosModules.fetcher
+          {
+            nixpkgs.hostPlatform = system;
+          }
+        ];
+      };
+
+      options = filterOptions (
+        path: option: lib.any (lib.hasPrefix "${self}/") option.declarations
+      ) configuration.options;
+
+      optionsDocs = pkgs.buildPackages.nixosOptionsDoc {
+        inherit options;
+        variablelistId = "options";
+        transformOptions = options: builtins.removeAttrs options [ "declarations" ];
+      };
+
+      optionsMd =
+        pkgs.runCommand "pr-tracker-nixos-options-html" { nativeBuildInputs = [ pkgs.nixos-render-docs ]; }
+          ''
+            nixos-render-docs options commonmark \
+              --manpage-urls <(echo "{}") \
+              --revision provide-because-required-but-seems-to-be-unused \
+              ${optionsDocs.optionsJSON}/share/doc/nixos/options.json $out
+          '';
+
+      summaryMd = pkgs.writeTextFile {
+        name = "SUMMARY.md";
+        text =
+          # markdown
+          ''
+            [Options](options.md)
+          '';
+      };
+    in
+    {
+      packages.nixos-manual =
+        pkgs.runCommand "pr-tracker-nixos-manual"
+          {
+            nativeBuildInputs = [ pkgs.mdbook ];
+          }
+          ''
+            mkdir src
+            ln -s ${summaryMd} src/SUMMARY.md
+            ln -s ${optionsMd} src/options.md
+            mdbook build --dest-dir $out
+          '';
+
+      checks."packages/nixos-modules-manual" = self'.packages.nixos-manual;
+    };
+}