feat: whatis recognizes section suffix (zdharma-continuum#45)

[F-Sy-H](https://github.com/zdharma-continuum/fast-syntax-highlighting) can recognize and highlight manual subsection suffixes (i.e., `open.2`, `ls.1p`, `printf.3`).

- `man-db` is known to support subsection suffixes
- `mandoc` should not be affected by this commit

→chroma/-whatis.ch

@@ -3,7 +3,18 @@
 
 (( next_word = 2 | 8192 ))
 local THEFD check __first_call="$1" __wrd="$2" __start_pos="$3" __end_pos="$4"
-local __style
+local __style __term __section __section_flag
+
+# extact manual subsection
+# NOTE: __term should be separated from __wrd to prevent incorrect cache hits
+if command -v mandb > /dev/null; then
+    __term="${__wrd%.[0-8n](|p|type|const|head|perl)}"
+    __section="${${2#$__term}#.}"
+else
+    __term=$__wrd
+fi
+
+[[ -n $__section ]] && __section_flag="-s $__section"
 
 (( ! ${+FAST_HIGHLIGHT[whatis_chroma_callback_was_ran]} )) && \
         FAST_HIGHLIGHT[whatis_chroma_callback_was_ran]=0
@@ -97,7 +108,7 @@ else
                 print "$__wrd"
                 (( __start=__start_pos-${#PREBUFFER}, __end=__end_pos-${#PREBUFFER} ))
                 print "$__start/$__end"
-                LANG=C whatis "$__wrd" 2>/dev/null
+                LANG=C whatis "${(z)__section_flag}" "$__term" 2>/dev/null
             )
             command true # see above
             zle -F ${${FAST_HIGHLIGHT[whatis_chroma_zle_-F_have_-w_opt]:#0}:+-w} "$THEFD" -fast-whatis-chroma-callback
@@ -107,7 +118,7 @@ else
                 print "$__wrd"
                 (( __start=__start_pos-${#PREBUFFER}, __end=__end_pos-${#PREBUFFER} ))
                 print "$__start/$__end"
-                LANG=C whatis "$__wrd" &> /dev/null
+                LANG=C whatis "${(z)__section_flag}" "$__term" &> /dev/null
                 print "$?"
             )
             command true