fish-shell/share/functions/__fish_complete_directories.fish

#
# Find directories that complete $argv[1], output them as completions
# with description $argv[2] if defined, otherwise use 'Directory'
#

function __fish_complete_directories -d "Complete using directories" --argument comp

    set desc (_ Directory)

    if test (count $argv) -gt 1
        set desc $argv[2]
    end

    eval "set dirs "$comp"*/"

    if test $dirs[1]
        printf "%s\t$desc\n" $dirs
    end

end