[Rd] DOCS: Exactly when, in the signaling process, is option 'warn' applied?

Henrik Bengtsson henr|k@bengt@@on @end|ng |rom gm@||@com
Thu Nov 18 18:43:29 CET 2021


the following question sprung out of a package settings option warn=-1
to silence warnings, but those warnings were still caught by
withCallingHandlers(..., warning), which the package author did not
anticipate. The package has been updated to use suppressWarnings()
instead, but as I see a lot of packages on CRAN [1] use
options(warn=-1) to temporarily silence warnings, I wanted to bring
this one up. Even base R itself [2] does this, e.g.

Exactly when is the value of 'warn' options used when calling warning("boom")?

I think the docs, including ?options, would benefit from clarifying
that. To the best of my understanding, it should also mention that
options 'warn' is meant to be used by end-users, and not in package
code where suppressWarnings() should be used.

To clarify, if we do:

> options(warn = -1)
> tryCatch(warning("boom"), warning = function(w) stop("Caught warning: ", conditionMessage(w), call. = FALSE))
Error: Caught warning: boom

we see that the warning is indeed signaled.  However, in Section '8.2
warning' of the 'R Language Definition' [3], we can read:

"The function `warning` takes a single argument that is a character
string. The behaviour of a call to `warning` depends on the value of
the option `"warn"`. If `"warn"` is negative warnings are ignored.

The way this is written, it may suggest that warnings are
ignored/silences already early on when calling warning(), but the
above example shows that that is not the case.

>From the same section, we can also read:

"[...] If it is zero, they are stored and printed after the top-level
function has completed. [...]"

which may hint at the 'warn' option is applied only when a warning
condition is allowed to "bubble up" all the way to the top level.
(FWIW, this is how always though it worked, but it's only now I looked
into the docs and see it's ambiguous on this).


[1] https://github.com/search?q=org%3Acran+language%3Ar+R%2F+in%3Afile%2Cpath+options+warn+%22-1%22&type=Code
[2] https://github.com/wch/r-source/blob/0a31ab2d1df247a4289efca5a235dc45b511d04a/src/library/utils/R/objects.R#L402-L405
[3] https://cran.r-project.org/doc/manuals/R-lang.html#warning

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