Clangd in Nix

I’ve been using Nix a lot recently since it handles dependency management very cleanly, but one gripe that I’ve been having is that when I’m doing C/C++ development work using nix develop, all my dependencies are actually in the Nix store in /nix, so my clangd editor plugin won’t be able to find them.

Fortunately, clangd supports looking for a file called compile_commands.json, which describes the compilation commands used for each file, with absolute paths for all dependencies.

For CMake-based projects, there’s an option to dump this information automatically into the build directory, which I typically then symlink into my project’s root directory for my editor to find and apply to my files. Here’s the snippet:

# Generate the `compile_commands.json` file.
set(CMAKE_EXPORT_COMPILE_COMMANDS ON CACHE INTERNAL "")

if(CMAKE_EXPORT_COMPILE_COMMANDS)
  set(CMAKE_CXX_STANDARD_INCLUDE_DIRECTORIES
    ${CMAKE_CXX_IMPLICIT_INCLUDE_DIRECTORIES})
endif()