clang-tidy broken with llvm v19.1.3

[lukeshingles]

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

https://gist.github.com/lukeshingles/b1477f4b5eaf327af99940ec848213b4

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)?

clang-tidy is no longer finding system headers since the llvm 19.1.3 update (#196094)

What happened (include all command output)?

$ clang-tidy helloworld.cpp
4 warnings and 1 error generated.
Error while processing /Users/luke/test/helloworld.cpp.
warning: -lunwind: 'linker' input unused [clang-diagnostic-unused-command-line-argument]
warning: argument unused during compilation: '-L/opt/homebrew/opt/llvm/lib' [clang-diagnostic-unused-command-line-argument]
warning: argument unused during compilation: '-L/opt/homebrew/opt/llvm/lib/c++' [clang-diagnostic-unused-command-line-argument]
warning: argument unused during compilation: '-L/opt/homebrew/opt/llvm/lib/unwind' [clang-diagnostic-unused-command-line-argument]
helloworld.cpp:1:10: error: 'iostream' file not found [clang-diagnostic-error]
    1 | #include <iostream>
      |          ^~~~~~~~~~
Found compiler error(s).

What did you expect to happen?

Using llvm 19.1.2 formula, the output is:

$ clang-tidy helloworld.cpp
4 warnings generated.
warning: -lunwind: 'linker' input unused [clang-diagnostic-unused-command-line-argument]
warning: argument unused during compilation: '-L/opt/homebrew/opt/llvm/lib' [clang-diagnostic-unused-command-line-argument]
warning: argument unused during compilation: '-L/opt/homebrew/opt/llvm/lib/c++' [clang-diagnostic-unused-command-line-argument]
warning: argument unused during compilation: '-L/opt/homebrew/opt/llvm/lib/unwind' [clang-diagnostic-unused-command-line-argument]

(Some warnings but no error finding <iostream>).

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

// helloworld.cpp
#include <iostream>

int main() {
  std::cout << "Hello World!";
  return 0;
}

pip install compiledb
compiledb make helloworld
clang-tidy helloworld.cpp

[lukeshingles]

I get the same errors when I run clang-tidy from pip (latest version is 19.1.0) when brew llvm 19.1.3 is installed.

[carlocab]

Oh, that's annoying. Looks like clang-tidy does not use Clang config files.

As a workaround, try

xcrun clang-tidy helloworld.cpp

[Congyuwang]

Similar problem, but with clang. With 19.1.3, clang can't find stuff like #include<string>.

Now I'll have to manually add --sysroot=/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk for things to work.

I wonder if this is as expected. Or what is the right way to fix this system-header-missing problem?

[lukeshingles]

For me, I didn’t have any problem compiling with clang++. Does my simple example compile?

[Congyuwang]

I am compiling with a rust-c++ program. Simple examples like this certainly won't have any problem. But I think it is quite improper to make such a potential breaking change, without any major versioning. Moreover, now you can brew install llvm@19 but not [email protected]. So there isn't even a simple way to rollback.

[carlocab]

@Congyuwang, I can't reproduce your issue so I'll need to know:

• the output of your brew config
• the output of your brew doctor
• the output of ls -la /Library/Developer/CommandLineTools
• the exact steps needed to reproduce the failure you're seeing