Ah:

          src = if version != "" then pkgs.fetchurl {
            url = "https://www.openssl.org/source/openssl-${version}.tar.gz";
            hash = hash;
          } else
          prev.src;

does the job.

Btw. regarding override and overrideAttrs is there some common patterns to follow? I need both so did something like:

package = ( pkgs.package.override { param = 1 } ).overrideAttrs (final: prev: { ... });

How can I map over types.attrsOf option in config. Example:

{ config, lib, ... }:
with lib;

{
  options = {
    users = mkOption {
      type = types.attrsOf (types.submodule ({ ... }: {
        options = {
          foo = mkEnableOption "foo";
          bar = mkEnableOption "bar";
        };
      }));
      default = {};
    };
  };
}

How can I do something like users.<user>.foo = mkIf config.users.<user>.bar true for every <user>?

I've tried

    users = flip mapAttrs config.users (name: user: {
      foo = mkIf user.bar true;
    });

but this gives me infinite recursion error.

How can I map over types.attrsOf option in config. Example:

{ config, lib, ... }:
with lib;

{
  options = {
    users = mkOption {
      type = types.attrsOf (types.submodule ({ ... }: {
        options = {
          foo = mkEnableOption "foo";
          bar = mkEnableOption "bar";
        };
      }));
      default = {};
    };
  };
}

How can I do something like users.<user>.foo = mkIf config.users.<user>.bar true for every <user>?

I've tried

    users = flip mapAttrs config.users (name: user: {
      foo = mkIf user.bar true;
    });

but this gives me infinite recursion error.

In reply to @ity:itycodes.org
Does this answer your Q?

No. I don't know the users a prori. The users of the module can use anything, e.g. someone could configure it like.

{
  users.alice = { foo = true; }
  users.bob = { bar = true; }
}

And with this example I wold want it to evaluate to

{
  users.alice.foo = true;
  users.alice.bar = false;
  users.bob.foo = true;
  users.bob.bar = true;

In reply to @ity:itycodes.org
Does this answer your Q?

No. I don't know the users a prori. The users of the module can use anything, e.g. someone could configure it like.

{
  users.alice = { foo = true; }
  users.bob = { bar = true; }
}

And with this example I wold want it to evaluate to

{
  users.alice.foo = true;
  users.alice.bar = false;
  users.bob.foo = true;
  users.bob.bar = true;

No. I don't know the users a prori. The users of the module can use anything, e.g. someone could configure it like.

{
  users.alice = { foo = true; }
  users.bob = { bar = true; }
}

And with this example I wold want it to evaluate to

{
  users.alice.foo = true;
  users.alice.bar = false;
  users.bob.foo = true;
  users.bob.bar = true;
}

In reply to @ity:itycodes.org
Why is foo for bob true while bar for alice is false

But I've managed to figure it out:

{ config, lib, ... }:
with lib;

{
  options = {
    users = mkOption {
      type = types.attrsOf (types.submodule (args: let user = args.config; in {
        options = {
          foo = mkEnableOption "foo";
          bar = mkEnableOption "bar";
        };
        config = {
          foo = mkIf user.bar true;
        };
      }));
      default = {};
    };
  };
}