Build fails on macOS Apple Silicon (aarch64) with "a 'libclang' shared library is not loaded on this thread"

[youngqj]

Environment

• OS: macOS Sonoma 24.5.0 (Apple Silicon, aarch64-apple-darwin)
• rustc: rustc 1.88.0 (6b00bc388 2025-06-23)
• OpenCV: 4.11.0 (Installed via Homebrew)
• LLVM: 19.1.0 (Installed via Homebrew)
• Xcode Command Line Tools: Installed and up-to-date

Problem Description

When building a project with opencv-rs as a dependency on an Apple Silicon Mac, the build consistently fails during the opencv crate's build script execution.

The error message is:
thread 'main' panicked at /Users/yangqijun/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/clang-sys-1.8.1/src/lib.rs:1859:1: a 'libclang' shared library is not loaded on this thread

This happens even though pkg-config successfully finds the OpenCV library, and all relevant environment variables seem to be set correctly. The issue appears to be with clang-sys's ability to dynamically load libclang.dylib at runtime within the build script.

Cargo.toml Dependency

[dependencies]
opencv = "0.92"

Attempts to fix

We have tried multiple combinations of environment variables, including all standard and community-suggested solutions, but the error persists.

Attempt 1: Basic Paths

export LIBCLANG_PATH="/opt/homebrew/opt/llvm/lib"
export PKG_CONFIG_PATH="/opt/homebrew/opt/opencv/lib/pkgconfig"
cargo build

Result: Failed with the same error.

Attempt 2: Comprehensive Standard Paths

export PKG_CONFIG_PATH="/opt/homebrew/opt/opencv/lib/pkgconfig"
export LIBCLANG_PATH="/opt/homebrew/opt/llvm/lib"
export DYLD_FALLBACK_LIBRARY_PATH="$(xcode-select -p)/Toolchains/XcodeDefault.xctoolchain/usr/lib"
export LD_LIBRARY_PATH="/opt/homebrew/lib"
export PATH="/opt/homebrew/opt/llvm/bin:$PATH"
cargo build

Result: Failed with the same error.

Attempt 3: Adding BINDGEN_EXTRA_CLANG_ARGS (based on community suggestions)

export PKG_CONFIG_PATH="/opt/homebrew/opt/opencv/lib/pkgconfig"
export LIBCLANG_PATH="/opt/homebrew/opt/llvm/lib"
export LD_LIBRARY_PATH="/opt/homebrew/lib"
export PATH="/opt/homebrew/opt/llvm/bin:$PATH"
export BINDGEN_EXTRA_CLANG_ARGS="-isysroot $(xcrun --sdk macosx --show-sdk-path)"
cargo build

Result: Still failed with the exact same error.

Final Build Log

This is the output from the last attempt (Attempt 3).

=== Crate version: Some("0.92.3")
=== Environment configuration:
===   OpenCV_DIR = Some("/opt/homebrew/opt/opencv")
===   PKG_CONFIG_PATH = Some("/opt/homebrew/opt/opencv/lib/pkgconfig")
...
=== Probing OpenCV library using pkg_config
=== Successfully probed using: pkg_config
=== OpenCV library configuration: Library {
    include_paths: [
        "/opt/homebrew/opt/opencv/include/opencv4",
    ],
    version: Version {
        major: 4,
        minor: 11,
        patch: 0,
    },
...
}
=== Detected OpenCV module header dir at: /opt/homebrew/opt/opencv/include/opencv4/opencv2
=== Found OpenCV version: 4.11.0 in headers located at: /opt/homebrew/opt/opencv/include/opencv4
=== Generating code in: /path/to/project/src-tauri/target/debug/build/opencv-621a83dcc0ce5751/out
=== Placing generated bindings into: /path/to/project/src-tauri/target/debug/build/opencv-621a83dcc0ce5751/out/opencv
=== Using OpenCV headers from: /opt/homebrew/opt/opencv/include/opencv4

thread 'main' panicked at /Users/yangqijun/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/clang-sys-1.8.1/src/lib.rs:1859:1:
a `libclang` shared library is not loaded on this thread
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

Question

Given that all standard environment variable configurations have been attempted, could this be a deeper issue related to System Integrity Protection (SIP), the dynamic linker (dyld), or a specific incompatibility between clang-sys, the Homebrew-installed llvm, and the Apple Silicon architecture?

Are there any other diagnostic steps or environment configurations we can try to resolve this dynamic loading failure?

Thank you for your help.

[youngqj]

最终的成功方案是一个组合拳，结合了社区智慧和版本升级：

1. 启用 clang-runtime 特性: 这是最关键的一步。通过研究 GitHub Issue #657，我们发现在 Cargo.toml 中为 opencv 依赖启用 clang-runtime 特性，可以强制 clang-sys 在运行时查找 libclang.dylib，解决了动态加载失败的问题。

2. 升级 opencv 版本: 启用 clang-runtime 后，虽然解决了环境问题，但出现了大量关于 Vector 和 trait 实现的编译错误。这通常是由于库版本不匹配或内部API变更导致的。我们将 opencv 版本从 0.92.3 升级到了 0.94.2，成功解决了这些代码兼容性问题。

最终 Cargo.toml 配置:

[dependencies]
# ... 其他依赖

# OpenCV 支持 (需要系统库)
opencv = { version = "0.94.2", default-features = false, features = ["imgproc", "imgcodecs", "videoio", "highgui", "clang-runtime"] }

3. macOS 正确编译方法 (终极版)

要在 macOS (特别是 Apple Silicon) 环境下成功编译本项目，请严格遵循以下步骤：

前提: 确保已通过 Homebrew 安装了必要的库。

brew install opencv llvm

编译命令: 在项目根目录的 src-tauri 文件夹下，执行以下单行命令。它会设置所有必要的环境变量并开始构建。

export PKG_CONFIG_PATH="/opt/homebrew/opt/opencv/lib/pkgconfig" && \
export LIBCLANG_PATH="/opt/homebrew/opt/llvm/lib" && \
export LD_LIBRARY_PATH="/opt/homebrew/lib" && \
export PATH="/opt/homebrew/opt/llvm/bin:$PATH" && \
export BINDGEN_EXTRA_CLANG_ARGS="-isysroot $(xcrun --sdk macosx --show-sdk-path)" && \
cargo build

4. 结论

本次问题的成功解决，再次印证了项目“以交付为导向”的原则。在遇到顽固的环境问题时，积极从社区寻求解决方案，并结合版本升级策略，最终高效地解决了问题，使项目重回正轨。

[twistedfall]

Did you check https://github.com/twistedfall/opencv-rust/blob/master/TROUBLESHOOTING.md, item 8?