Don't use conf-which for detecting if a depext CLI tool is installed

[MisterDA]

Hi! I just noticed that some packages use conf-which to detect if a depext CLI tool is installed. However, that isn't portable on platforms where there's no which tool (e.g., Windows). For instance the package conf-git does a which git to detect the presence of git, but a simpler git --version could do just fine.

[mseri]

Useful suggestion by @UnixJunkie using command -v: https://stackoverflow.com/questions/592620/how-can-i-check-if-a-program-exists-from-a-bash-script#677212

[MisterDA]

If we know that the program has a particular switch such as --version or --help and has a fast exit path when using that switch, I think it's better to use it instead of launching a shell just to test command -v, as it's a shell builtin. We don't have a "meta" package conf-command, we're creating packages for each program we may need, so that's more-or-less doable.

[mseri]

I agree, I added the link here as reference for the future for the packages where we cannot do that

[UnixJunkie]

Apparently, svm-train -h has an exit code of 1, so I did not want to use it. I guess that the exit code must be 0 so that opam will consider the command was found and is working. Hence, I used command -v, a bash shell builtin, since it is judged less evil than which, according to experts.

On Sat, Oct 9, 2021 at 12:26 AM Marcello Seri @.***> wrote:

I agree, I added the link here as reference for the future for the packages where we cannot do that

— You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub https://github.com/ocaml/opam-repository/issues/18452#issuecomment-938730593, or unsubscribe https://github.com/notifications/unsubscribe-auth/AAFUFAEB7ANUJ2PLPNVYQG3UF4ETNANCNFSM42OO5ZCQ . Triage notifications on the go with GitHub Mobile for iOS https://apps.apple.com/app/apple-store/id1477376905?ct=notification-email&mt=8&pt=524675 or Android https://play.google.com/store/apps/details?id=com.github.android&referrer=utm_campaign%3Dnotification-email%26utm_medium%3Demail%26utm_source%3Dgithub.

[MisterDA]

Must be the Season of the Which! (Debian is deprecating the which command, and in general Windows doesn't have it either (nor an unix shell)).

[MisterDA]

If we know that the program has a particular switch such as --version or --help and has a fast exit path when using that switch, I think it's better to use it instead of launching a shell just to test command -v, as it's a shell builtin.

I've just noticed that for conf-pkg-config.2 we're doing

build: [
  ["pkg-config" "--help"] {os != "openbsd"}
  ["/usr/local/bin/pkgconf" "--help"] {os = "openbsd"}
]

but that generates some noisy output! (the help text). I don't think there's a nice way to silence this (because Windows wouldn't like > /dev/null, or how would we know what shell is used?) so we should prefer --version over --help to have less noise.