[0.2] Backport "cleanup: Use derived traits as much as possible"#4814
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tgross35 merged 1 commit intorust-lang:libc-0.2from Nov 4, 2025
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Historically Rust hasn't supported derives on packed structs well, and until recently our automatic derives via `s!` still did not support these (fixed by 79d1bdb ("Flip `Copy` and `PartialEq, Hash` derives")). This meant that any packed struct implementing `extra_traits` had handwritten implementations that are no longer needed. There are also a handful of cases that use a handwritten implementation in order to selectively exclude padding fields. Others don't seem to be handwritten for any specific reason. Clean up all of the above by switching from `s_no_extra_traits!` to `s!` and deleting the handwritten implementations wherever possible. The only remaining handwritten implementations are those that compare unions with `unsafe` (which will have to be addressed) or floats. Note that in some cases, this means we are no longer excluding padding fields from comparisons. These traits are only usable via references, not raw pointers; thus, the user has asserted that they are initialized, and there is no UB in `libc` by reading them. Practically the only way to know they are initialized is by starting with a zeroed struct, so in most cases they will have no effect on the results. Whether or not padding fields are included in handwritten traits is also completely inconsistent (most include them), so there isn't much predictability lost here. The new `Padding` type will also improve the situation here in the future. (backport <rust-lang#4806>) (cherry picked from commit 141aea1) [ note that this was very conflict-heavy so the cherry pick differs quite a bit from the original commit - Trevor ]
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Backport for #4806