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Don't derive `PartialEq::ne`. Currently we skip deriving `PartialEq::ne` for C-like (fieldless) enums and empty structs, thus reyling on the default `ne`. This behaviour is unnecessarily conservative, because the `PartialEq` docs say this: > Implementations must ensure that eq and ne are consistent with each other: > > `a != b` if and only if `!(a == b)` (ensured by the default > implementation). This means that the default implementation (`!(a == b)`) is always good enough. So this commit changes things such that `ne` is never derived. The motivation for this change is that not deriving `ne` reduces compile times and binary sizes. Observable behaviour may change if a user has defined a type `A` with an inconsistent `PartialEq` and then defines a type `B` that contains an `A` and also derives `PartialEq`. Such code is already buggy and preserving bug-for-bug compatibility isn't necessary. Two side-effects of the change: - There is only one error message produced for types where `PartialEq` cannot be derived, instead of two. - For coverage reports, some warnings about generated `ne` methods not being executed have disappeared. Both side-effects seem fine, and possibly preferable. |
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