Tracking Issue for `BYTE_SLICE_IN_PACKED_STRUCT_WITH_DERIVE` lint

[nnethercote]

This is a tracking issue for the BYTE_SLICE_IN_PACKED_STRUCT_WITH_DERIVE lint, which is being added in #104429. The lint detects cases where derive is used with a packed struct that contains a [u8] field.

Example

This lint will trigger for code like this:

#[repr(packed)]
#[derive(Eq, PartialEq)]
pub struct FlexZeroSlice {
    width: u8,
    data: [u8], // triggered
}

At some point in the future this case will be disallowed.

See #104429 for more details, especially the t-lang nomination.

[est31]

@rustbot label C-future-compatibility

[traviscross]

@rustbot labels +I-lang-nominated

Let's discuss whether we want to disallow this in Rust 2024.