Error in derived PartialOrd impl on structs with mut reference fields

[arkeet]

This fails to compile, with a rather cryptic error message: [playground]

#[derive(PartialEq, PartialOrd)]
struct Bad<'a>(&'a mut u8);

This is one of the errors in the expanded code (the rest are similar):

// error[E0389]: cannot borrow data mutably in a `&` reference
fn lt(&self, __arg_0: &Bad<'a>) -> bool {
    match *__arg_0 {
        Bad(ref __self_1_0) =>
//          -------------- consider changing this to `ref mut __self_1_0`
        match *self {
            Bad(ref __self_0_0) =>
            (*__self_0_0) < (*__self_1_0) ||
//                          ^^^^^^^^^^^^^ assignment into an immutable reference
                !((*__self_1_0) < (*__self_0_0)) && false,
        },
    }
}

Seems quite similar to #15689.

[durka]

Why is the derive code dereferencing the captures‽ There's a forwarding impl!

rust/src/libcore/cmp.rs

Lines 943 to 951 in 1e60a47

	// &mut pointers
	#[stable(feature = "rust1", since = "1.0.0")]
	impl<'a, 'b, A: ?Sized, B: ?Sized> PartialEq<&'b mut B> for &'a mut A where A: PartialEq<B> {
	#[inline]
	fn eq(&self, other: &&'b mut B) -> bool { PartialEq::eq(*self, *other) }
	#[inline]
	fn ne(&self, other: &&'b mut B) -> bool { PartialEq::ne(*self, *other) }
	}

[Mark-Simulacrum]

Appears to work today. Closing.