[ffigen] Clang/Xcode visionOS issues

[dcharkes]

[SEVERE] : Header ./src/my_plugin.h: Total errors/warnings: 13.
[SEVERE] :     /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/malloc/_malloc_type.h:48:1: warning: unknown platform 'xros' in availability macro [Semantic Issue]

The origin:

+__attribute__((availability(xros, unavailable))) // visionos-warning {{unknown platform 'xros' in availability macro}}
+void xros_unavail(); // visionos-note {{}}

https://www.mail-archive.com/cfe-commits@lists.llvm.org/msg414442.html

I'm not entirely sure why we are seeing this though.

@liamappelbe have you seen this before?

[liamappelbe]

No, I haven't seen it before. Probably because I haven't updated xcode since visionos was released. Guess: could be a mismatch between your header version and your clang version?

[liamappelbe]

I just ran into this. I think the issue is that we're using clang installed from brew, which lags behind the version we get in xcode. Then when we parse headers that come from xcode, they contain this attribute that doesn't exist in the brew version yet.

I fixed it by just doing brew uninstall llvm:

liama-macbookpro:ffigen liama$ which clang
/usr/local/opt/llvm/bin/clang
liama-macbookpro:ffigen liama$ brew uninstall llvm
Uninstalling /usr/local/Cellar/llvm/16.0.6... (6,764 files, 1.6GB)
liama-macbookpro:ffigen liama$ which clang
/usr/bin/clang

I think the clang in /usr/bin is installed when we install the Xcode command line tools, xcode-select --install.

So I think we just need to remove that brew install llvm instruction from the readme.

[dcharkes]

Thanks @liamappelbe!

Works for me!

I think the clang in /usr/bin is installed when we install the Xcode command line tools, xcode-select --install.

Okay, my machine is probably in the same state as yours.
If anyone runs into issues we can update the documentation.