lib/modules: Use fixed lib instead of args.lib

The practical use for this should be very limited because I don't
think anyone should change `lib`, let alone change `lib.functionArgs`,
but, but it would be even stranger to rely on `args.lib` (or really
`specialArgs.lib` for what's clearly a behavior of the current
`evalModules`, which uses its own ambient lib for basically everything.

The shadowing of `lib` by `args.lib` here seems to be a small mistake,
which is easy to make.

lib/modules.nix

@@ -485,10 +485,10 @@ let
         config = addFreeformType (removeAttrs m ["_class" "_file" "key" "disabledModules" "require" "imports" "freeformType"]);
       };
 
-  applyModuleArgsIfFunction = key: f: args@{ config, options, lib, ... }:
+  applyModuleArgsIfFunction = key: f: args@{ config, ... }:
     if isFunction f then applyModuleArgs key f args else f;
 
-  applyModuleArgs = key: f: args@{ config, options, lib, ... }:
+  applyModuleArgs = key: f: args@{ config, ... }:
     let
       # Module arguments are resolved in a strict manner when attribute set
       # deconstruction is used.  As the arguments are now defined with the

lib/tests/modules.sh

@@ -94,6 +94,8 @@ checkConfigOutput '^true$' config.result ./module-argument-default.nix
 # gvariant
 checkConfigOutput '^true$' config.assertion ./gvariant.nix
 
+checkConfigOutput '"ok"' config.result ./specialArgs-lib.nix
+
 # https://github.com/NixOS/nixpkgs/pull/131205
 # We currently throw this error already in `config`, but throwing in `config.wrong1` would be acceptable.
 checkConfigError 'It seems as if you.re trying to declare an option by placing it into .config. rather than .options.' config.wrong1 ./error-mkOption-in-config.nix

lib/tests/modules/specialArgs-lib.nix

@@ -0,0 +1,28 @@
+{ config, lib, ... }:
+
+{
+  options = {
+    result = lib.mkOption { };
+    weird = lib.mkOption {
+      type = lib.types.submoduleWith {
+        # I generally recommend against overriding lib, because that leads to
+        # slightly incompatible dialects of the module system.
+        # Nonetheless, it's worth guarding the property that the module system
+        # evaluates with a completely custom lib, as a matter of separation of
+        # concerns.
+        specialArgs.lib = { };
+        modules = [ ];
+      };
+    };
+  };
+  config.weird = args@{ ... /* note the lack of a `lib` argument */ }:
+  assert args.lib == { };
+  assert args.specialArgs == { lib = { }; };
+  {
+    options.foo = lib.mkOption { };
+    config.foo = lib.mkIf true "alright";
+  };
+  config.result =
+    assert config.weird.foo == "alright";
+    "ok";
+}