lib/plugins: take ownership of modules utils

These util functions were previously defined in `modules`, but
`plugins.utils` is a better home.

lib/plugins/default.nix

@@ -3,6 +3,7 @@
   lib,
 }:
 {
+  utils = call ./utils.nix { };
   neovim = call ./neovim.nix { };
   vim = call ./vim.nix { };
 

lib/plugins/mk-neovim-plugin.nix

@@ -61,7 +61,7 @@ let
         })
       '';
 
-      luaConfigAtLocation = lib.nixvim.modules.mkConfigAt configLocation cfg.luaConfig.content;
+      luaConfigAtLocation = lib.nixvim.plugins.utils.mkConfigAt configLocation cfg.luaConfig.content;
     in
     {
       meta = {
@@ -139,7 +139,7 @@ let
 
               # Apply any additional configuration added to `extraConfig`
               (lib.optionalAttrs (args ? extraConfig) (
-                lib.nixvim.modules.applyExtraConfig {
+                lib.nixvim.plugins.utils.applyExtraConfig {
                   inherit extraConfig cfg opts;
                 }
               ))

lib/plugins/mk-vim-plugin.nix

@@ -116,7 +116,7 @@ let
             colorscheme = lib.mkDefault colorscheme;
           })
           (lib.optionalAttrs (args ? extraConfig) (
-            lib.nixvim.modules.applyExtraConfig {
+            lib.nixvim.plugins.utils.applyExtraConfig {
               inherit extraConfig cfg opts;
             }
           ))

lib/plugins/utils.nix

@@ -0,0 +1,34 @@
+{ lib }:
+{
+
+  /**
+    Apply an `extraConfig` definition, which should produce a `config` definition.
+    As used by `mkVimPlugin` and `mkNeovimPlugin`.
+
+    The result will be wrapped using a `mkIf` definition.
+  */
+  applyExtraConfig =
+    {
+      extraConfig,
+      cfg,
+      opts,
+      enabled ? cfg.enable or (throw "`enabled` argument not provided and no `cfg.enable` option found."),
+    }:
+    let
+      maybeApply = x: maybeFn: if builtins.isFunction maybeFn then maybeFn x else maybeFn;
+    in
+    lib.pipe extraConfig [
+      (maybeApply cfg)
+      (maybeApply opts)
+      (lib.mkIf enabled)
+    ];
+
+  mkConfigAt =
+    loc: def:
+    let
+      isOrder = loc._type or null == "order";
+      withOrder = if isOrder then lib.modules.mkOrder loc.priority else lib.id;
+      loc' = lib.toList (if isOrder then loc.content else loc);
+    in
+    lib.setAttrByPath loc' (withOrder def);
+}