Summary

clang-tidy 21.1.2 from Homebrew (llvm@21, arm64) segfaults when analyzing JUCE-heavy translation units in the GhostLathe audio plugin project. The crash is deterministic on macOS 14.5 when running against GhostLatheProcessor.cpp or the associated unit tests.

Version

21.1.2 (Homebrew llvm@21 build, arm64)

OS

macOS 14.5 (arm64)

Steps to Reproduce

1. Install llvm@21 via Homebrew: brew install llvm@21.
2. Configure GhostLathe with compile commands:

   cmake -S . -B build -G Ninja \ -DCMAKE_BUILD_TYPE=Debug \ -DCMAKE_EXPORT_COMPILE_COMMANDS=ON 

3. Ensure /opt/homebrew/opt/llvm@21/bin is first on PATH.
4. Run clang-tidy against the problematic TU:

   run-clang-tidy -p build \ -clang-tidy-binary clang-tidy \ src/plugin/GhostLatheProcessor.cpp 

Expected Behavior

clang-tidy completes analysis and emits diagnostics for the translation unit.

Actual Behavior

clang-tidy terminates with a segmentation fault while traversing JUCE-generated constructs in GhostLatheProcessor.cpp. The crash reproduces consistently on related unit tests (tests/plugin/GhostLatheProcessorTests.cpp) as well. A sanitized backtrace and logs are included in the attachments.

Additional Context

• Downgrading to llvm@20 (clang-tidy 20.1.x) avoids the crash; we currently pin CI to that toolchain.
• JUCE version: 8.0.10. Project builds with CMake 3.30.2 and Ninja 1.12.1; SDKROOT points to the Xcode 16 macOS 14.4/26.0 SDK.
• Sanitized reproduction bundle (sources subset, compile commands, logs) plus stack trace are published here: https://gist.github.com/DavidDanielSauce/e5cea023e78b31b9b0de0572ed7fef1f.
  • The gist contains clang_tidy_crash_report.md, clang_tidy_crash_20250930.log, and a base64-encoded clang_tidy_crash_bundled.tgz (decode with base64 -d clang_tidy_crash_bundled.tgz.base64 > clang_tidy_crash_bundled.tgz).
• Happy to provide additional sanitized artefacts (e.g., full compile database) if needed.

Thanks for taking a look!