Move xonsh customization to an overlay

nix/overlays/xonsh.nix

@@ -0,0 +1,44 @@
+final: prev: {
+  # xonsh = prev.xonsh.overrideAttrs (old: rec {
+  #   version = "0.12.4";
+  #   src = final.fetchFromGitHub {
+  #     owner = "xonsh";
+  #     repo = "xonsh";
+  #     rev = version;
+  #     sha256 = "0kdps0gf0767zy0fs6qn39rv4z3x7ck0qz1pzx6962593171yk8b";
+  #   };
+  #   propagatedBuildInputs = prev.xonsh.propagatedBuildInputs ++ [final.python3Packages.virtualenv];
+  # });
+
+  python = prev.python.override {
+    packageOverrides = pfinal: pprev: {
+      prompt-toolkit = pprev.prompt-toolkit.overrideAttrs (old: rec {
+        version = "3.0.29";
+        src = pfinal.fetchPypi {
+          pname = "prompt_toolkit";
+          inherit version;
+          sha256 = "";
+        };
+      });
+    };
+  };
+
+  # Mach-nix is a toolkit for constructing custom Python environments
+  mach-nix = import (builtins.fetchGit {
+    url = "https://github.com/DavHau/mach-nix/";
+    ref = "refs/tags/3.4.0";
+  }) {
+    pkgs = final;
+  };
+
+  xonsh_pyenv = final.mach-nix.mkPython {
+    requirements = ''
+    xontrib-fzf-widgets
+    xonsh-direnv
+    '';
+  };
+
+  xonsh_with_plugins = final.xonsh.overrideAttrs (old: {
+    propagatedBuildInputs = old.propagatedBuildInputs ++ final.xonsh_pyenv.python.pkgs.selectPkgs final.xonsh_pyenv.python.pkgs;
+  });
+}