Add zsh completions

Signed-off-by: Nikolaos Karaolidis <nick@karaolidis.com>

hosts/common/configs/user/console/nix-direnv/default.nix

@@ -2,7 +2,7 @@
   user ? throw "user argument is required",
   home ? throw "home argument is required",
 }:
-{ inputs, ... }:
+{ lib, inputs, ... }:
 {
   home-manager.users.${user} = {
     programs = {
@@ -16,7 +16,9 @@
       zsh = {
         shellAliases.nde = "nix-direnv";
 
-        initExtra = ''
+        initExtra = let
+          devShells = lib.strings.concatStringsSep " " (lib.attrsets.mapAttrsToList (key: _: key) inputs.self.devShells);
+        in ''
           nix-direnv() {
             if [ -z "$1" ]; then
               echo "use flake" > .envrc
@@ -34,6 +36,13 @@
 
             direnv allow
           }
+
+          _nix-direnv-completion() {
+            local shells=(${devShells})
+            compadd -- $shells
+          }
+
+          compdef _nix-direnv-completion nix-direnv
         '';
 
         p10k.extraRightPromptElements = [ "direnv" ];