Rewrite __fish_print_help to produce better results

As a result of this rewrite, the output now:

* Expands to fit the terminal width, like `man` does
* Preprocesses the manpage with `tbl` just in case, since `man` does
  this, even though I doubt any fish manpages use `tbl` formatting.
* Handle bold/underline with the `ul` command as it was designed for
  instead of trying to fake it with `sed`.
* Compresses blank lines as `man` does with the default `less -is`
  pager.

share/functions/__fish_print_help.fish

@@ -1,12 +1,6 @@
-
 function __fish_print_help --description "Print help message for the specified fish function or builtin" --argument item
-
-	switch $argv[1]
-		case '.'
+	if test "$item" = '.'
 		set item source
-
-		case '*'
-		set item $argv[1]
 	end
 
 	# Do nothing if the file does not exist
@@ -14,27 +8,81 @@ function __fish_print_help --description "Print help message for the specified f
 		return
 	end
 
-	# These two expressions take care of underlines (Should be italic)
-	set -l cmd1 s/_\x08'\(.\)'/(set_color --underline)\\1(set_color normal)/g
-	set -l cmd2 s/'\(.\)'\x08_/(set_color --underline)\\1(set_color normal)/g
-
-	# This expression should take care of bold characters. It's not
-	# waterproof, since it doesn't check that the same character is
-	# used both before and after the backspace, since regular
-	# languages don't allow backreferences.
-	set -l cmd3 s/.\x08'\(.\)'/(set_color --bold)\\1(set_color normal)/g
-
-	# Combine all expressions in a single variable
-	set -l sed_cmd -e $cmd1 -e $cmd2 -e $cmd3
+	set -l IFS \n\ \t
 
 	# Render help output, save output into the variable 'help'
-	set -l help (nroff -man "$__fish_datadir/man/man1/$item.1" ^ /dev/null )
-	set -l lines (count $help)
+	set -l help
+	set -l rLL
+	if command test -t 1
+		# We want to simulate `man`'s dynamic line length, because
+		# defaulting to 80 kind of sucks.
+		# Note: using `command test` instead of `test` because `test -t 1`
+		# doesn't seem to work right.
+		# Note: grab the size from the stdout terminal in case it's somehow
+		# different than the stdin of fish.
+		set -l cols
+		begin
+			# use fd 3 to copy our stdout because we need to pipe the output of stty
+			stty size 0<&3 | read _ cols
+		end 3<&1
+		set cols (expr $cols - 4) # leave a bit of space on the right
+		set rLL -rLL=$cols[1]n
+	end
+	set help (nroff -man -t $rLL "$__fish_datadir/man/man1/$item.1" ^/dev/null)
 
-	# Print an empty line first
-	echo
-
-	# Filter and print help
-	printf "%s\n" $help| tail -n (expr $lines - 5) | head -n (expr $lines - 8) | sed $sed_cmd
+	# The original implementation trimmed off the top 5 lines and bottom 3 lines
+	# from the nroff output. Perhaps that's reliable, but the magic numbers make
+	# me extremely nervous. Instead, let's just strip out any lines that start
+	# in the first column. "normal" manpages put all section headers in the first
+	# column, but fish manpages only leave NAME like that, which we want to trim
+	# away anyway.
+	#
+	# While we're at it, let's compress sequences of blank lines down to a single
+	# blank line, to duplicate the default behavior of `man`, or more accurately,
+	# the `-s` flag to `less` that `man` passes.
+	set -l state blank
+	for line in $help
+		# categorize the line
+		set -l line_type
+		switch $line
+		case ' *' \t\*
+			# starts with whitespace, check if it has non-whitespace
+			printf "%s\n" $line | read -l word _
+			if test -n $word
+				set line_type normal
+			else
+				# lines with just spaces probably shouldn't happen
+				# but let's consider them to be blank
+				set line_type blank
+			end
+		case ''
+			set line_type blank
+		case '*'
+			# not leading space, and not empty, so must contain a non-space
+			# in the first column. That makes it a header/footer.
+			set line_type meta
+		end
 
+		switch $state
+		case normal
+			switch $line_type
+			case normal
+				printf "%s\n" $line
+			case blank
+				set state blank
+			case meta
+				# skip it
+			end
+		case blank
+			switch $line_type
+			case normal
+				echo # print the blank line
+				printf "%s\n" $line
+				set state normal
+			case blank meta
+				# skip it
+			end
+		end
+	end | ul # post-process with `ul`, to interpret the old-style grotty escapes
+	echo # print a trailing blank line
 end