Add a couple of extra checks to exportOverlays function

lib/exportOverlays.nix

@@ -44,27 +44,43 @@ let
         attrNames
         attrValues
         concatMap
+        concatStringsSep
         elem
         filter
         foldl'
         head
+        isAttrs
+        isFunction
         listToAttrs
         mapAttrs
+        tryEval
         ;
+
+      # Hopefully will fix a couple of edge cases. Even tho `lib` is defined as API here - it is not. Do not use it.
+      fakePkgs = {
+        lib = flake-utils-plus.lib.internal;
+        callPackage = it: it;
+        isFakePkgs = true; # Overlay maintainers may throw an exception in case this key is set in case overlay is not compatible with this function.
+      };
+
       nameValuePair = name: value: { inherit name value; };
 
       # just pull out one arch from the system-spaced pkgs to get access to channels
       # overlays can be safely evaluated on any arch
       channels = head (attrValues pkgs);
 
-      pathStr = path: builtins.concatStringsSep "/" path;
+      pathStr = path: concatStringsSep "/" path;
 
-      channelNames = attrNames channels;
-      overlayNames = overlay: attrNames (overlay null null);
+      overlayNames = overlay:
+        if isOverlay overlay
+        then attrNames (overlay fakePkgs fakePkgs)
+        else [ ];
+
+      isOverlay = it: isFunction it && isFunction (it fakePkgs) && (tryEval (isAttrs (it fakePkgs fakePkgs))).success;
 
       # get all overlays from inputs
       inputOverlays = mapAttrs
-        (_: v: [ v.overlay or (_: _: { }) ] ++ attrValues v.overlays or { })
+        (_: v: (if isOverlay (v.overlay or null) then [ v.overlay ] else [ ]) ++ (filter isOverlay (attrValues (v.overlays or { }))))
         (removeAttrs inputs [ "self" ]);
       # use overlayNames as a way to identify overlays
       flattenedInputOverlays = map overlayNames (foldl' (a: b: a ++ b) [ ] (attrValues inputOverlays));
@@ -96,7 +112,7 @@ let
             )
             (filterOverlays channels.${channelName})
         )
-        channelNames
+        (attrNames channels)
     );
 
 in

lib/internal-functions.nix

@@ -12,6 +12,8 @@ rec {
   */
   genAttrs' = func: values: builtins.listToAttrs (map func values);
 
+  getAttrs = names: attrs: genAttrs names (name: attrs.${name});
+
   hasFileAttr = o: builtins.hasAttr "_file" o;
 
   # Definition in nixpkgs

tests/export-overlays/flake.nix

@@ -0,0 +1,18 @@
+{
+  inputs.utils.url = "/home/gytis/Projects/flake-utils-plus";
+  inputs.neovitality.url = github:vi-tality/neovitality/69aaf582bf46992ae10e6aaa44f37c9d4096cc38; # As of writing contains invalid `overlays` attribute.
+  inputs.nixpkgs.url = github:NixOS/nixpkgs;
+
+  outputs = inputs@{ self, neovitality, utils, ... }:
+    utils.lib.mkFlake {
+      inherit self inputs;
+      supportedSystems = [ "x86_64-linux" "x86_64-darwin" "aarch64-linux" ];
+
+      overlays = utils.lib.exportOverlays { inherit (self) pkgs inputs; };
+
+    };
+}
+
+
+
+

tests/overlays-flow/flake.nix

@@ -90,6 +90,3 @@
     };
 }
 
-
-
-