E0554 error when installing Racer: #![feature] cannot be used in stable Rust version

Hello everyone! I'm new to Rust and trying to set up a development environment. I decided to install Racer (code autocompletion) via Cargo. I ran the command: ```bash cargo install racer ``` But got the error: ``` error[E0554]: #![feature] may not be used on the stable release channel ``` I'm using Windows 10, Rust installed via rustup. I checked the version: ``` rustc --version rustc 1.70.0 (stable) ``` Here's the full error log (abbreviated): ``` error[E0554]: #![feature] may not be used on the stable release channel --> C:\Users\me\.cargo\registry\src\...\racer-2.1.51\src\lib.rs:1:1 | 1 | #![feature(plugin)] | ^^^^^^^^^^^^^^^^^^^^ ``` I don't understand what `#![feature]` is and why it doesn't work on the stable channel. I tried updating Rust (`rustup upd