[Rd] Change to r-devel warns on #pragma

[Mark van der Loo]

Hi Patrick,

It was recently added as a cran policy (thanks Dirk's cran policy watch:
https://twitter.com/markvdloo/status/935810241190617088).

It seems to be a general stricter policy on keeping to the C(++) standard.
Warnings are there for a reason and should usually not be ignored. I'm not
familiar with the warning you are suppressing  but it seems likely that
your code might assume type size that is not guaranteed by the standard and
thus may differ a cross systems/compilers. (An example is wchar_t which has
typically 16b on Windows as guaranteed by the standard and 32b on Unix)

Best,
Mark

On Mon, Dec 11, 2017, 4:33 PM Patrick Perry <pperry at stern.nyu.edu> wrote:

> A recent change to r-devel causes an R CMD check warning when a C file
> includes a "#pragma GCC diagnostic ignored" pragma:
>
> https://github.com/wch/r-source/commit/b76c8fd355a0f5b23d42aaf44a879cac0fc31fa4
> . This causes the CRAN checks for the "corpus" package to emit a
> warning:
>
> https://www.r-project.org/nosvn/R.check/r-devel-linux-x86_64-fedora-clang/corpus-00check.html
> .
>
> The offending code is in an upstream library bundled with the package:
> https://github.com/patperry/corpus/blob/master/src/table.c#L118
>
> #pragma GCC diagnostic push
> #pragma GCC diagnostic ignored "-Wtype-limits"
>          // gcc emits a warning if sizeof(size_t) > sizeof(unsigned)
>
>          if ((size_t)size > SIZE_MAX / sizeof(*items)) {
> #pragma GCC diagnostic pop
>
> This is code appears in the "corpus" library that gets bundled with the
> corpus r-package but can also be installed by itself. I am the
> maintainer for both projects but in theory the library is independent
> from the r package (the latter depends on the former). I put the pragma
> there in the first place because this is the cleanest way I know of to
> remove the gcc compiler warning "comparison is always false due to
> limited range of data type" which appears whenever sizeof(unsigned) <
> sizeof(size_t); the warning does not appear for clang.
>
> Does anyone have recommendations for what I should do to remove the R
> CMD check warning? Is it possible to do this while simultaneously
> removing the gcc warning? Note that the package does not use autoconf.
>
> Fortunately, I am the maintainer for the included library, so I can
> potentially remove the pragma. However, I can imagine that there are
> many other cases of R packages bundling C libraries where R package
> maintainers do not have control over the downstream source. Perhaps
> there is a compelling case for this new CRAN check that I'm not seeing,
> but it seems to me that this additional CRAN check will cause extra work
> for package developers without providing any additional safety for R
> users. Package developers that do not control bundled upstream libraries
> will have to resort to `sed s/^#pragma.*//` or manually patch unfamiliar
> code to remove the CRAN warning, potentially introducing bugs in the
> process.
>
>
> Patrick
>
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