`std::uncaught_exception` error in vendored catch.h with clang++-20 and C++20 standard

[tylermorganwall]

Description

The vendored catch.h header in the testthat package references std::uncaught_exception, which has been deprecated in C++17 and removed in C++20. When compiling with clang++-20 and the -std=gnu++20 flag, this leads to a compilation error:

clang++-20 -stdlib=libc++ -std=gnu++20 -I"/opt/R/devel/lib/R/include" -DNDEBUG  -I'/github/home/R/x86_64-pc-linux-gnu-library/4.5/Rcpp/include' -I'/github/home/R/x86_64-pc-linux-gnu-library/4.5/RcppThread/include' -I'/github/home/R/x86_64-pc-linux-gnu-library/4.5/progress/include' -I'/github/home/R/x86_64-pc-linux-gnu-library/4.5/spacefillr/include' -I'/github/home/R/x86_64-pc-linux-gnu-library/4.5/testthat/include' -I/usr/local/include   -D RAY_REPRODUCE_PERLIN -DSTRICT_R_HEADERS -DRAY_HAS_X11 -DHAS_SSE -DHAS_SSE2 -DRAYSIMD -DRAYSIMDVECOFF -fpic  -O3 -Wall -pedantic -frtti -Wp,-D_FORTIFY_SOURCE=3 -Wall -pedantic  -c test-runner.cpp -o test-runner.o
  In file included from test-runner.cpp:7:
  In file included from /github/home/R/x86_64-pc-linux-gnu-library/4.5/testthat/include/testthat.h:1:
  In file included from /github/home/R/x86_64-pc-linux-gnu-library/4.5/testthat/include/testthat/testthat.h:72:
  /github/home/R/x86_64-pc-linux-gnu-library/4.5/testthat/include/testthat/vendor/catch.h:8382:20: error: no member named 'uncaught_exception' in namespace 'std'; did you mean 'uncaught_exceptions'?
   8382 |         if ( !std::uncaught_exception() ){
        |               ~~~~~^
  /usr/lib/llvm-20/bin/../include/c++/v1/__exception/operations.h:35:31: note: 'uncaught_exceptions' declared here
     35 | _LIBCPP_EXPORTED_FROM_ABI int uncaught_exceptions() _NOEXCEPT;
        |                               ^
  In file included from test-runner.cpp:7:
  In file included from /github/home/R/x86_64-pc-linux-gnu-library/4.5/testthat/include/testthat.h:1:
  In file included from /github/home/R/x86_64-pc-linux-gnu-library/4.5/testthat/include/testthat/testthat.h:72:
  /github/home/R/x86_64-pc-linux-gnu-library/4.5/testthat/include/testthat/vendor/catch.h:8705:22: error: no member named 'uncaught_exception' in namespace 'std'; did you mean 'uncaught_exceptions'?
   8705 |             if( std::uncaught_exception() )
        |                 ~~~~~^
  /usr/lib/llvm-20/bin/../include/c++/v1/__exception/operations.h:35:31: note: 'uncaught_exceptions' declared here
     35 | _LIBCPP_EXPORTED_FROM_ABI int uncaught_exceptions() _NOEXCEPT;
        |                               ^
  2 errors generated.
  make: *** [/opt/R/devel/lib/R/etc/Makeconf:204: test-runner.o] Error 1
  ERROR: compilation failed for package ‘rayrender’
  * removing ‘/tmp/Rtmp5ZqS0O/pkg-lib2ec7db28e4f/rayrender’

This issue arises in two locations in catch.h:

• Line 8382: if ( !std::uncaught_exception() ){
• Line 8705: if( std::uncaught_exception() )

This error was detected by compiling the rayrender package with the rhub clang20 runner.

https://github.com/tylermorganwall/rayrender/actions/runs/12653086666/job/35257420480

Suggested Fix

Replace the calls to std::uncaught_exception() with std::uncaught_exceptions() > 0, which is the recommended replacement in C++17 and later.

Here’s the updated code:

// ScopedMessage::~ScopedMessage
if ( std::uncaught_exceptions() == 0 ){
    getResultCapture().popScopedMessage(m_info);
}

and

// Section::~Section
if( std::uncaught_exceptions() > 0 )
    getResultCapture().sectionEndedEarly( endInfo );
else
    getResultCapture().sectionEnded( endInfo );

[tylermorganwall]

I have just received a CRAN notice that my package will be taken down unless this issue is fixed by 2025-03-05.

https://www.r-project.org/nosvn/R.check/r-devel-linux-x86_64-fedora-clang/rayrender-00install.html

[tylermorganwall]

Update for anyone else facing this issue:

I have updated my package to temporarily remove compiled tests by wrapping all calls to Catch2 functions and <testthat.h> (which includes the deprecated C++20 function) in a preprocessor guard.

#ifdef NOT_CRAN
#include <testthat.h>
#include <Rcpp.h>

context("...") {
  ...
}
#endif

However, because testthat includes the following dummy function to ensure the symbol is registered:

# This dummy function definition is included with the package to ensure that
# 'tools::package_native_routine_registration_skeleton()' generates the required
# registration info for the 'run_testthat_tests' symbol.
(function() {
  .Call("run_testthat_tests", FALSE, PACKAGE = "rayrender")
})

I had failures due to it trying to I needed to resolve the run_testthat_tests symbol, which it couldn't because I had to add a guard to test-runner.cpp to prevent it from including <testthat.h> (which contains the symbol R was looking for). So I had to also include a dummy function so that that symbol would resolve as well.

/*
 * Please do not edit this file -- it ensures that your package will export a
 * 'run_testthat_tests()' C routine that can be used to run the Catch unit tests
 * available in your package.
 */
#ifdef NOT_CRAN
#define TESTTHAT_TEST_RUNNER
#include <testthat.h>
#else 

#include <R.h>
#include <Rinternals.h>
extern "C" SEXP run_testthat_tests(SEXP use_xml_sxp) {
  return Rf_ScalarLogical(true);
}
#endif