Merge pull request #57 from DeterminateSystems/relax-overlay-check

edolstra · web-flow · commit c4e68a971a04 · 2026-03-17T18:57:03.000+01:00
Don't try to call the overlay function
diff --git a/flake.nix b/flake.nix
@@ -258,9 +258,9 @@
                 # flake here. Maybe this schema should be moved to the
                 # nixpkgs flake, where it does have access.
                 if !builtins.isFunction overlay then
-                  throw "overlay is not a function, but a set instead"
+                  throw "Overlay is not a function. It should be structured like: `final: previous: { /* ... */ }`."
                 else
-                  builtins.isAttrs (overlay { } { });
+                  true;
             }) output
           );
       };
diff --git a/tests/overlays.json b/tests/overlays.json
@@ -0,0 +1,15 @@
+{
+  "inventory": {
+    "overlays": {
+      "doc": "The `overlays` flake output defines [\"overlays\"](https://nixos.org/manual/nixpkgs/stable/#chap-overlays) that can be plugged into Nixpkgs.\nOverlays add additional packages or modify or replace existing packages.\n",
+      "output": {
+        "children": {
+          "example": {
+            "what": "Nixpkgs overlay"
+          }
+        }
+      }
+    }
+  },
+  "version": 2
+}
diff --git a/tests/overlays/flake.nix b/tests/overlays/flake.nix
@@ -0,0 +1,12 @@
+{
+  outputs =
+    { ... }:
+    {
+      overlays.example =
+        final:
+        { foo, ... }:
+        {
+          inherit foo;
+        };
+    };
+}
