postgres: add an extensions option

[sandydoo]

This is a convenience option to install a list of PostgreSQL extensions. The set of available extensions is provided as an argument.

{
  services.postgres.enable = true;
  services.postgres.extensions = extensions: [ extensions.postgis ];
}

You could already do this by modifying the package with withPackages and then overriding services.postgres.package. The new option has two advantages over the existing approach:

1. It's easier to find in the documentation.

2. Users unfamiliar with nixpkgs are unlikely to be aware of
   pkgs.postgresql.withPackages specifically, or the pattern in
   general.

The NixOS services calls this option extraPlugins. First of all, that's not what PostgreSQL calls them. Second, you have to manually source the extensions from pkgs.postgresql.pkgs and ensure that the PostgreSQL version matches whatever is specified in services.postgres.package.

The description for the option contains a list of available extensions generated from the current version of PostgreSQL.

[cloudflare-pages]

Deploying with    Cloudflare Pages

Latest commit:	7e04f5c
Status:	✅  Deploy successful!
Preview URL:	https://358926f2.devenv.pages.dev
Branch Preview URL:	https://feature-postgres-extensions.devenv.pages.dev

View logs

[thenonameguy]

Great addition!

Just for fun I wrote an usage of this new option with some meta-programming to install all known working PG extensions for the selected cfg.package postgres version reliably.

{
  services.postgres = {
    enable = true;
    package = pkgs.postgresql_15;
    # install all extensions
    extensions =
      let
        filterBrokenAndNonHostPackages = hostPlatform: pkgs:
          lib.filterAttrs (name: pkg:
            !(pkg.meta ? broken && pkg.meta.broken) &&
            (pkg.meta ? platforms && lib.lists.elem hostPlatform pkg.meta.platforms)
          ) pkgs;
      in
        extensions: (lib.attrValues (filterBrokenAndNonHostPackages pkgs.system extensions));
  };
}

It might be worthwhile to use parts of the above code to only generate the extensions that are actually available into mkdocs, based on arch + postgres version used.

For an actually working version of above, I had to this on aarch64-darwin:

        extensions: (lib.attrValues
          (builtins.removeAttrs
            (filterBrokenAndNonHostPackages pkgs.system extensions)
            ["tds_fdw" "timescaledb_toolkit" "timescaldb-apache" "timescaledb"]));

[sandydoo]

@thenonameguy, very nice! 🙌