docs/lib: generalise menu impl using module system

Move the mdbook menu rendering code into the module system and
generalise it to apply to multiple "categories" (mdbook parts) and
"types" of category (prefix, suffix, etc).

docs/lib/default.nix

@@ -10,19 +10,14 @@
 }:
 
 let
-  pageConfiguration = lib.evalModules {
+  menuConfiguration = lib.evalModules {
     modules = [
       pageSpecs
-      {
-        freeformType = lib.types.attrsOf (
-          lib.types.submoduleWith {
-            modules = [ ../modules/page.nix ];
-          }
-        );
-      }
+      ../modules/menu.nix
     ];
   };
-  pages = pageConfiguration.config;
+  cfg = menuConfiguration.config;
+  pages = cfg.functions;
 
   # Collect all page nodes into a list of page entries
   collectPages =
@@ -33,7 +28,7 @@ let
         children = builtins.removeAttrs node [ "_page" ];
       in
       lib.optional (node ? _page) node._page ++ lib.optionals (children != { }) (collectPages children)
-    ) (builtins.attrValues pages);
+    ) (builtins.attrValues (builtins.removeAttrs pages [ "_category" ]));
 
   # Normalised page specs
   pageList = collectPages pages;
@@ -60,11 +55,9 @@ let
           }
         );
 
-        passthru.config = pageConfiguration;
+        passthru.config = menuConfiguration;
 
-        passthru.menu = import ./menu.nix {
-          inherit lib pages;
-        };
+        passthru.menu = cfg._menu.text;
 
         passthru.pages = map (page: "${result}/${page.target}") pagesToRender;
       }

docs/lib/menu.nix

@@ -1,31 +0,0 @@
-{
-  lib,
-  pages,
-  indentSize ? "  ",
-}:
-let
-  pageToLines =
-    indent: parent: node:
-    let
-
-      children = lib.pipe node [
-        (lib.flip builtins.removeAttrs [ "_page" ])
-        builtins.attrValues
-      ];
-      # Only add node to the menu if it has content or multiple children
-      useNodeInMenu = node._page.target != "" || node._page.children > 1;
-      nextParent = if useNodeInMenu then node else parent;
-      nextIndent = if useNodeInMenu then indent + indentSize else indent;
-      loc = lib.lists.removePrefix (parent._page.loc or [ ]) node._page.loc;
-      menuName = lib.attrsets.showAttrPath loc;
-    in
-    lib.optional useNodeInMenu "${indent}- [${menuName}](${node._page.target})"
-    ++ lib.optionals (children != [ ]) (
-      builtins.concatMap (pageToLines nextIndent nextParent) children
-    );
-in
-lib.pipe pages [
-  builtins.attrValues
-  (builtins.concatMap (pageToLines "" null))
-  lib.concatLines
-]

docs/lib/pages.nix

@@ -4,19 +4,23 @@
 # If there is an issue parsing the file, the resulting markdown will not contain any function docs.
 
 {
-  lib.nixvim = {
-    _page = {
-      title = "lib.nixvim: Nixvim's functions";
-      source = ./index.md;
-    };
+  functions = {
+    _category.name = "Functions";
 
-    utils._page = {
-      title = "lib.nixvim.utils: utility functions";
-      functions.file = ../../lib/utils.nix;
-    };
-    lua._page = {
-      title = "lib.nixvim.lua: lua functions";
-      functions.file = ../../lib/to-lua.nix;
+    lib.nixvim = {
+      _page = {
+        title = "lib.nixvim: Nixvim's functions";
+        source = ./index.md;
+      };
+
+      utils._page = {
+        title = "lib.nixvim.utils: utility functions";
+        functions.file = ../../lib/utils.nix;
+      };
+      lua._page = {
+        title = "lib.nixvim.lua: lua functions";
+        functions.file = ../../lib/to-lua.nix;
+      };
     };
   };
 }