Optimize hg prompt

Mainly replace hg calls since python is slow to start.

share/functions/__fish_hg_prompt.fish

@@ -27,23 +27,32 @@ function __fish_hg_prompt --description 'Write out the hg prompt'
 		return 1
 	end
 
-    set -l branch (hg branch ^/dev/null)
-	# If there's no branch, there's no repository
-    if test -z $branch
-        return
+	# Find an hg directory above $PWD
+	# without calling `hg root` because that's too slow
+	set -l root
+	set -l dir $PWD
+    while test $dir != "/"
+      if test -f $dir'/.hg/dirstate'
+        set root $dir"/.hg"
+		break
+      end
+	  # Go up one directory
+	  set -l dir (string replace -r '[^/]*/?$' '' $dir)
     end
 
-	# With "-q", hg bookmark will always output every bookmark
-	# So our only option is to filter it ourselves
-	set -l bookmark (hg bookmark | string match ' \\**' | cut -d" " -f3)
-	# Unfortunately, hg bookmark doesn't exit non-zero when there's no bookmark
-	if test -n "$bookmark"
+	if test -z "$root"
+		return 0
+	end
+
+	# Read branch and bookmark
+    set -l branch (cat $root/branch ^/dev/null; or echo default)
+	if set -l bookmark (cat $root/bookmarks.current ^/dev/null)
 		set branch "$branch/$bookmark"
 	end
 
     echo -n '|'
 
-    set -l repo_status (hg status | cut -c 1-2 | sort -u)
+    set -l repo_status (hg status | string sub -l 2 | sort -u)
 
     # Show nice color for a clean repo
     if test -z "$repo_status"