Impls and impl items inherit lint levels of the corresponding traits and trait items

[mu001999]

https://github.com/rust-lang/rust/blob/master/compiler/rustc_passes/src/dead.rs#L360-L361 won't insert assoc items into the live set, so that impl items cannot be marked live.

This PR lets impls and impl items can inherit lint levels of the corresponding traits and trait items.

Fixes #144060

r? @petrochenkov

[compiler-errors]

This behavior seems really non-local and pretty broad. #[allow(dead_code)] on a trait definition suppresses all dead code warnings in all impls with this change?

[mu001999]

#[allow(dead_code)] on a trait definition suppresses all dead code warnings in all impls with this change?

@compiler-errors yes, and I think this makes sense. We would have only one trait definition but many impls, letting #[allow(dead_code)] on traits propagate to impls is convenient. Otherwise we need to add #[allow(dead_code)] also on each impls which use unused items.

[petrochenkov]

r? @compiler-errors

[petrochenkov]

Hmm, why did rustbot assign it to me again?
I'll just block this on #144863 now.
@rustbot blocked

[mu001999]

Hmm, why did rustbot assign it to me again?

I tried reassigning, but rustbot didn’t respond after waiting a while, so I deleted the comment. 😂

[bors]

☔ The latest upstream changes (presumably #144863) made this pull request unmergeable. Please resolve the merge conflicts.