clan-cli: shell completion for bash, zsh, fish

pkgs/clan-cli/shell.nix

@@ -41,6 +41,15 @@ let
 
       export PATH="$tmp_path/bin:${checkScript}/bin:$PATH"
       export PYTHONPATH="$repo_root:$tmp_path/${pythonWithDeps.sitePackages}"
+
+      export XDG_DATA_DIRS="$tmp_path/share''${XDG_DATA_DIRS:+:$XDG_DATA_DIRS}"
+      export fish_complete_path="$tmp_path/share/fish/vendor_completions.d''${fish_complete_path:+:$fish_complete_path}"
+      mkdir -p \
+        $tmp_path/share/fish/vendor_completions.d \
+        $tmp_path/share/bash-completion/completions \
+        $tmp_path/share/zsh/site-functions
+      register-python-argcomplete --shell fish clan > $tmp_path/share/fish/vendor_completions.d/clan.fish
+      register-python-argcomplete --shell bash clan > $tmp_path/share/bash-completion/completions/clan
     '';
   };
 in