Use mandoc when nroff not available

mandoc users do not need to install nroff to be able to format and view
manual pages. If both nroff and mandoc cannot be found it will show an
error.

CHANGELOG.md

@@ -13,6 +13,7 @@
  - nothing yet...
 - Lots of improvements to completions.
 - fish_clipboard_* now supports wayland by means of [wl-clipboard](https://github.com/bugaevc/wl-clipboard).
+- mandoc can now be used to format the output from `--help` if nroff is not installed
 
 ---
 

share/functions/__fish_print_help.fish

@@ -10,21 +10,35 @@ function __fish_print_help --description "Print help message for the specified f
 
     # Render help output, save output into the variable 'help'
     set -l help
-    set -l cols $COLUMNS
-    set -l rLL
-    if test -n "$cols"
-        set cols (math $cols - 4) # leave a bit of space on the right
-        set rLL -rLL=$cols[1]n
+    set -l format
+    set -l cols
+    if test -n "$COLUMNS"
+        set cols (math $COLUMNS - 4) # leave a bit of space on the right
     end
-    set -lx GROFF_TMAC_PATH $__fish_data_dir/groff
-    set -l mfish
-    if test -e $GROFF_TMAC_PATH/fish.tmac
-        set mfish -mfish
+
+    # Pick which command we are using to render output or fail if none
+    if command -qs nroff
+        set format nroff -c -man -t
+        if test -e $__fish_data_dir/groff/fish.tmac
+            set -a format -M$__fish_data_dir/groff -mfish
+        end
+        if test -n "$cols"
+            set -a format -rLL={$cols}n
+        end
+    else if command -qs mandoc
+        set format mandoc -c
+        if test -n "$cols"
+            set -a format -O width=$cols
+        end
+    else
+        echo fish: (_ "Cannot format help; no parser found")
+        return 1
     end
+
     if test -e "$__fish_data_dir/man/man1/$item.1"
-        set help (nroff -c -man $mfish -t $rLL "$__fish_data_dir/man/man1/$item.1" 2>/dev/null)
+        set help ($format "$__fish_data_dir/man/man1/$item.1" 2>/dev/null)
     else if test -e "$__fish_data_dir/man/man1/$item.1.gz"
-        set help (gunzip -c "$__fish_data_dir/man/man1/$item.1.gz" 2>/dev/null | nroff -c -man $mfish -t $rLL 2>/dev/null)
+        set help (gunzip -c "$__fish_data_dir/man/man1/$item.1.gz" 2>/dev/null | $format 2>/dev/null)
     end
 
     # The original implementation trimmed off the top 5 lines and bottom 3 lines