opam list --silent should be --check

[dra27]

For better or worse, the option added in #3533 should more consistently have been --check (display nothing, communicate in exit code only). This can be renamed for 2.1 using CLI versioning.

[rjbou]

It should be --check-[package-existence], because opam list isn't supposed to check things, it can be not obvious what is checked.

[AltGr]

Just to add some inputs, this is from the grep manpage:

       -q, --quiet, --silent
              Quiet; do not write anything to standard output.  Exit immediately with zero status if any match is found, even if an error was detected.  Also see the -s or --no-messages option.
       -c, --count
              Suppress normal output; instead print a count of matching lines for each input file.  With the -v, --invert-match option (see below), count non-matching lines.

[kit-ty-kate]

I think --silent is an ok name and i agree with @AltGr it matches up with grep.
In my opinion, --check would not be a good name because if I were just to read the command (e.g. opam list --check --installable --depends-on pkg) I would instinctively think the --check command is just there to do extra checks or something, not that it would not write anything to stdout.

Personally I would be in favour of closing this issue.

[dra27]

I don't recall if this arose from a discussion, or just from the complete review of the CLI options added since 2.0 which I did when adding CLI versioning, but closing this doesn't resolve the inconsistency between opam {update,install,env} --check with opam list --check inexplicably called opam list --silent... for comparing other CLIs, cf. *sum --check, but the concern was having two names in different parts of the CLI for the same function.