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[stable] Further revert Deref for Cow to its 1.90.0 state #148216

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Merged
merged 1 commit into from
Oct 28, 2025
+8 −4
Merged

[stable] Further revert Deref for Cow to its 1.90.0 state #148216

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3 changes: 2 additions & 1 deletion library/alloc/src/borrow.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -333,7 +333,8 @@ impl<B: ?Sized + ToOwned> Cow<'_, B> {
// #[rustc_const_unstable(feature = "const_convert", issue = "143773")]
#[stable(feature = "rust1", since = "1.0.0")]
impl<B: ?Sized + ToOwned> Deref for Cow<'_, B>
// where
where
B::Owned: Borrow<B>,
// B::Owned: [const] Borrow<B>,
{
type Target = B;
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9 changes: 6 additions & 3 deletions tests/ui/traits/generic-cow-inference-regression.rs
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Expand Up @@ -5,9 +5,12 @@

use std::borrow::{Cow, Borrow};

pub fn generic_deref<'a, T: ToOwned<Owned = U>, U>(cow: Cow<'a, T>) {
let _: &T = &cow;
}
// This won't work even with the non-const bound on `Deref` like 1.90.0, although note
// as well that no such bound existed until 1.57 started `~const` experiments.
//
// pub fn generic_deref<'a, T: ToOwned<Owned = U>, U>(cow: Cow<'a, T>) {
// let _: &T = &cow;
// }

pub fn generic_borrow<'a, T: ToOwned<Owned = U>, U>(cow: Cow<'a, T>) {
let _: &T = cow.borrow();
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