lib.modules: support strings with absolute paths in `disabledModules`

This is particularly useful for disabling modules defined in a flake.
Example:
disabledModules = [ "${flake}/modules/mymodule.nix" ];

Previously, absolute string paths were internally prepended with `modulesPath`,
which caused the module filtering to fail.

1 files changed, 5 insertions, 0 deletions

diff --git a/lib/tests/modules/disable-define-enable-string-path.nix b/lib/tests/modules/disable-define-enable-string-path.nix
new file mode 100644
index 0000000000000..6429a6d6354ae
--- /dev/null
+++ b/lib/tests/modules/disable-define-enable-string-path.nix
@@ -0,0 +1,5 @@
+{ lib, ... }:
+
+{
+  disabledModules = [ (toString ./define-enable.nix) ];
+}