Compilation Failure with Clang from Brewed LLVM about homebrew-core

[ZhongRuoyu]

I believe this is llvm/llvm-project#77653 (and llvm/llvm-project#84392). As a workaround, try adding the flag -L"$(brew --prefix llvm)"/lib/c++.

[talkeren]

My use case is using clang to distribute a standalone binary for mac, so I want that it will be linked against the system libc.
If anyone else is interested, this was my workaround hack for this issue: (warning: it is permentatly modifying the libc++ headers, I am just using it in a github action)

sed -i '' '/^#define _LIBCPP_HAS_NO_VENDOR_AVAILABILITY_ANNOTATIONS/d' "$(brew --prefix llvm)"/include/c++/v1/__config_site

after that I could target the minimum version MacOS version that is required for std::println:
echo "CXXFLAGS=-mmacos-version-min=13.3" >> $GITHUB_ENV

[gen740]

As a workaround, try adding the flag -L"$(brew --prefix llvm)"/lib/c++.

It works for me. Thanks!

[talkeren]

Hey, I have encountered the same issue and looked into the issue. Yes linking against the bundled libc++ solves it, but it seems that libc++ for macos does support <print> with the native lib, the this is how it was implemented:
llvm/llvm-project@4a87db6
_LIBCPP_AVAILABILITY_HAS_PRINT has to be set to zero so it will just skip using the linked functions and loss a small functionality.
And they set it only with the vendor availability annotations for apple:
https://github.com/llvm/llvm-project/blob/80f510bbc9561324fc13bac22aad2e3ef47a59c5/libcxx/cmake/caches/Apple.cmake#L9
In the libc++ includes in homebrew _LIBCPP_AVAILABILITY_HAS_PRINT is 1, so this feature is only available when linking against the bundled libc++.

[Bo98]

I guess ultimately the problem is the wrong C++ headers being used. If you're linking with system libc++ then it should be using the C++ headers shipped with the macOS SDK.

Currently there isn't an easy way to tell clang to switch between libc++ installs, unless you mess around with -nostdinc++.

Maybe splitting libc++ into a separate formula might be a starting point here.

[talkeren]

If you're linking with system libc++ then it should be using the C++ headers shipped with the macOS SDK.

clang and libc++ has the feature to target specific versions of macos (with the availability annotation), so in this situation I still wish that I could use the newest libc++ with that capability and not be stuck with the slowly updating macos sdks. Maybe a different formula for libc++ with LIBCXX_ENABLE_VENDOR_AVAILABILITY_ANNOTATIONS could be great.

[HerrCai0907]

The bug reason is clang use header files which are installed by brew but use the libc++ in sysroot.
So another workaround is remove the header files in folder of homebrew.

mv /opt/homebrew/Cellar/llvm/18.1.5/include/c++/v1 /opt/homebrew/Cellar/llvm/18.1.5/include/c++/v1.bak

[github-actions]

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