Rust error E0002: #### Note: this error code is no longer emitted by the compiler

The compiler team's explanation

Note: this error code is no longer emitted by the compiler.

This error indicates that an empty match expression is invalid because the type it is matching on is non-empty (there exist values of this type). In safe code it is impossible to create an instance of an empty type, so empty match expressions are almost never desired. This error is typically fixed by adding one or more cases to the match expression.

An example of an empty type is enum Empty { }. So, the following will work:

enum Empty {}

fn foo(x: Empty) {
    match x {
        // empty
    }
}

However, this won't:

fn foo(x: Option<String>) {
    match x {
        // empty
    }
}

From rustc --explain E0002 (1.99.0), part of the Rust project, MIT or Apache-2.0. Official page.