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Bootstrap derive(PartialEq) (#163)#473

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163-eq-derive
May 29, 2025
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Bootstrap derive(PartialEq) (#163)#473
tyranron merged 23 commits into
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163-eq-derive

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@tyranron tyranron commented May 26, 2025 •
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Part of #163

Synopsis

This PR is the initial part of #163 and adds only structural expansion of derive(PartialEq).

Solution

Mirrors the PartialEq expansion of std, but applies trait bounds for generics correctly.

Checklist

  • Documentation is updated
  • Tests are added/updated
  • CHANGELOG entry is added

@tyranron tyranron added this to the 2.1.0 milestone May 26, 2025
@tyranron tyranron self-assigned this May 26, 2025
@tyranron tyranron added enhancement feature New derive or feature labels May 26, 2025
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tyranron commented May 26, 2025 •
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I plan to add more features in the follow-up PRs:

  • Implement PartialEq::ne() method (std omits it) to allow better performance for cases when it's optimized.
  • Support #[partial_eq(skip)] attribute.
  • Support #[partial_eq(where(<bounds>))] attribute (required when fields may contain private types).
  • Implement forwarding expansion for newtypes (single-field structs) with #[partial_eq(forward)] support.
  • Finally, support #[partial_eq(<types>)] to allow the case requested in Feature idea: PartialEq and PartialOrd for the wrapped type #163.
  • Implement derive(Eq) expanding as impl <T> Eq for Type<T> where Self: PartialEq {}.

@tyranron tyranron linked an issue May 26, 2025 that may be closed by this pull request
Feature idea: PartialEq and PartialOrd for the wrapped type #163
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@tyranron tyranron mentioned this pull request May 26, 2025
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@tyranron tyranron mentioned this pull request May 27, 2025
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tyranron added a commit that referenced this pull request May 27, 2025
@tyranron
Consider associative types in utils::GenericsSearch (#474)
07dc39d 
Revealed from #473

## Synopsis

`utils::GenericsSearch` doesn't consider associative type, leading to
missing trait bounds in `AsRef`/`AsMut` expansions.

```rust
#[derive(AsRef)]
#[as_ref(forward)]
struct Forward<T: Some> {
    first: T::Assoc,
}
```
expands as:
```rust
#[allow(deprecated)]
#[allow(unreachable_code)]
#[automatically_derived]
impl<T: Some, __AsT: ?derive_more::core::marker::Sized> derive_more::core::convert::AsRef<__AsT> for Forward<T>
{
    #[inline]
    fn as_ref(&self) -> &__AsT { <T::Assoc as derive_more::core::convert::AsRef<__AsT>>::as_ref(&self.first) }
}
```
but should expand as:
```rust
#[allow(deprecated)]
#[allow(unreachable_code)]
#[automatically_derived]
impl<T: Some, __AsT: ?derive_more::core::marker::Sized> derive_more::core::convert::AsRef<__AsT> for Forward<T>
where
    T::Assoc: derive_more::core::convert::AsRef<__AsT>,
{
    #[inline]
    fn as_ref(&self) -> &__AsT { <T::Assoc as derive_more::core::convert::AsRef<__AsT>>::as_ref(&self.first) }
}
```

## Solution

This PR fixes this situation and covers associative types usage in
`AsRef`/`AsMut` tests.

## Additionally

Improves `utils::GenericsSearch` performance by early returns (stop
`Visit`ing whenever something is found).

Also, unit tests for `utils::GenericsSearch` are added.
@tyranron tyranron marked this pull request as ready for review May 27, 2025 21:24
@tyranron tyranron enabled auto-merge (squash) May 27, 2025 21:25
@tyranron tyranron requested a review from JelteF May 27, 2025 21:30
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tyranron commented May 27, 2025

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@JelteF note: I named Cargo feature eq, because:

  1. I think it makes sense to keep both Eq and PartialEq derives under the same feature, as we do for AsRef/AsMut, and so, keep even the same documentation page for both of them.
  2. I think that using #[eq] helper attribute for derive(PartialEq) (like #[eq(skip)]) is more ergonomic, since derive(Eq) won't need any helper attributes at all.

@tyranron tyranron mentioned this pull request May 28, 2025
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tyranron commented May 29, 2025

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ping @JelteF

@tyranron tyranron merged commit 47d8c10 into master May 29, 2025
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@tyranron tyranron deleted the 163-eq-derive branch May 29, 2025 14:11
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Feature idea: PartialEq and PartialOrd for the wrapped type

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