mailman: init package for Mailman CLI

We already had python3Packages.mailman, but that's only really usable
as a library.  The only other option was to create a whole Python
environment, which was undesirable to install as a system-wide
package.

pkgs/servers/mail/mailman/default.nix

@@ -28,15 +28,12 @@ buildPythonPackage rec {
   '';
 
   # Mailman assumes that those scripts in $out/bin are Python scripts. Wrapping
-  # them in shell code breaks this assumption. The proper way to use mailman is
-  # to create a specialized python interpreter:
-  #
-  #   python37.withPackages (ps: [ps.mailman])
+  # them in shell code breaks this assumption. Use the wrapped version (see
+  # wrapped.nix) if you need the CLI (rather than the Python library).
   #
   # This gives a properly wrapped 'mailman' command plus an interpreter that
   # has all the necessary search paths to execute unwrapped 'master' and
-  # 'runner' scripts. The setup is a little tricky, but fortunately NixOS is
-  # about to get a OS module that takes care of those details.
+  # 'runner' scripts.
   dontWrapPythonPrograms = true;
 
   meta = {

pkgs/servers/mail/mailman/wrapped.nix

@@ -0,0 +1,20 @@
+{ runCommand, lib, makeWrapper, python3
+, archivers ? [ python3.pkgs.mailman-hyperkitty ]
+}:
+
+let
+  inherit (python3.pkgs) makePythonPath mailman;
+in
+
+runCommand "${mailman.name}-wrapped" {
+  inherit (mailman) meta;
+  buildInputs = [ makeWrapper ];
+  passthru = mailman.passthru // { unwrapped = mailman; };
+} ''
+  mkdir -p "$out/bin"
+  cd "${mailman}/bin"
+  for exe in *; do
+    makeWrapper "${mailman}/bin/$exe" "$out/bin/$exe" \
+        --set PYTHONPATH ${makePythonPath ([ mailman ] ++ archivers)}
+  done
+''