one thing that might be an issue: the ~/.confix/nixpkgs/config.nix file is probably generated by nixos - so in order to change it, you might need to:

1. comment the unfree packages
2. set the { nixpkgs.config.allowUnfree = true; }
3. rebuild switch
4. add the unfree packages
5. rebuild switch

I have to admit I haven't sussed the whole thing out either

one thing that might be an issue if you're on NixOS: the ~/.confix/nixpkgs/config.nix file is probably generated by nixos - so in order to change it, you might need to:

1. comment the unfree packages
2. set the { nixpkgs.config.allowUnfree = true; }
3. rebuild switch
4. add the unfree packages
5. rebuild switch

I have to admit I haven't sussed the whole thing out either

Is there any way to reference a flake input's original flakeRef?

idk why it isn't added to <flakeInput>.sourceInfo, but I'd like to actually know where the original destination of a flake is coming from

If I add this input

repo = {
    url = "path:/home/manu/.../repo";
    flake = false;
};

I can get the flake contents via
inputs.repo.outPath

{
  description = "OpenSSL version";
  inputs = {
    nixpkgs.url      = "github:NixOS/nixpkgs/nixos-unstable";
    flake-utils.url  = "github:numtide/flake-utils";
  };
  outputs = { self, nixpkgs, flake-utils, ... }:
    flake-utils.lib.eachDefaultSystem (system:
      let
        overlays = [ (final: prev: {
            openssl = prev.openssl.overrideAttrs (old: rec{
              version = "0.1";
              src = prev.pkgs.fetchurl {
                url = "https://www.openssl.org/source/openssl-${version}.tar.gz";
                hash = "";
              };
            });
          }) ];
        pkgs = import nixpkgs {
          inherit system overlays;
        };
      in
      with pkgs;
      {
        devShells.default = mkShell { buildInputs = [ openssl ]; };
      }
    );
}

{
  description = "OpenSSL version";
  inputs = {
    nixpkgs.url      = "github:NixOS/nixpkgs/nixos-unstable";
    flake-utils.url  = "github:numtide/flake-utils";
  };
  outputs = { self, nixpkgs, flake-utils, ... }:
    flake-utils.lib.eachDefaultSystem (system:
      let
        overlays = [ (final: prev: {
            openssl = prev.openssl.overrideAttrs (old: rec{
              version = "0.1";
              src = prev.pkgs.fetchurl {
                url = "https://www.openssl.org/source/openssl-${version}.tar.gz";
                hash = "";
              };
            });
          }) ];
        pkgs = import nixpkgs {
          inherit system overlays;
        };
      in
      with pkgs;
      {
        devShells.default = mkShell { buildInputs = [ openssl ]; };
      }
    );
}

otherwise, I would just go for:

        packages.default = pkgs.openssl.overrideAttrs (_old: rec {
          version = "0.1";
          src = pkgs.fetchurl { url = "https://www.openssl.org/source/openssl-${version}.tar.gz"; };
        });