For all the C/C++ developers who use #Emacs: The wonderful RTags system is still the best tool for autocompletion and codenavigation, I think: https://github.com/Andersbakken/rtags/

Current linux brew installs crash however, as llvm 13.x and higher have some regression. Workaround:

brew edit rtags
# edit dependency "llvm" to say "llvm@9"
brew reinstall -s rtags

And voila! It works again! rtags is super fast on large projects. Needs compile_commands.json, e.g. from CMake!