modules/nixpkgs: initial pkgs option, drop defaultPkgs specialArg

This minimal implementation allows `nixpkgs.pkgs` to be defined, but
does not implement evaluating an instance from a pkgsPath when _not_
defined.

The `defaultPkgs` specialArg is dropped in favour of `nixpkgs.pkgs`
being defined. If it's not defined, an assertion is thrown.

In the future, a nixpkgs source path can be supplied, defaulting to the
flake's `inputs.nixpkgs`. Along with other `nixpkgs.*` options, this
will allow a `pkgs` instance to be evaluated within the module eval.

wrappers/_shared.nix

@@ -55,6 +55,10 @@ in
       _module.args.nixvimLib = lib.mkDefault config.lib.nixvim.extendedLib;
     }
 
+    # Use global packages by default in nixvim's submodule
+    # TODO: `useGlobalPackages` option and/or deprecate using host packages?
+    { programs.nixvim.nixpkgs.pkgs = lib.mkDefault pkgs; }
+
     # Propagate nixvim's assertions to the host modules
     (lib.mkIf cfg.enable { inherit (cfg) warnings assertions; })
 

wrappers/darwin.nix

@@ -18,7 +18,6 @@ let
   cfg = config.programs.nixvim;
   nixvimConfig = config.lib.nixvim.modules.evalNixvim {
     extraSpecialArgs = {
-      defaultPkgs = pkgs;
       darwinConfig = config;
     };
     modules = [

wrappers/hm.nix

@@ -17,7 +17,6 @@ let
   cfg = config.programs.nixvim;
   nixvimConfig = config.lib.nixvim.modules.evalNixvim {
     extraSpecialArgs = {
-      defaultPkgs = pkgs;
       hmConfig = config;
     };
     modules = [

wrappers/nixos.nix

@@ -18,7 +18,6 @@ let
   cfg = config.programs.nixvim;
   nixvimConfig = config.lib.nixvim.modules.evalNixvim {
     extraSpecialArgs = {
-      defaultPkgs = pkgs;
       nixosConfig = config;
     };
     modules = [

wrappers/standalone.nix

@@ -1,5 +1,6 @@
 default_pkgs: self:
 {
+  # TODO: Deprecate this arg in favour of using module options
   pkgs ? default_pkgs,
   lib ? pkgs.lib,
   extraSpecialArgs ? { },
@@ -18,10 +19,13 @@ let
       nixvimConfig = evalNixvim {
         modules = [
           mod
+          # TODO: only include this when `args?pkgs`:
+          {
+            _file = ./standalone.nix;
+            nixpkgs.pkgs = lib.mkDefault pkgs;
+          }
         ];
-        extraSpecialArgs = {
-          defaultPkgs = pkgs;
-        } // extraSpecialArgs;
+        inherit extraSpecialArgs;
       };
       inherit (nixvimConfig.config) enableMan build;
     in