Put user-facing output under control of 'usethis.quiet' option

[jennybc]

Fixes #416 Need way to turn off messaging globally for usethis functions

Well, this was pretty satisfying!

I'm asking for review just to make sure I implemented as discussed and to see if there's anything else I can do along these lines to make life easier for someone using usethis in another package.

I'm also continuing to record implicit design principles explicitly in principles.md.

All of usethis's user-facing output goes through the cat_line() helper. I've put it under the control of a undocumented option "usethis.quiet".

So to use usethis functions quietly in a function do:

withr::local_options(list(usethis.quiet = TRUE))

cc @jimhester @isteves

[jimhester]

FWIW I don't agree with this principal, I think these status messages should be using message() (and stderr) and assuming RStudio / the Windows console did not re-color them I would push harder to make them use message().

If usethis was a normal unix program I would expect these user facing messages to be on stderr as they would be with message().

[jennybc]

Yeah, you are not wrong. I just wrote this down because Irene had asked (she's using usethis in the package for Tidies of March) and I decide to record the rationale, such as it is. This would not be hard to change, since everything is so centralized.

[jimhester]

Wonder if it would be worth promoting this to an argument (with the same default value), so you could call cat_line(quiet = FALSE). e.g.

cat_line <- function(..., quiet = getOption("usethis.quiet", default = FALSE)) {

Maybe only useful for internal testing in usethis, but I think it is a little more natural.

[jennybc]

For this to be productive internally, I'd need to add a quiet argument to todo() and done() and then this could happen in a few places:

Before:

if (!quiet) {
    done("Adding {collapse(value(new))} to {value(proj_rel_path(path))}")
}

After:

done("Adding {collapse(value(new))} to {value(proj_rel_path(path))}", quiet = quiet)

To be useful externally, I'd need to add quiet to user-facing use_*() functions.

But I see how that is a nicer definition of cat_line() itself, even if I don't do the other bits.

[jennybc]

And ... done.

[jennybc]

OK I did that, but one downside is that a future usethis developer could make a direct call to cat_line() and use quiet = FALSE argument and the "usethis.quiet = TRUE" option won't have the promised effect of silence. But presumably they'd either suffer immediately in tests or a downstream maintainer would raise a concern.