rust/src/librustc_error_codes/error_codes/E0162.md

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

An if-let pattern attempts to match the pattern, and enters the body if the match was successful. If the match is irrefutable (when it cannot fail to match), use a regular let-binding instead. For instance:

struct Irrefutable(i32);
let irr = Irrefutable(0);

// This fails to compile because the match is irrefutable.
if let Irrefutable(x) = irr {
    // This body will always be executed.
    // ...
}

Try this instead:

struct Irrefutable(i32);
let irr = Irrefutable(0);

let Irrefutable(x) = irr;
println!("{}", x);