Pattern matching reborrowing

Hello, sometimes you want to work with intermediate variables with pattern matching, but when introducing @ bindings rust gives an error cannot borrow value as mutable more than once at a time value is mutably borrowed by 'a' here. But the same code can be made working if just split it into 2 pattern matches.

struct A(B);
struct B(i32);

fn main() {
    works(A(B(1)));
    not_works(A(B(1)));
}

fn not_works(mut foo: A) {
    if let A(a @ B(b)) = &mut foo {
        *b += 1;
        *a = B(8);
    }
}

fn works(mut foo: A) {
    if let A(a) = &mut foo {
        if let B(b) = a {
            *b += 1;
            *a = B(8);
        }
    }
}

Start by compiling the not_works and works functions in the reproducer and compare their pattern-matching behavior. Investigate why the @ binding causes the mutable-borrow error while the nested match succeeds; done means establishing consistent, accepted behavior for the equivalent patterns and covering the case with a regression test.