rust/library/core
bors 361c599fee Auto merge of #98655 - nnethercote:dont-derive-PartialEq-ne, r=dtolnay
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.
2022-08-18 10:11:11 +00:00
..
benches Rename integer log* methods to ilog* 2022-08-09 10:20:49 -07:00
primitive_docs
src Auto merge of #98655 - nnethercote:dont-derive-PartialEq-ne, r=dtolnay 2022-08-18 10:11:11 +00:00
tests fix(iter::skip): Optimize next and nth implementations of Skip 2022-08-14 13:25:13 -04:00
Cargo.toml Avoid use of rand::thread_rng in stdlib benchmarks 2022-05-02 00:08:21 -07:00