fix #[derive] implementation for repr(packed) structs

Fix the derive implementation for repr(packed) structs to move the
fields out instead of calling functions on references to each subfield.

That's it, `#[derive(PartialEq)]` on a packed struct now does:
```Rust
fn eq(&self, other: &Self) {
    let field_0 = self.0;
    let other_field_0 = other.0;
    &field_0 == &other_field_0
}
```

Instead of
```Rust
fn eq(&self, other: &Self) {
    let ref field_0 = self.0;
    let ref other_field_0 = other.0;
    &*field_0 == &*other_field_0
}
```

Taking (unaligned) references to each subfield is undefined, unsound and
is an error with MIR effectck, so it had to be prevented. This causes
a borrowck error when a `repr(packed)` struct has a non-Copy field (and
therefore is a [breaking-change]), but I don't see a sound way to avoid
that error.

0 files changed, 0 insertions, 0 deletions