OSx: 'uncaught_exceptions' has been explicitly marked unavailable

[tdegeus]

Describe the bug
On macOS we're getting:

[91/110] Building CXX object src/CMakeFiles/Catch2.dir/catch2/internal/catch_uncaught_exceptions.cpp.o
FAILED: src/CMakeFiles/Catch2.dir/catch2/internal/catch_uncaught_exceptions.cpp.o 
$BUILD_PREFIX/bin/x86_64-apple-darwin13.4.0-clang++  -I$SRC_DIR/src/catch2/.. -I$SRC_DIR/build/generated-includes -march=core2 -mtune=haswell -mssse3 -ftree-vectorize -fPIC -fPIE -fstack-protector-strong -O2 -pipe -stdlib=libc++ -fvisibility-inlines-hidden -fmessage-length=0 -isystem $PREFIX/include -fdebug-prefix-map=$SRC_DIR=/usr/local/src/conda/catch2-3.5.0 -fdebug-prefix-map=$PREFIX=/usr/local/src/conda-prefix -O3 -DNDEBUG -isysroot /Applications/Xcode_13.2.1.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.9.sdk -mmacosx-version-min=10.9 -ffile-prefix-map=$SRC_DIR/= -MD -MT src/CMakeFiles/Catch2.dir/catch2/internal/catch_uncaught_exceptions.cpp.o -MF src/CMakeFiles/Catch2.dir/catch2/internal/catch_uncaught_exceptions.cpp.o.d -o src/CMakeFiles/Catch2.dir/catch2/internal/catch_uncaught_exceptions.cpp.o -c $SRC_DIR/src/catch2/internal/catch_uncaught_exceptions.cpp
$SRC_DIR/src/catch2/internal/catch_uncaught_exceptions.cpp:21:21: error: 'uncaught_exceptions' is unavailable: introduced in macOS 10.12 - see https://conda-forge.org/docs/maintainer/knowledge_base.html#newer-c-features-with-old-sdk
        return std::uncaught_exceptions() > 0;
                    ^
$BUILD_PREFIX/bin/../include/c++/v1/exception:185:63: note: 'uncaught_exceptions' has been explicitly marked unavailable here
_LIBCPP_FUNC_VIS _LIBCPP_AVAILABILITY_UNCAUGHT_EXCEPTIONS int uncaught_exceptions() _NOEXCEPT;
                                                              ^
1 error generated.

See conda-forge/catch2-feedstock#58

It could be that #1911 is not properly detected?

Expected behavior
Proper build and run.

Reproduction steps
https://github.com/conda-forge/catch2-feedstock/blob/main/recipe/meta.yaml
https://github.com/conda-forge/catch2-feedstock/blob/main/recipe/build.sh
https://github.com/conda-forge/catch2-feedstock/blob/main/recipe/run_test.sh

Platform information:

• OS: macOS
• Compiler+version: clang 16
• Catch version: 3.5.0

Additional context

[horenmar]

It could be that #1911 is not properly detected?

No. If it was not properly detected, the error would not be happening.

---

I don't have expertise with either Conda or MacOS packaging, but after talking with some people who do, here is what I think is happening

• Conda targets ancient version of MacOS during compilation. 10.09 was released 2013 and the support ended in 2016.
• Apple Clang checks whether specific features are available on the target version of MacOS and errors out if not. However, Clang assumes that it targets the system libc++. Conda builds and distributes its own libc++, but Clang does not know that.
• The actual libc++ defines the feature availability macro to the correct value, and Catch2 tries using std::uncaught_exceptions.
• Clang sees that, and because the system libc++ for MacOS 10.09 does not support std::uncaught_exceptions, it errors out.

The solution is to

1. Define _LIBCPP_DISABLE_AVAILABILITY during compilation.
2. Stop targetting ancient versions of MacOS.