{
    url ? "https://github.com/NixOS/nixpkgs.git",
    rev ? "ac05d50ffe6e11d962c979c1171a8cd43d79e574",
    sha256 ? "07iyfki7qdsqa7c61lfnw0wx2pca71li9bh633v7zra84b8a0xhs",
    overlays ? []
}:
let _nixpkgs = (import <nixpkgs> {});
in
(import (_nixpkgs.fetchgit { inherit url rev sha256; }) {
    overlays = [
        (self: super: {
            postgresql = self.postgresql_12;
        })
    ] ++ overlays ++ [
        (self: super: {
            postgresql = super.postgresql.overrideAttrs (super: rec {
                ...
            });
        })
    ];
})

xpkgs.config.permittedInsecurePackages = [
         "openssl-1.0.2u"
       ];

{
    url ? "https://github.com/NixOS/nixpkgs.git",
    rev ? "ac05d50ffe6e11d962c979c1171a8cd43d79e574",
    sha256 ? "07iyfki7qdsqa7c61lfnw0wx2pca71li9bh633v7zra84b8a0xhs",
    overlays ? []
}:
let _nixpkgs = ( import <nixpkgs> { } );
in
(import (_nixpkgs.fetchgit { inherit url rev sha256; }) {
    config.permittedInsecurePackages = [ "openssl-1.0.2u" ]; 
    overlays = [
        (self: super: {
            postgresql = self.postgresql_12;
        })
    ] ++ overlays ++ [
        (self: super: {
            postgresql = super.postgresql.overrideAttrs (super: rec {
                # remove this patch that changes socket dir from /tmp to /run/postgresql since the latter requires root
                patches = (builtins.filter (x: (builtins.baseNameOf x) != "socketdir-in-run.patch") super.patches);

                # This overrides producing multiple store paths (out, lib, doc, man) instead of just one.
                # Multiple store paths breaks pg_config behavior where it will output directories relative to the
                # binary that was invoked (supporting relocating binaries, which we need). In particular,
                # pg_config --libdir would point to the nix store path instead of our libdir, breaking support for
                # installing extensions which require a mutable libdir. This also fixes pg_config --docdir,
                # pg_config --htmldir, and pg_config --pkglibdir output.
                outputs = [ "out" ];
                configureFlags = (builtins.filter (x: x != "--libdir=$(lib)/lib") super.configureFlags) ++ [
                    # "--with-llvm"
                    "--with-python"
                    "--with-perl"
                    "--with-tcl"
                    "--with-segsize=16"
                    "--with-blocksize=8"
                ];
                buildInputs = super.buildInputs ++ (with self; [
                    # clang
                    # llvm
                    perl
                    python
                    tcl
                ]);
            });
        })
    ];
})