I can recommend https://tabnine.com/ with https://github.com/rust-analyzer/rust-analyzer .

While rust-analyzer doesn't always resolve type (unlike Jetbrains Rust plugin, which always does but sometimes incorrectly), it still makes writing code faster and doesn't have RLS quirks (which come from the fact that RLS has to compile the code before offering suggestions, so code has to be correct at some point, which is not good if you are prototyping)