modules/keymap: add validation

modules/vim/keymap.nix

@@ -1,10 +1,42 @@
-{ lib, ... }:
+{ config, lib, ... }:
 
+let cfg = config.vim.keymap; in
 {
   options.vim.keymap = with lib; {
+    _validate = mkOption {
+      #                  buffer   mode     lhs      rhs
+      type = with types; attrsOf (attrsOf (attrsOf (either str attrs)));
+      visible = false;
+      internal = true;
+      readOnly = true;
+    };
     set = mkOption {
       type = with types; listOf keymap;
       default = [ ];
     };
   };
+
+  config = {
+    vim.keymap._validate = lib.mkMerge
+      (map
+        ({ mode, lhs, rhs, buffer, ... }:
+          let
+            sourceModes = if builtins.isList mode then mode else [ mode ];
+            unwrappedModes = lib.flatten (lib.flip map sourceModes (m:
+              if m == "" then [ "n" "x" "s" "o" ]
+              else if m == "!" then [ "i" "c" ]
+              else if m == "v" then [ "x" "s" ]
+              else if m == "l" then [ "i" "c" "l" ]
+              else m
+            ));
+
+            buf = if buffer == null then "" else buffer;
+          in
+          lib.foldl lib.recursiveUpdate { }
+            (lib.flip map unwrappedModes (m: {
+              "${buf}"."${m}"."${lhs}" = rhs;
+            }))
+        )
+        cfg.set);
+  };
 }