[Rd] capture error messages from loading shared objects

[Adrian Dușa]

Thanks Henrik and Bill,

Indeed, but I do have a function called tryCatchWEM() in package admisc
that captures all that.

My use case was to test for different architectures (for instance, arm64 vs
Intel MacOS) embedding R in cross-platform applications.
I needed to test if the package could be loaded, and previously used
requireNamespace() being unaware, as Ivan pointed out, that internally that
function already does tryCatch() with loadNamespace().

That was the reason why my own function tryCatchWEM() could not capture
that specific error message.
I now do:
> admisc::tryCatchWEM(loadNamespace("foobar"))
$error
[1] "there is no package called ‘foobar’"

(and the error message is captured just fine).

All the best,
Adrian

On Tue, Nov 28, 2023 at 7:45 PM Henrik Bengtsson <henrik.bengtsson using gmail.com>
wrote:

> 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
> > > >
> > >
> > >         [[alternative HTML version deleted]]
> > >
> > > ______________________________________________
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> > >
> >
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> >
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-- 
Adrian Dusa
University of Bucharest
Romanian Social Data Archive
Soseaua Panduri nr. 90-92
050663 Bucharest sector 5
Romania
https://adriandusa.eu

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