通过 Homebrew 安装 ccl 会输出与 libffi 和 llvm 相关的警告消息

问题描述

我正在尝试设置我的 neovim C++ 开发环境，并且想使用 ccls 作为我的 coc 语言服务器。

当我使用 ccls 安装 Homebrew 时，它会安装 libffi 和 llvm 作为依赖项。好像ccls安装成功了，但是好像我需要配置PATH变量，LDFLAGS和CPPFLAGS。

但我不知道 libffi 和 llvm 是做什么用的，它们建议使用不同的 LDFLAGS 和 CPPFLAGS，这很令人困惑。

不导出任何变量来使用ccls可以吗？或者，我应该在 ~/.zshrc 中导出哪个版本？

以下是我对 brew install ccls 的控制台输出。

❯ brew install ccls
==> Downloading https://homebrew.bintray.com/bottles/libffi-3.3.big_sur.bottle.tar.gz
######################################################################## 100.0%
==> Downloading https://homebrew.bintray.com/bottles/llvm-11.0.0_1.big_sur.bottle.tar.gz
==> Downloading from https://d29vzk4ow07wi7.cloudfront.net/c8e30903a9a4f695780e1eeeaa2cf4d5a95141a1cac98ab1bbc811817cde39ca?response-content-disposition=attachment%3Bfilename%3D
######################################################################## 100.0%
==> Downloading https://homebrew.bintray.com/bottles/ccls-0.20201219.big_sur.bottle.tar.gz
==> Downloading from https://d29vzk4ow07wi7.cloudfront.net/934fb8fd594d6e7adbfa14b5608f1de14309db34f2cf61a0cb572bdc772b2aa3?response-content-disposition=attachment%3Bfilename%3D
######################################################################## 100.0%
==> Installing dependencies for ccls: libffi and llvm
==> Installing ccls dependency: libffi
==> Pouring libffi-3.3.big_sur.bottle.tar.gz
==> Caveats
libffi is keg-only,which means it was not symlinked into /usr/local,because macOS already provides this software and installing another version in
parallel can cause all kinds of trouble.

For compilers to find libffi you may need to set:
  export LDFLAGS="-L/usr/local/opt/libffi/lib"
  export CPPFLAGS="-I/usr/local/opt/libffi/include"

==> Summary
?  /usr/local/Cellar/libffi/3.3: 17 files,540.2KB
==> Installing ccls dependency: llvm
==> Pouring llvm-11.0.0_1.big_sur.bottle.tar.gz
==> Caveats
To use the bundled libc++ please add the following LDFLAGS:
  LDFLAGS="-L/usr/local/opt/llvm/lib -Wl,-rpath,/usr/local/opt/llvm/lib"

llvm is keg-only,because macOS already provides this software and installing another version in
parallel can cause all kinds of trouble.

If you need to have llvm first in your PATH run:
  echo 'export PATH="/usr/local/opt/llvm/bin:$PATH"' >> ~/.zshrc

For compilers to find llvm you may need to set:
  export LDFLAGS="-L/usr/local/opt/llvm/lib"
  export CPPFLAGS="-I/usr/local/opt/llvm/include"

==> Summary
?  /usr/local/Cellar/llvm/11.0.0_1: 8,922 files,1.4GB
==> Installing ccls
==> Pouring ccls-0.20201219.big_sur.bottle.tar.gz
?  /usr/local/Cellar/ccls/0.20201219: 5 files,1.5MB
==> Caveats
==> libffi
libffi is keg-only,because macOS already provides this software and installing another version in
parallel can cause all kinds of trouble.

For compilers to find libffi you may need to set:
  export LDFLAGS="-L/usr/local/opt/libffi/lib"
  export CPPFLAGS="-I/usr/local/opt/libffi/include"

==> llvm
To use the bundled libc++ please add the following LDFLAGS:
  LDFLAGS="-L/usr/local/opt/llvm/lib -Wl,because macOS already provides this software and installing another version in
parallel can cause all kinds of trouble.

If you need to have llvm first in your PATH run:
  echo 'export PATH="/usr/local/opt/llvm/bin:$PATH"' >> ~/.zshrc

For compilers to find llvm you may need to set:
  export LDFLAGS="-L/usr/local/opt/llvm/lib"
  export CPPFLAGS="-I/usr/local/opt/llvm/include"

解决方法

libffi 只是一个库。 llvm 是一个编译器基础架构。 libc++ 是 LLVM 项目 的 C++ 标准库。您可以使用 LLVM 库或 GNU (libstdc++) 库。这取决于您的软件项目（或您的个人偏好）您使用什么库。

由于 macOS 已经提供了 llvm 安装，您可以可选切换到由 brew 安装为依赖项的安装 - 这不是必需的。

LDFLAGS 环境变量确实包含由编译器（gcc/g++ 或 clang/clang++）传递给链接器的附加标志，即添加链接器可以找到库对象的路径然后，如果需要/使用，这些文件将链接到您的二进制文件。

和 CPPFLAGS 做同样的事情，但这次标志直接针对编译器，即为库的头文件添加额外的搜索路径。

在您的情况下，您不必从 .zshrc 导出任何（附加）变量，ccls 无需定义这些变量即可正常工作。

c++language-server-protocol libffi llvm neovim