lib/modules: pass inputs.nixpkgs into evalNixvim

Expose our locked nixpkgs as the `nixpkgs.source` module options.

This only happens when `evalNixvim` is part of a lib that was provided
`flake` as an argument.

Stubbed the `nixpkgs.source` option for now. Eventually, this will be
used to construct `pkgs` internally. For now, it's purely informational.

wrappers/_shared.nix

@@ -1,4 +1,6 @@
 {
+  # The nixvim flake
+  self,
   # Extra args for the `evalNixvim` call that produces the type for `programs.nixvim`
   evalArgs ? { },
   # Option path where extraFiles should go
@@ -57,7 +59,13 @@ in
   config = mkMerge [
     {
       # Make our lib available to the host modules
-      lib.nixvim = lib.mkDefault (import ../lib { inherit lib; });
+      # NOTE: user-facing so we must include the legacy `pkgs` argument
+      lib.nixvim = lib.mkDefault (
+        import ../lib {
+          inherit lib;
+          flake = self;
+        }
+      );
 
       # Make nixvim's "extended" lib available to the host's module args
       _module.args.nixvimLib = lib.mkDefault config.lib.nixvim.extendedLib;

wrappers/darwin.nix

@@ -22,7 +22,7 @@ in
 {
   _file = ./darwin.nix;
 
-  imports = [ (import ./_shared.nix { inherit evalArgs; }) ];
+  imports = [ (import ./_shared.nix { inherit self evalArgs; }) ];
 
   config = mkIf cfg.enable {
     environment.systemPackages = [

wrappers/hm.nix

@@ -24,7 +24,7 @@ in
 
   imports = [
     (import ./_shared.nix {
-      inherit evalArgs;
+      inherit self evalArgs;
       filesOpt = [
         "xdg"
         "configFile"

wrappers/nixos.nix

@@ -24,7 +24,7 @@ in
 
   imports = [
     (import ./_shared.nix {
-      inherit evalArgs;
+      inherit self evalArgs;
       filesOpt = [
         "environment"
         "etc"

wrappers/standalone.nix

@@ -9,7 +9,11 @@ default_pkgs: self:
 }:
 let
   # NOTE: we are importing this just for evalNixvim
-  helpers = import ../lib { inherit lib _nixvimTests; };
+  helpers = import ../lib {
+    inherit lib _nixvimTests;
+    flake = self;
+  };
+
   inherit (helpers.modules) evalNixvim;
 
   mkNvim =