Document (internally) that Range*<&T> as RangeBounds<T> impls are intentionally not T: ?Sized, and document (publically) an alternative.

Author: zachs18

core/src/ops/range.rs

@@ -1141,6 +1141,12 @@ impl<'a, T: ?Sized + 'a> RangeBounds<T> for (Bound<&'a T>, Bound<&'a T>) {
     }
 }
 
+// This impl intentionally does not have `T: ?Sized`;
+// see https://github.com/rust-lang/rust/pull/61584 for discussion of why.
+//
+/// If you need to use this implementation where `T` is unsized,
+/// consider using the `RangeBounds` impl for a 2-tuple of [`Bound<&T>`][Bound],
+/// i.e. replace `start..` with `(Bound::Included(start), Bound::Unbounded)`.
 #[stable(feature = "collections_range", since = "1.28.0")]
 impl<T> RangeBounds<T> for RangeFrom<&T> {
     fn start_bound(&self) -> Bound<&T> {
@@ -1151,6 +1157,12 @@ impl<T> RangeBounds<T> for RangeFrom<&T> {
     }
 }
 
+// This impl intentionally does not have `T: ?Sized`;
+// see https://github.com/rust-lang/rust/pull/61584 for discussion of why.
+//
+/// If you need to use this implementation where `T` is unsized,
+/// consider using the `RangeBounds` impl for a 2-tuple of [`Bound<&T>`][Bound],
+/// i.e. replace `..end` with `(Bound::Unbounded, Bound::Excluded(end))`.
 #[stable(feature = "collections_range", since = "1.28.0")]
 impl<T> RangeBounds<T> for RangeTo<&T> {
     fn start_bound(&self) -> Bound<&T> {
@@ -1161,6 +1173,12 @@ impl<T> RangeBounds<T> for RangeTo<&T> {
     }
 }
 
+// This impl intentionally does not have `T: ?Sized`;
+// see https://github.com/rust-lang/rust/pull/61584 for discussion of why.
+//
+/// If you need to use this implementation where `T` is unsized,
+/// consider using the `RangeBounds` impl for a 2-tuple of [`Bound<&T>`][Bound],
+/// i.e. replace `start..end` with `(Bound::Included(start), Bound::Excluded(end))`.
 #[stable(feature = "collections_range", since = "1.28.0")]
 impl<T> RangeBounds<T> for Range<&T> {
     fn start_bound(&self) -> Bound<&T> {
@@ -1171,6 +1189,12 @@ impl<T> RangeBounds<T> for Range<&T> {
     }
 }
 
+// This impl intentionally does not have `T: ?Sized`;
+// see https://github.com/rust-lang/rust/pull/61584 for discussion of why.
+//
+/// If you need to use this implementation where `T` is unsized,
+/// consider using the `RangeBounds` impl for a 2-tuple of [`Bound<&T>`][Bound],
+/// i.e. replace `start..=end` with `(Bound::Included(start), Bound::Included(end))`.
 #[stable(feature = "collections_range", since = "1.28.0")]
 impl<T> RangeBounds<T> for RangeInclusive<&T> {
     fn start_bound(&self) -> Bound<&T> {
@@ -1181,6 +1205,12 @@ impl<T> RangeBounds<T> for RangeInclusive<&T> {
     }
 }
 
+// This impl intentionally does not have `T: ?Sized`;
+// see https://github.com/rust-lang/rust/pull/61584 for discussion of why.
+//
+/// If you need to use this implementation where `T` is unsized,
+/// consider using the `RangeBounds` impl for a 2-tuple of [`Bound<&T>`][Bound],
+/// i.e. replace `..=end` with `(Bound::Unbounded, Bound::Included(end))`.
 #[stable(feature = "collections_range", since = "1.28.0")]
 impl<T> RangeBounds<T> for RangeToInclusive<&T> {
     fn start_bound(&self) -> Bound<&T> {

core/src/range.rs

@@ -167,6 +167,12 @@ impl<T> RangeBounds<T> for Range<T> {
     }
 }
 
+// This impl intentionally does not have `T: ?Sized`;
+// see https://github.com/rust-lang/rust/pull/61584 for discussion of why.
+//
+/// If you need to use this implementation where `T` is unsized,
+/// consider using the `RangeBounds` impl for a 2-tuple of [`Bound<&T>`][Bound],
+/// i.e. replace `start..end` with `(Bound::Included(start), Bound::Excluded(end))`.
 #[unstable(feature = "new_range_api", issue = "125687")]
 impl<T> RangeBounds<T> for Range<&T> {
     fn start_bound(&self) -> Bound<&T> {
@@ -346,6 +352,12 @@ impl<T> RangeBounds<T> for RangeInclusive<T> {
     }
 }
 
+// This impl intentionally does not have `T: ?Sized`;
+// see https://github.com/rust-lang/rust/pull/61584 for discussion of why.
+//
+/// If you need to use this implementation where `T` is unsized,
+/// consider using the `RangeBounds` impl for a 2-tuple of [`Bound<&T>`][Bound],
+/// i.e. replace `start..=end` with `(Bound::Included(start), Bound::Included(end))`.
 #[unstable(feature = "new_range_api", issue = "125687")]
 impl<T> RangeBounds<T> for RangeInclusive<&T> {
     fn start_bound(&self) -> Bound<&T> {
@@ -491,6 +503,12 @@ impl<T> RangeBounds<T> for RangeFrom<T> {
     }
 }
 
+// This impl intentionally does not have `T: ?Sized`;
+// see https://github.com/rust-lang/rust/pull/61584 for discussion of why.
+//
+/// If you need to use this implementation where `T` is unsized,
+/// consider using the `RangeBounds` impl for a 2-tuple of [`Bound<&T>`][Bound],
+/// i.e. replace `start..` with `(Bound::Included(start), Bound::Unbounded)`.
 #[unstable(feature = "new_range_api", issue = "125687")]
 impl<T> RangeBounds<T> for RangeFrom<&T> {
     fn start_bound(&self) -> Bound<&T> {