[Rd] capture error messages from loading shared objects

[Henrik Bengtsson]

Careful; tryCatch() on non-error conditions will break out of what's
evaluated, e.g.

res <- tryCatch({
  cat("1\n")
  message("2")
  cat("3\n")
  42
}, message = identity)

will output '1' but not '3', because it returns as soon as the first
message() is called.

To "record" messages (same for warnings), use withCallingHandlers()
instead, e.g.

msgs <- list()
res <- withCallingHandlers({
  cat("1\n")
  message("2")
  cat("3\n")
  42
}, message = function(m) {
  msgs <<- c(msgs, list(m))
  invokeRestart("muffleMessage")
})

This will output '1', muffle '2', output '3', and return 42, and 'msgs' holds

> msgs
[[1]]
<simpleMessage in message("2"): 2

/Henrik

On Tue, Nov 28, 2023 at 10:34 AM Bill Dunlap <williamwdunlap using gmail.com> wrote:
>
> If you would like to save the error message instead of suppressing it, you
> can use tryCatch(message=function(e)e, ...).
>
> -BIll
>
> On Tue, Nov 28, 2023 at 3:55 AM Adrian Dusa <dusa.adrian using unibuc.ro> wrote:
>
> > Once again, Ivan, many thanks.
> > Yes, that does solve it.
> > Best wishes,
> > Adrian
> >
> > On Tue, Nov 28, 2023 at 11:28 AM Ivan Krylov <krylov.r00t using gmail.com>
> > wrote:
> >
> > > В Tue, 28 Nov 2023 10:46:45 +0100
> > > Adrian Dusa <dusa.adrian using unibuc.ro> пишет:
> > >
> > > > tryCatch(requireNamespace("foobar"), error = function(e) e)
> > >
> > > I think you meant loadNamespace() (which throws errors), not
> > > requireNamespace() (which internally uses tryCatch(loadNamespace(...))
> > > and may or may not print the error depending on the `quietly` argument).
> > >
> > > --
> > > Best regards,
> > > Ivan
> > >
> >
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> >
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