When having a patch for a python module that should only be used for
mailman, but for nothing else, it's now possible to apply it like this:
self: super: {
mailmanPackages = super.mailmanPackages.extend (mailmanSelf: mailmanSuper: {
python3 = mailmanSuper.python3.override {
overlay = pythonSelf: pythonSuper: {
psycopg2 = /* ... */;
};
};
});
}
The underlying issue is that the `packageOverrides`-mechanism of
`pkgs.python3` doesn't compose, so an optional overlay is manually
applied to the `python3` used for mailman.
2cefe69f6f