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feat: add symmetric PartialEq impls for Vec, &[T], &mut [T] versus Cow<'_, [T]> #156160

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feat: add symmetric PartialEq impls for Vec, &[T], &mut [T] versus Cow<'_, [T]> #156160

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33c76f3
feat: add symmetric PartialEq impls for Vec/slices vs Cow<[T]>
kx0101 May 4, 2026
3451d8a
Bless UI tests for new PartialEq<Cow<[U]>> impls
kx0101 May 5, 2026
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6 changes: 6 additions & 0 deletions library/alloc/src/vec/partial_eq.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -32,6 +32,12 @@ __impl_slice_eq1! { [A: Allocator] Cow<'_, [T]>, Vec<U, A> where T: Clone, #[sta
__impl_slice_eq1! { [] Cow<'_, [T]>, &[U] where T: Clone, #[stable(feature = "rust1", since = "1.0.0")] }
#[cfg(not(no_global_oom_handling))]
__impl_slice_eq1! { [] Cow<'_, [T]>, &mut [U] where T: Clone, #[stable(feature = "rust1", since = "1.0.0")] }
#[cfg(not(no_global_oom_handling))]
__impl_slice_eq1! { [A: Allocator] Vec<T, A>, Cow<'_, [U]> where U: Clone, #[stable(feature = "partialeq_cow_for_vec_and_slice", since = "CURRENT_RUSTC_VERSION")] }
#[cfg(not(no_global_oom_handling))]
__impl_slice_eq1! { [] &[T], Cow<'_, [U]> where U: Clone, #[stable(feature = "partialeq_cow_for_vec_and_slice", since = "CURRENT_RUSTC_VERSION")] }
#[cfg(not(no_global_oom_handling))]
__impl_slice_eq1! { [] &mut [T], Cow<'_, [U]> where U: Clone, #[stable(feature = "partialeq_cow_for_vec_and_slice", since = "CURRENT_RUSTC_VERSION")] }
__impl_slice_eq1! { const, [A: Allocator, const N: usize] Vec<T, A>, [U; N], #[rustc_const_unstable(feature = "const_cmp", issue = "143800")] #[stable(feature = "rust1", since = "1.0.0")] }
__impl_slice_eq1! { const, [A: Allocator, const N: usize] Vec<T, A>, &[U; N], #[rustc_const_unstable(feature = "const_cmp", issue = "143800")] #[stable(feature = "rust1", since = "1.0.0")] }

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19 changes: 19 additions & 0 deletions library/alloctests/tests/vec.rs
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Expand Up @@ -1322,6 +1322,25 @@ fn test_from_cow() {
assert_eq!(Vec::from(Cow::Owned(owned)), vec!["owned", "(vec)"]);
}

#[test]
fn test_partial_eq_cow_symmetric() {
let v: Vec<i32> = vec![1, 2, 3];
let c: Cow<'_, [i32]> = Cow::Borrowed(&[1, 2, 3]);

assert_eq!(c, v);
assert_eq!(v, c);

let s: &[i32] = &[1, 2, 3];
assert_eq!(s, c);

let mut arr = [1, 2, 3];
let ms: &mut [i32] = &mut arr;
assert_eq!(ms, c);

let v2: Vec<i32> = vec![1, 2, 4];
assert!(v2 != c);
}

#[allow(dead_code)]
fn assert_covariance() {
fn drain<'new>(d: Drain<'static, &'static str>) -> Drain<'new, &'new str> {
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6 changes: 3 additions & 3 deletions tests/ui/consts/too_generic_eval_ice.current.stderr
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Expand Up @@ -30,15 +30,15 @@ LL | [5; Self::HOST_SIZE] == [6; 0]
|
= help: the trait `PartialEq<[{integer}; 0]>` is not implemented for `[{integer}; Self::HOST_SIZE]`
= help: the following other types implement trait `PartialEq<Rhs>`:
`&[T]` implements `PartialEq<Cow<'_, [U]>>`
`&[T]` implements `PartialEq<Vec<U, A>>`
`&[T]` implements `PartialEq<[U; N]>`
`&[u8; N]` implements `PartialEq<ByteStr>`
`&[u8; N]` implements `PartialEq<ByteString>`
`&[u8]` implements `PartialEq<ByteStr>`
`&[u8]` implements `PartialEq<ByteString>`
`&mut [T]` implements `PartialEq<Vec<U, A>>`
`&mut [T]` implements `PartialEq<[U; N]>`
and 11 others
`&mut [T]` implements `PartialEq<Cow<'_, [U]>>`
and 13 others

error: aborting due to 4 previous errors

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12 changes: 6 additions & 6 deletions tests/ui/macros/assert-ne-no-invalid-help-issue-146204.stderr
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Expand Up @@ -6,15 +6,15 @@ LL | assert_ne!(buf, b"----");
|
= help: the trait `PartialEq<&[u8; 4]>` is not implemented for `[u8; 4]`
= help: the following other types implement trait `PartialEq<Rhs>`:
`&[T]` implements `PartialEq<Cow<'_, [U]>>`
`&[T]` implements `PartialEq<Vec<U, A>>`
`&[T]` implements `PartialEq<[U; N]>`
`&[u8; N]` implements `PartialEq<ByteStr>`
`&[u8; N]` implements `PartialEq<ByteString>`
`&[u8]` implements `PartialEq<ByteStr>`
`&[u8]` implements `PartialEq<ByteString>`
`&mut [T]` implements `PartialEq<Vec<U, A>>`
`&mut [T]` implements `PartialEq<[U; N]>`
and 11 others
`&mut [T]` implements `PartialEq<Cow<'_, [U]>>`
and 13 others

error[E0277]: can't compare `[u8; 4]` with `&[u8; 4]`
--> $DIR/assert-ne-no-invalid-help-issue-146204.rs:19:5
Expand All @@ -24,15 +24,15 @@ LL | assert_eq!(buf, b"----");
|
= help: the trait `PartialEq<&[u8; 4]>` is not implemented for `[u8; 4]`
= help: the following other types implement trait `PartialEq<Rhs>`:
`&[T]` implements `PartialEq<Cow<'_, [U]>>`
`&[T]` implements `PartialEq<Vec<U, A>>`
`&[T]` implements `PartialEq<[U; N]>`
`&[u8; N]` implements `PartialEq<ByteStr>`
`&[u8; N]` implements `PartialEq<ByteString>`
`&[u8]` implements `PartialEq<ByteStr>`
`&[u8]` implements `PartialEq<ByteString>`
`&mut [T]` implements `PartialEq<Vec<U, A>>`
`&mut [T]` implements `PartialEq<[U; N]>`
and 11 others
`&mut [T]` implements `PartialEq<Cow<'_, [U]>>`
and 13 others

error[E0277]: can't compare `[u8; 4]` with `&[u8; 4]`
--> $DIR/assert-ne-no-invalid-help-issue-146204.rs:5:30
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