[R-SIG-Mac] configure tests for OpenMP fail when building CRAN binary packages

[Simon Urbanek]

Ivan, thanks, now fixed (yes, the new VMs didn't have omp.h automatically since it is not part of recipes). Please make sure you re-install any such packages directly, e.g.

install.packages("data.table",repos="https://mac.r-project.org")

since update.packages() will not see the updated binaries.

Cheers,
Simon


> On 30/12/2025, at 11:09, Ivan Krylov via R-SIG-Mac <r-sig-mac using r-project.org> wrote:
> 
> Hello,
> 
> Some packages that use a configure test for OpenMP support now don't
> detect it when being compiled for macOS:
> 
> https://www.r-project.org/nosvn/R.check/r-release-macos-arm64/RcppArmadillo-00install.html
> https://www.r-project.org/nosvn/R.check/r-release-macos-x86_64/data.table-00install.html
> 
> The test for working OpenMP support used by these two packages is
> 
> PKG_CFLAGS='-Xclang -fopenmp' PKG_LIBS=-lomp R CMD SHLIB test.c
> 
> ...completing with an exit status of 0. (Where test.c contains some
> valid OpenMP directives.) It's not ideal, but it's prone to false
> positives, not false negatives.
> 
> The problem does not happen on the macOS builder.
> 
> Could the CRAN builder be possibly missing some configuration
> pertaining to libomp.dylib? Is there anything I could do to help
> diagnose the problem?
> 
> -- 
> Best regards,
> Ivan
> 
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