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, 3 insertions, 1 deletions

diff --git a/lib/modules.nix b/lib/modules.nix
index 7f1646e9b8bc0..6a1b0bfdc4fa7 100644
--- a/lib/modules.nix
+++ b/lib/modules.nix
@@ -433,7 +433,9 @@ rec {
       # modules recursively. It returns the final list of unique-by-key modules
       filterModules = modulesPath: { disabled, modules }:
         let
-          moduleKey = m: if isString m then toString modulesPath + "/" + m else toString m;
+          moduleKey = m: if isString m && (builtins.substring 0 1 m != "/")
+            then toString modulesPath + "/" + m
+            else toString m;
           disabledKeys = map moduleKey disabled;
           keyFilter = filter (attrs: ! elem attrs.key disabledKeys);
         in map (attrs: attrs.module) (builtins.genericClosure {