clangd

What is clangd?

clangd understands your C++ code and adds smart features to your editor: code completion, compile errors, go-to-definition and more.

clangd is a language server that implements the Language Server Protocol; it can work with many editors through a plugin. Here's Visual Studio Code with the clangd plugin, demonstrating code completion:

clangd is based on the Clang C++ compiler, and is part of the LLVM project.