Compilation Failure with Clang from Brewed LLVM

[gen740]

brew gist-logs <formula> link OR brew config AND brew doctor output

$ brew config
HOMEBREW_VERSION: 4.2.19
ORIGIN: https://github.com/Homebrew/brew
HEAD: 54bea636b41f7953c01a7da5f488f08c1b42ffd1
Last commit: 31 hours ago
Core tap JSON: 23 Apr 03:12 UTC
Core cask tap JSON: 23 Apr 03:12 UTC
HOMEBREW_PREFIX: /opt/homebrew
HOMEBREW_CASK_OPTS: []
HOMEBREW_DISPLAY: /private/tmp/com.apple.launchd.KuCi5a7okU/org.xquartz:0
HOMEBREW_EDITOR: nvim
HOMEBREW_MAKE_JOBS: 14
Homebrew Ruby: 3.1.4 => /opt/homebrew/Library/Homebrew/vendor/portable-ruby/3.1.4/bin/ruby
CPU: 14-core 64-bit arm_palma
Clang: 15.0.0 build 1500
Git: 2.44.0 => /opt/homebrew/bin/git
Curl: 8.4.0 => /usr/bin/curl
macOS: 14.4.1-arm64
CLT: 15.3.0.0.1.1708646388
Xcode: 15.3
Rosetta 2: false

$ brew doctor
Your system is ready to brew.

Verification

• My brew doctor output says Your system is ready to brew. and am still able to reproduce my issue.
• I ran brew update and am still able to reproduce my issue.
• I have resolved all warnings from brew doctor and that did not fix my problem.
• I searched for recent similar issues at https://github.com/Homebrew/homebrew-core/issues?q=is%3Aissue and found no duplicates.

What were you trying to do (and why)?

Compile following simple C++ code with clang++.

#include <print>
int main() { std::println("{}", "Hello, World"); }

with /opt/homebrew/opt/llvm/bin/clang++ -std=c++23 test.cc.

What happened (include all command output)?

Undefined symbols for architecture arm64:
"std::__1::__is_posix_terminal(__sFILE*)", referenced from:
std::__1::__print::__is_terminalabi:ne180100 in test-285f15.o
ld: symbol(s) not found for architecture arm64
clang++: error: linker command failed with exit code 1 (use -v to see invocation)

What did you expect to happen?

Compilation successful.
I confirmed that this code builds successfully with llvm@17.

Step-by-step reproduction instructions (by running brew commands)

brew install llvm
echo '#include <print>\nint main() { std::println("{}", "Hello, World"); }' > test.cc
/opt/homebrew/opt/llvm/bin/clang++ -std=c++23 test.cc

[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++.

[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.

[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