Motivation for this change

with this change one can supply a httpd module as mediawiki.nix from outside of nixpkgs which makes extending httpd much easier during development and deployment:

example usage

  services.httpd = {
        enable = true;
        adminAddr = "admin@example.org";

        hostName = "example.org";
        extraSubservices =
        [ 
          { 
            serviceExpression=./httpd-module-nextcloud.nix;
            urlPrefix = "/nextcloud";
            dbPassword = "hallo";
            adminPassword = "mysuperpassword";
            trustedDomain="example.org";
          }
        ];
      };
  ...

note: this change only extends httpd abstraction and also changes the precedence: svc.function > serviceExpression > serviceType

this patch is a huge relief as it makes httpd extensions trivial and one does not have to manage a nixpkgs checkout for simple httpd module tests/extensions.

Things done

• Tested using sandboxing
  (nix.useSandbox on NixOS,
  or option build-use-sandbox in nix.conf
  on non-NixOS)
• Built on platform(s)
  • NixOS
  • OS X
  • Linux
• Tested compilation of all pkgs that depend on this change using nix-shell -p nox --run "nox-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Fits CONTRIBUTING.md.