modules/context: flake option, provides access to our flake

modules/misc/context.nix

@@ -1,6 +1,20 @@
 { lib, ... }:
+let
+  isFlake = x: x._type or null == "flake";
+  flakeType = lib.types.addCheck lib.types.path isFlake // {
+    name = "flake";
+    description = "flake";
+  };
+in
 {
   options = {
+    flake = lib.mkOption {
+      type = flakeType;
+      description = ''
+        Nixvim's flake.
+      '';
+      internal = true;
+    };
     isTopLevel = lib.mkOption {
       type = lib.types.bool;
       default = false;

modules/top-level/nixpkgs.nix

@@ -129,7 +129,7 @@ in
     # NOTE: This is a nixvim-specific option; there's no equivalent in nixos
     source = lib.mkOption {
       type = lib.types.path;
-      # NOTE: default is only set if `flake` is passed to our lib
+      default = config.flake.inputs.nixpkgs;
       defaultText = lib.literalMD "Nixvim's flake `input.nixpkgs`";
       description = ''
         The path to import Nixpkgs from.