fish-shell/share/completions/which.fish

if which -v >/dev/null 2>/dev/null # GNU
    complete -c which -s a -l all -d "Print all matching executables in PATH, not just the first"
    complete -c which -s i -l read-alias -d "Read aliases from stdin, reporting matching ones on stdout"
    complete -c which -l skip-alias -d "Ignore option '--read-alias'"
    complete -c which -l read-functions -d "Read shell function definitions from stdin, reporting matching ones on stdout"
    complete -c which -l skip-functions -d "Ignore option '--read-functions'"
    complete -c which -l skip-dot -d "Skip dirs in PATH that start with a dot"
    complete -c which -l skip-tilde -d "Skip dirs in PATH that start with tilde and executables in \$HOME"
    complete -c which -l show-dot -d "For matches in PATH dirs that start with a dot, print './programname'"
    complete -c which -l show-tilde -d "Output a tilde when a dir matches the \$HOME"
    complete -c which -l tty-only -d "Stop processing options on the right if not on tty"
    complete -c which -s v -s V -l version -d "Display version and exit"
    complete -c which -l help -d "Display help and exit"
else # OSX
    complete -c which -s a -d "Print all matching executables in PATH, not just the first"
    complete -c which -s s -d "Print no output, only return 0 if found"
end

complete -c which -a "(__fish_complete_subcommand)" -x