fish-shell/share/functions/__fish_parse_configure.fish

function __fish_parse_configure
	if test (count $argv) -ne 1
		echo "Usage: parse_configure path/to/configure" 1>&2
		return 1
	end

	# `complete` parses `./configure` as `configure` so we have to handle all paths, not just ./
	if not test -x $argv[1]
		printf "Cannot find or execute '%s'\n" $argv[1] 1>&2
		return 1
	end

    # Must support output along the lines of
    #  -h, --help              display this help and exit
    #      --help=short        display options specific to this package
    #      --help=recursive    display the short help of all the included packages
    #  -V, --version           display version information and exit
    #  -q, --quiet, --silent   do not print `checking ...' messages

	set -l next_line
	set -l line
	set -l buffer
	# Just fish's `./configure --help` takes ~350ms to run, before parsing
	# The following chain attempts to extract the help message:
	cat $argv[1] | tr \n \u0e | sed -n 's/.*Report the --help message\(.*\?\)ac_status.*/\1/; s/ac_status.*//p' | tr \u0e \n |
	while test "$next_line" != "" || read -lL next_line
		# In autoconfigure scripts, the first column wraps at 26 chars
		# echo next_line: $next_line
		# echo old_line: $line
		if test "$line" = ""
			set line $next_line
			set next_line "" # mark it as consumed
			continue
		else if string match -qr '^(   |\t){2,}[^-]\S*' -- $next_line
			# echo "continuation line found. Old value of line: " \"$line\"
			set line "$line "(string trim $next_line)
			set next_line "" # mark it as consumed
			continue
		end

		# echo line: $line

		# Search for one or more strings starting with `-` separated by commas
		if string replace -fr '^\s+(-.*?)\s+([^\s\-].*)' '$1\n$2' -- $line | read -lL opts description
			for opt in (string split -n , -- $opts | string trim)

				if string match -qr -- '--[a-z_0-9-]+=\[.*\]' $opt
					# --option=[OPTIONAL_VALUE]
					string replace -r -- '(--[a-z_0-9-]+)=.*' '$1' $opt | read opt
				else if string match -qr -- '--[a-z_0-9-]+\[=.*\]' $opt
					# --option[=OPTIONAL_VALUE]
					string replace -r -- '(--[a-z_0-9-]+)\[=.*' '$1' $opt | read opt
				else if string match -qr -- '--[a-z_0-9-]+=[A-Z]+' $opt
					# --option=CLASS_OF_VALUE (eg FILE or DIR)
					string replace -r -- '(--[a-z_0-9-]+)=.*' '$1' $opt | read opt
				else if string match -qr -- '--[a-z_0-9-]+=\S+' $opt
					# --option=literal_value, leave as-is
				else if string match -qr -- '--[a-z_0-9-]+$' $opt
					# long option, leave as-is
				else if string match -qr -- '-[^-]$' $opt
					# short option, leave as-is
				else
					continue
				end

				echo "$opt"\t"$description" # parsed by `complete` as value and description
			end
		end

		set line ""
	end
end