dead_code lint does not trigger for tuple structs with unread fields

@FabianWolff

This code:

fn main() { let _ = Example { u: 0 }; } struct Example { u: u8, }

Produces this warning:

warning: field is never read: `u` --> src/main.rs:6:5 | 6 | u: u8, | ^^^^^ |

However, switching to a tuple struct:

fn main() { let _ = Example(0); } struct Example(u8);

Does not report a warning.

Original report misleadingly focusing on Debug

fn main() { dbg!(Example { a: 0 }); } #[derive(Debug)] struct Example { a: u8, }

produces

warning: field is never read: `a` --> src/main.rs:7:5 | 7 | a: u8, | ^^^^^ | = note: `#[warn(dead_code)]` on by default

However, switching to a tuple struct:

fn main() { dbg!(Example(0)); } #[derive(Debug)] struct Example(u8);

does not produce the warning.

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