在Ubuntu编译libc++遇类型特性相关错误，请求技术支援

在Ubuntu机器上按照libc++官方文档的默认编译步骤操作，编译过程中出现一系列类型特性相关的编译错误，具体错误信息如下：

from ~/projects/libcxx/llvm-project/libcxxabi/src/stdlib_exception.cpp:9:
~/projects/libcxx/llvm-project/build/include/c++/v1/__type_traits/is_trivially_destructible.h:36:4: error: #error is_trivially_destructible is not implemented
   36 | #  error is_trivially_destructible is not implemented
      |    ^~~~~
In file included from ~/projects/libcxx/llvm-project/build/include/c++/v1/new:95,
                 from ~/projects/libcxx/llvm-project/libcxxabi/src/stdlib_exception.cpp:9:
~/projects/libcxx/llvm-project/build/include/c++/v1/__type_traits/is_same.h:22:53: error: there are no arguments to ‘__is_same’ that depend on a template parameter, so a declaration of ‘__is_same’ must be available [-fpermissive]
   22 | struct _LIBCPP_TEMPLATE_VIS is_same : _BoolConstant<__is_same(_Tp, _Up)> {};
      |                                                     ^~~~~~~~~
~/projects/libcxx/llvm-project/build/include/c++/v1/__type_traits/is_same.h:22:53: note: (if you use ‘-fpermissive’, G++ will accept your code, but allowing the use of an undeclared name is deprecated)
~/projects/libcxx/llvm-project/build/include/c++/v1/__type_traits/is_same.h:22:72: error: template argument 1 is invalid
   22 | struct _LIBCPP_TEMPLATE_VIS is_same : _BoolConstant<__is_same(_Tp, _Up)> {};
      |                                                                        ^
~/projects/libcxx/llvm-project/build/include/c++/v1/__type_traits/is_same.h:26:48: error: expected primary-expression before ‘,’ token
   26 | inline constexpr bool is_same_v = __is_same(_Tp, _Up);
      |                                                ^
~/projects/libcxx/llvm-project/build/include/c++/v1/__type_traits/is_same.h:26:53: error: expected primary-expression before ‘)’ token
   26 | inline constexpr bool is_same_v = __is_same(_Tp, _Up);

解决方法 #

1. 升级编译器版本 #

这类错误大多因使用的GCC版本过低，不支持libc++依赖的内置类型特性函数（如__is_same、__is_trivially_destructible）。Ubuntu系统可通过以下命令升级到符合要求的GCC版本：

sudo apt update
sudo apt install gcc-10 g++-10
sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-10 100
sudo update-alternatives --install /usr/bin/g++ g++ /usr/bin/g++-10 100

2. 显式指定编译器重新配置CMake #

进入构建目录，清理原有配置后，指定升级后的编译器重新生成构建文件：

cd ~/projects/libcxx/llvm-project/build
rm -rf ./*
cmake -G Ninja ../llvm \
  -DCMAKE_C_COMPILER=gcc-10 \
  -DCMAKE_CXX_COMPILER=g++-10 \
  -DLLVM_ENABLE_PROJECTS="libcxx;libcxxabi"

3. 确保LLVM仓库完整 #

检查并补全llvm-project的子模块，避免因文件缺失导致编译错误：

cd ~/projects/libcxx/llvm-project
git submodule update --init --recursive

4. 切换到Clang编译器编译 #

libc++原生适配Clang，使用Clang可规避多数GCC兼容性问题。先安装Clang：

sudo apt install clang-14 lldb-14 lld-14
sudo update-alternatives --install /usr/bin/clang clang /usr/bin/clang-14 100
sudo update-alternatives --install /usr/bin/clang++ clang++ /usr/bin/clang++-14 100

再重新配置CMake：

cd ~/projects/libcxx/llvm-project/build
rm -rf ./*
cmake -G Ninja ../llvm \
  -DCMAKE_C_COMPILER=clang \
  -DCMAKE_CXX_COMPILER=clang++ \
  -DLLVM_ENABLE_PROJECTS="libcxx;libcxxabi"

内容的提问来源于stack exchange，提问作者DDG