[fish] Add an indicator to the prompt that shows there is a guix env

fish/.config/fish/config.fish

@@ -2,6 +2,37 @@ function fish_title
     prompt_pwd
 end
 
+function fish_prompt --description 'Write out the prompt'
+    set -l last_pipestatus $pipestatus
+    set -l normal (set_color normal)
+
+    # Color the prompt differently when we're root
+    set -l color_cwd $fish_color_cwd
+    set -l prefix
+    set -l suffix '>'
+    if contains -- $USER root toor
+        if set -q fish_color_cwd_root
+            set color_cwd $fish_color_cwd_root
+        end
+        set suffix '#'
+    end
+
+    # If we're running via SSH, change the host color.
+    set -l color_host $fish_color_host
+    if set -q SSH_TTY
+        set color_host $fish_color_host_remote
+    end
+
+    # Write pipestatus
+    set -l prompt_status (__fish_print_pipestatus " [" "]" "|" (set_color $fish_color_status) (set_color --bold $fish_color_status) $last_pipestatus)
+
+    if test -n "$GUIX_ENVIRONMENT"
+        echo -n "[env]"
+    end
+
+    echo -n -s (set_color $fish_color_user) "$USER" $normal @ (set_color $color_host) (prompt_hostname) $normal ' ' (set_color $color_cwd) (prompt_pwd) $normal (fish_vcs_prompt) $normal $prompt_status $suffix " "
+end
+
 function hc
     herbstclient $argv
 end