[Asooka]

You make your build system emit a compile-definitions.json file that has all the compiler flags for every file you compile and feed it to a language server (rtags or clangd usually, either standalone or part of another plugin like YouCompleteMe). CMake has a flag to do that as part of its configuration step (and remembers it), for other build systems you can use something like bear: https://github.com/rizsotto/Bear .

[samus]

For future reference, as I found this information to be difficult to find: the flag for CMake is `CMAKE_EXPORT_COMPILE_COMMANDS=YES`. In out-of-source builds, the output file will be in the build directory, therefore one has to create a symlink to ensure the language server finds it in the project root.