How to get real time cargo check editing experience without "manually check on save"?

[Wyvern]

Hi, I previously used rust official extension, it could always check / watch my editing .rs files and give results immediately.

After switch to rust-analyzer I lost this capability, always need "check on save"; it's not good for general users.

Is there a way to get always check function, or how to config/set to activate it?

[bjorn3]

Duplicate of #3107

tl;dr: rls used an unstable compiler api to provide rustc with the contents of the files as provided by the editor. Rust-analyzer doesn't use unstable api's, so it has to use cargo check, which requires the files to be saved on the disk.

[lnicola]

Syntax errors and other diagnostics are already refreshed during editing. If you want the full rustc diagnostics set, you can save periodically, or you can configure your editor to save the files automatically (at the cost of some CPU usage).

Full on-the-fly diagnostics are tracked in #3107.