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