`show_messages=FALSE` only suppresses `stderr`

[andrjohns]

A request that's come up in the BDA course is the ability to supress all output from a $sample() run. At the moment, the best that can be done with show_messages=FALSE and refresh=0 is:

Running MCMC with 4 sequential chains...

Chain 1 finished in 0.1 seconds.
Chain 2 finished in 0.1 seconds.
Chain 3 finished in 0.1 seconds.
Chain 4 finished in 0.1 seconds.

All 4 chains finished successfully.
Mean chain execution time: 0.1 seconds.
Total execution time: 0.8 seconds.

Which I believe is because show_messages doesn't suppress stdout as well. Could be good to either add that as part of the behaviour of show_messages or to add an additional setting to supress all output

[rok-cesnovar]

I think what we want to do is rethink logging and make a "logging" argument that behaves something along these lines:

• default TRUE -> log everything
• FALSE -> log nothing at all
• "exceptions-only -> show cmdstan exceptions
• "progress-only" -> show progress and end timings only.

This is a duplicate of #646, but we can keep it as I think this has to be done sooner rather than later :)

[jgabry]

I agree this would be nice. I like @rok-cesnovar's logging idea.

[jgabry]

Should we close this now that #746 was merged a while ago and we have show_exceptions? Or do we still want to eventually add a "logging" argument? If the latter we can keep this open.

[jgabry]

Closing this since we have #746. If we want to add additional logging features (I'm open to that) we can open new issues.