modules: add fn module to define functions

lib/types.nix

@@ -43,7 +43,7 @@ let
         '';
       };
       buffer = mkOption {
-        type = with types; nullOr str;
+        type = with types; nullOr attrs;
         default = null;
         description = ''
           The mapping will be effective in the current buffer only.

module-list.nix

@@ -9,6 +9,7 @@
   ./modules/filetype.nix
   ./modules/input.nix
   ./modules/plugin.nix
+  ./modules/fn.nix
 
   ./modules/plugins/theme/catppuccin.nix
   ./modules/plugins/style/neoformat.nix

modules/fn.nix

@@ -0,0 +1,59 @@
+{ lib, ... }:
+
+let
+
+  fnOpts = { name, config, ... }: {
+    options = with lib; {
+      args = mkOption {
+        type = with types; listOf str;
+        default = [ ];
+      };
+      content = mkOption {
+        type = with types; nullOr attrs;
+        default = null;
+      };
+      settings = mkOption {
+        type = types.functionTo (lib.types.submoduleWith {
+          modules = [
+            ./vim/keymap.nix
+            # ./vim/opts.nix
+          ];
+          specialArgs = { inherit lib; };
+        });
+        default = { };
+      };
+
+      lambda = mkOption {
+        type = types.attrs;
+        readOnly = true;
+        internal = true;
+      };
+    };
+
+    config = {
+      lambda = with lib.nix2lua;
+        let
+          fnArgs = builtins.listToAttrs (map (v: { name = v; value = raw v; }) config.args);
+          innerCfg = config.settings fnArgs;
+        in
+        lambda config.args (lib.flatten [
+          config.content
+
+          (lib.flip map innerCfg.vim.keymap.set ({ mode, lhs, rhs, ... } @ vars:
+            let
+              buf = lib.optionalString (vars.buffer != null) vars.buffer.raw;
+              m = if builtins.isList mode then lib.head mode else mode;
+            in
+            if innerCfg.vim.keymap._validate."${buf}"."${m}"."${lhs}" == rhs then vars.genConfig
+            else abort "This case should never happen."
+          ))
+        ]);
+    };
+  };
+in
+{
+  options.fn = with lib; mkOption {
+    type = with types; attrsOf (submodule fnOpts);
+    default = { };
+  };
+}

modules/vim/keymap.nix

@@ -30,7 +30,7 @@ let cfg = config.vim.keymap; in
               else m
             )));
 
-            buf = lib.optionalString (buffer != null) buffer;
+            buf = lib.optionalString (buffer != null) buffer.raw;
           in
           lib.foldl lib.recursiveUpdate { }
             (lib.flip map unwrappedModes (m: {