`unused_parens` should lint superfluous parentheses on the LHS of an assignment

[fanzier]

I tried this code:

#[deny(unused_parens)]

fn main() {
    let mut a = 5;
    (((((a))))) = 6;
}

I expected to see this happen: the compiler should reject this because there are unused parentheses on the left-hand side of the assignment.

Instead, this happened: the code compiled without errors.

Meta

This bug exists on current stable, beta and nightly.