Error which must not be

For programming on rust I use vs code and the rust-analyzer plugin. When I want to import some module,which I has already installed, this plugin marks this line of code as error. How I can fix it, rust-analyser's developers?

The extern crate declaration is no longer necessary since the 2018 edition of Rust. You should simply add regex to your Cargo.toml, and then you will be able to use it.

If you need further help, then you have to give us an actual error message.