Most features can be covered by a few VSCode extensions like these:
https://marketplace.visualstudio.com/items?itemName=yzhang.m...
https://marketplace.visualstudio.com/items?itemName=mushan.v...
Other code editors probably have similar extensions and syncing the notes could be done with Dropbox/git/whatever...
I am also surprised how well https://tabnine.com/ works with auto-completion for arbitrary notes.