Code

#[repr(C)] // <--
pub struct Foo {
    pub i: i16,
    align: i16
}

Current output

warning: field `align` is never read
 --> src/lib.rs:3:5
  |
1 | pub struct Foo {
  |            --- field in this struct
2 |     pub i: i16,
3 |     align: i16
  |     ^^^^^
  |
  = note: `#[warn(dead_code)]` on by default

Desired output

No warnings, or perhaps a different warning.

Rationale and extra context

This warning is probably triggering because there's no constructor that allows a user to set the align field on struct Foo. However, there is still a valid way for a user to construct it: std::mem::zeroed(). The libc crate contains many structs that must be initialized that way. libc could silence these warnings by #[allow(dead_code)], but that's too broad a brush. It would silence many much more serious warnings. Could we please either revert to the previous behavior, or else create a new lint for this that can be separately silenced?

Other cases

No response

Rust Version

rustc 1.80.0-nightly (804421dff 2024-06-07)
binary: rustc
commit-hash: 804421dff5542c9c7da5c60257b5dbc849719505
commit-date: 2024-06-07
host: x86_64-unknown-freebsd
release: 1.80.0-nightly
LLVM version: 18.1.7

Anything else?

This is a regression since rustc 1.80.0-nightly (f67a1acc0 2024-06-01). That version did not warn in such cases.

Downstream issue: rust-lang/libc#3740