## REPR_TRANSPARENT_EXTERNAL_PRIVATE_FIELDS

# Static REPR_TRANSPARENT_EXTERNAL_PRIVATE_FIELDS

Source

    pub static REPR_TRANSPARENT_EXTERNAL_PRIVATE_FIELDS: &'static Lint

Expand description

The `repr_transparent_external_private_fields` lint detects types marked `#[repr(transparent)]` that (transitively) contain an external ZST type marked `#[non_exhaustive]` or containing private fields

#### §Example

ⓘ

    #![deny(repr_transparent_external_private_fields)]
    use foo::NonExhaustiveZst;

    #[repr(transparent)]
    struct Bar(u32, ([u32; 0], NonExhaustiveZst));

This will produce:

    error: zero-sized fields in repr(transparent) cannot contain external non-exhaustive types
     --> src/main.rs:5:28
      |
    5 | struct Bar(u32, ([u32; 0], NonExhaustiveZst));
      |                            ^^^^^^^^^^^^^^^^
      |
    note: the lint level is defined here
     --> src/main.rs:1:9
      |
    1 | #![deny(repr_transparent_external_private_fields)]
      |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
      = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
      = note: for more information, see issue #78586 <https://github.com/rust-lang/rust/issues/78586>
      = note: this struct contains `NonExhaustiveZst`, which is marked with `#[non_exhaustive]`, and makes it not a breaking change to become non-zero-sized in the future.

#### §Explanation

Previous, Rust accepted fields that contain external private zero-sized types, even though it should not be a breaking change to add a non-zero-sized field to that private type.

This is a future-incompatible lint to transition this to a hard error in the future. See issue #78586 for more details.