zsh: Make nix-shell pretty and update ps1

users/hu/packages/zsh/config/conf.d/ps1.zsh

@@ -9,10 +9,21 @@ case "$distro" in
     *) dicon="%F{yellow}[󰘧]%f" ;;
 esac
 
+if [ -n "$IN_NIX_SHELL" ]; then
+    if [ -z "$NIX_SHELL_PACKAGES" ]; then
+        nix_shell_ps1="%F{red}nix-shell%f"
+    else
+        nix_shell_ps1="%F{red}{ $NIX_SHELL_PACKAGES }%f"
+    fi
+else
+    nix_shell_ps1=""
+fi
+
 setopt prompt_subst
 autoload -Uz vcs_info
 precmd () { vcs_info }
-zstyle ':vcs_info:*' formats ' %F{yellow}(%b)%f'
+zstyle ':vcs_info:*' formats ' %F{yellow}(%b)%f '
 
-export PS1='$dicon %n@%m %F{green}%~%f$vcs_info_msg_0_> '
+NL=$'\n'
+export PS1='%F{green}%~%f$vcs_info_msg_0_$nix_shell_ps1$NL$dicon > '