[R-pkg-devel] How to update "SystemRequirements: C++11"?

[Iñaki Ucar]

On Mon, 6 Feb 2023 at 23:27, Avraham Adler <avraham.adler using gmail.com> wrote:
>
> On Mon, Feb 6, 2023 at 9:46 PM Duncan Murdoch <murdoch.duncan using gmail.com> wrote:
> >
> > On 06/02/2023 4:01 p.m., Duncan Murdoch wrote:
> > > On 06/02/2023 3:46 p.m., Winston Chang wrote:
> > >> I recently submitted a package to CRAN with "SystemRequirements: C++11".
> > >> This raises the following NOTE on R-devel, and I was asked to fix and
> > >> resubmit:
> > >>
> > >> * checking C++ specification ... NOTE
> > >>     Specified C++11: please update to current default of C++17
> > >>
> > >> If I understand correctly, I have two options, neither of which will work:
> > >> 1. Remove "SystemRequirements: C++11" entirely. The problem with this is
> > >> that on systems with older versions of R (3.6 and below, I believe), it may
> > >> try to compile the package with an older C++ standard, which will fail.
> > >> 2. Update it to "SystemRequirements: C++17". The problem here is that on
> > >> systems that don't have a C++17 compiler, the package won't build -- even
> > >> though the package only actually requires a C++11 compiler.
> > >>
> > >> How should I deal with this?
> > >
> > > Are you allowed to say "C++11 or C++17"?
> >
> > Actually I can partially answer this:  the test is not based on
> > SystemRequirements, but on the log of the build, which now contains
> > lines like this:
> >
> >    using C compiler: ‘Apple clang version 12.0.0 (clang-1200.0.32.28)’
> >    using C++ compiler: ‘Apple clang version 12.0.0 (clang-1200.0.32.28)’
> >    using C++11
> >    using SDK: ‘MacOSX11.1.sdk’
> >
> > I get "using C++11" because of this line in Makevars:
> >
> >    CXX_STD = CXX11
> >
> > So I guess the answer is to change your Makevars to make that line
> > conditional on running under an old version of R.  If you figure out how
> > to do that, could you post the recipe here?
>
> I believe this is closely related to this email [1]. Dirk and I and
> Aymeric have been going through the same issue with nloptr as well.
> Our current opinion is to leave it out, as it would restrict more
> users to demand C++17, which is unneeded, than to have users with over
> a decade old compiler which does not have C++11. Dirk and Aymeric,
> please chime in if I have misstated. Regardless, according to
> Professor Ripley, if you require specific features, you should mark
> them in _both_ Makevars and SystemRequirements, which is implied in
> the "r-devel" version of WRE which adds the words "also" in section
> 1.2.4.

Could you please point to the specific passage? According to [1],
section 1.2.4, declaring the C++ standard in SystemRequirements is
only mandatory for C++17 or later.

[1] https://cran.r-project.org/doc/manuals/r-devel/R-exts.html#Using-C_002b_002b-code

-- 
Iñaki Úcar