Can an overlay know if it's in pkgs or pkgsMusl?

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1

I like this pattern:

  pkgs = import (fetchTarball
    "https://github.com/NixOS/nixpkgs/archive/nixos-23.11.tar.gz") {
      overlays =
        [ (self: super: { unstable = pkgs_unstable; }) (import ./overlay.nix) ];
    };

To add the unstable pkg set as an attribute to quickly get access to unstable packages.
My challenge is then in my overlay if I do the following:

self: super: {
   foo = super.unstable.foo;
}

I’m working in the pkgsMusl pkg set, then it seems like I am setting foo to be the glibc version.
(I think normally super would be the pkgsMusl attrset)

Is there a good way to handle this?

2

Does anyone else use this pattern btw?
i quite like it aside from this limitation.