Autocomplete (in fact multiple competing implementations) has been available for more than a decade. There are dozens of sources of autocomplete data depending on your language of choice.

The best one I have found for C++ is rtags which uses clang as backend and it is magical when it works. Unfortunately the latency was just high enough to get in the way of my work especially after switching branches and the server being busy reindexing the codebase.

It was more than 3 years ago though, it is probably time to give it another try.

I must've named the wrong feature, but I mean VSC's language inference abilities and API. I've been waiting for years for other editors to get something like that. All other editors have something like snippets or autocomplete matching for keywords.

You can get intellisense in neovim with coc.nvim[0], which supports the full language server protocol. I've got it running with several VSCode extensions ported over to coc extensions, as well as the Microsoft Python Language Server.

[0]: https://github.com/neoclide/coc.nvim

Emacs supports LSP and many many other autocomplete sources.