python3.pkgs.invoke: install shell completions

pkgs/development/python-modules/invoke/default.nix

@@ -2,7 +2,7 @@
 , bash
 , buildPythonPackage
 , fetchPypi
-, pythonOlder
+, stdenv
 }:
 
 buildPythonPackage rec {
@@ -26,6 +26,13 @@ buildPythonPackage rec {
     "invoke"
   ];
 
+  postInstall = lib.optionalString (stdenv.buildPlatform.canExecute stdenv.hostPlatform) ''
+    mkdir -p $out/share/{bash-completion/completions,fish/vendor_completions.d,zsh/site-functions}
+    $out/bin/inv --print-completion-script=zsh >$out/share/zsh/site-functions/_inv
+    $out/bin/inv --print-completion-script=bash >$out/share/bash-completion/completions/inv.bash
+    $out/bin/inv --print-completion-script=fish >$out/share/fish/vendor_completions.d/inv.fish
+  '';
+
   meta = with lib; {
     description = "Pythonic task execution";
     homepage = "https://www.pyinvoke.org/";