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

[cuviper]

It's not clear whether it breaks anything to not have this bound,
but the conservative choice is to match the state as of 1.90.0.

See also:
#147964 (comment)
https://rust-lang.zulipchat.com/#narrow/channel/144729-t-types/topic/Can.20this.20change.20break.20code.20in.201.2E91.3F/with/547528362

[rustbot]

r? @BoxyUwU

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[BoxyUwU]

lgtm assuming this is the only difference from a proper revert 👍 libs signed off on wanting the revert to be to 1.90 instead of the really old version. don't know if you also want them to actually review the diff itself or you're fine with my approval. up to you

View changes since this review

[cuviper]

For reference:

$ git diff 1.90.0 library/alloc/src/borrow.rs
diff --git a/library/alloc/src/borrow.rs b/library/alloc/src/borrow.rs
index 07f51b7614ff..d982e46e08af 100644
--- a/library/alloc/src/borrow.rs
+++ b/library/alloc/src/borrow.rs
@@ -16,10 +16,13 @@
 #[cfg(not(no_global_oom_handling))]
 use crate::string::String;

+// FIXME(inference): const bounds removed due to inference regressions found by crater;
+//   see https://github.com/rust-lang/rust/issues/147964
+// #[rustc_const_unstable(feature = "const_convert", issue = "143773")]
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<'a, B: ?Sized> Borrow<B> for Cow<'a, B>
-where
-    B: ToOwned,
+impl<'a, B: ?Sized + ToOwned> Borrow<B> for Cow<'a, B>
+// where
+//     B::Owned: [const] Borrow<B>,
 {
     fn borrow(&self) -> &B {
         &**self
@@ -325,10 +328,14 @@ pub fn into_owned(self) -> <B as ToOwned>::Owned {
     }
 }

+// FIXME(inference): const bounds removed due to inference regressions found by crater;
+//   see https://github.com/rust-lang/rust/issues/147964
+// #[rustc_const_unstable(feature = "const_convert", issue = "143773")]
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<B: ?Sized + ToOwned> Deref for Cow<'_, B>
 where
     B::Owned: Borrow<B>,
+//     B::Owned: [const] Borrow<B>,
 {
     type Target = B;

@@ -438,8 +445,14 @@ fn hash<H: Hasher>(&self, state: &mut H) {
     }
 }

+// FIXME(inference): const bounds removed due to inference regressions found by crater;
+//   see https://github.com/rust-lang/rust/issues/147964
+// #[rustc_const_unstable(feature = "const_convert", issue = "143773")]
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<T: ?Sized + ToOwned> AsRef<T> for Cow<'_, T> {
+impl<T: ?Sized + ToOwned> AsRef<T> for Cow<'_, T>
+// where
+//     T::Owned: [const] Borrow<T>,
+{
     fn as_ref(&self) -> &T {
         self
     }

[jackh726]

r=me

View changes since this review

[cuviper]

@bors r=BoxyUwU,jackh726 rollup=never p=1000

[bors]

📌 Commit faf3e0b has been approved by BoxyUwU,jackh726

It is now in the queue for this repository.

[bors]

⌛ Testing commit faf3e0b with merge f8297e3...

[bors]

☀️ Test successful - checks-actions
Approved by: BoxyUwU,jackh726
Pushing f8297e3 to stable...