Merge pull request #18746 from lnicola/sync-from-rust

minor: Sync from downstream

23 files changed, 550 insertions, 162 deletions

diff --git a/library/alloc/src/alloc.rs b/library/alloc/src/alloc.rs
index 04b7315e650..ae34fc65326 100644
--- a/library/alloc/src/alloc.rs
+++ b/library/alloc/src/alloc.rs
@@ -10,9 +10,6 @@ use core::hint;
 #[cfg(not(test))]
 use core::ptr::{self, NonNull};
 
-#[cfg(test)]
-mod tests;
-
 extern "Rust" {
     // These are the magic symbols to call the global allocator. rustc generates
     // them to call `__rg_alloc` etc. if there is a `#[global_allocator]` attribute
diff --git a/library/alloc/src/boxed.rs b/library/alloc/src/boxed.rs
index e0f94428cfa..23b85fbd4eb 100644
--- a/library/alloc/src/boxed.rs
+++ b/library/alloc/src/boxed.rs
@@ -1985,7 +1985,8 @@ impl<Args: Tuple, F: Fn<Args> + ?Sized, A: Allocator> Fn<Args> for Box<F, A> {
     }
 }
 
-#[unstable(feature = "async_fn_traits", issue = "none")]
+#[cfg_attr(bootstrap, unstable(feature = "async_closure", issue = "62290"))]
+#[cfg_attr(not(bootstrap), stable(feature = "async_closure", since = "CURRENT_RUSTC_VERSION"))]
 impl<Args: Tuple, F: AsyncFnOnce<Args> + ?Sized, A: Allocator> AsyncFnOnce<Args> for Box<F, A> {
     type Output = F::Output;
     type CallOnceFuture = F::CallOnceFuture;
@@ -1995,7 +1996,8 @@ impl<Args: Tuple, F: AsyncFnOnce<Args> + ?Sized, A: Allocator> AsyncFnOnce<Args>
     }
 }
 
-#[unstable(feature = "async_fn_traits", issue = "none")]
+#[cfg_attr(bootstrap, unstable(feature = "async_closure", issue = "62290"))]
+#[cfg_attr(not(bootstrap), stable(feature = "async_closure", since = "CURRENT_RUSTC_VERSION"))]
 impl<Args: Tuple, F: AsyncFnMut<Args> + ?Sized, A: Allocator> AsyncFnMut<Args> for Box<F, A> {
     type CallRefFuture<'a>
         = F::CallRefFuture<'a>
@@ -2007,7 +2009,8 @@ impl<Args: Tuple, F: AsyncFnMut<Args> + ?Sized, A: Allocator> AsyncFnMut<Args> f
     }
 }
 
-#[unstable(feature = "async_fn_traits", issue = "none")]
+#[cfg_attr(bootstrap, unstable(feature = "async_closure", issue = "62290"))]
+#[cfg_attr(not(bootstrap), stable(feature = "async_closure", since = "CURRENT_RUSTC_VERSION"))]
 impl<Args: Tuple, F: AsyncFn<Args> + ?Sized, A: Allocator> AsyncFn<Args> for Box<F, A> {
     extern "rust-call" fn async_call(&self, args: Args) -> Self::CallRefFuture<'_> {
         F::async_call(self, args)
diff --git a/library/alloc/src/collections/binary_heap/mod.rs b/library/alloc/src/collections/binary_heap/mod.rs
index 5d3997e14e3..965fd63a529 100644
--- a/library/alloc/src/collections/binary_heap/mod.rs
+++ b/library/alloc/src/collections/binary_heap/mod.rs
@@ -155,9 +155,6 @@ use crate::collections::TryReserveError;
 use crate::slice;
 use crate::vec::{self, AsVecIntoIter, Vec};
 
-#[cfg(test)]
-mod tests;
-
 /// A priority queue implemented with a binary heap.
 ///
 /// This will be a max-heap.
@@ -534,8 +531,7 @@ impl<T: Ord, A: Allocator> BinaryHeap<T, A> {
     /// heap.push(1);
     /// heap.push(5);
     /// heap.push(2);
-    /// {
-    ///     let mut val = heap.peek_mut().unwrap();
+    /// if let Some(mut val) = heap.peek_mut() {
     ///     *val = 0;
     /// }
     /// assert_eq!(heap.peek(), Some(&2));
diff --git a/library/alloc/src/collections/linked_list.rs b/library/alloc/src/collections/linked_list.rs
index ca0ea1ec8b2..13168b7a39f 100644
--- a/library/alloc/src/collections/linked_list.rs
+++ b/library/alloc/src/collections/linked_list.rs
@@ -1939,9 +1939,7 @@ pub struct ExtractIf<
     T: 'a,
     F: 'a,
     #[unstable(feature = "allocator_api", issue = "32838")] A: Allocator = Global,
-> where
-    F: FnMut(&mut T) -> bool,
-{
+> {
     list: &'a mut LinkedList<T, A>,
     it: Option<NonNull<Node<T>>>,
     pred: F,
@@ -1979,10 +1977,7 @@ where
 }
 
 #[unstable(feature = "extract_if", reason = "recently added", issue = "43244")]
-impl<T: fmt::Debug, F> fmt::Debug for ExtractIf<'_, T, F>
-where
-    F: FnMut(&mut T) -> bool,
-{
+impl<T: fmt::Debug, F> fmt::Debug for ExtractIf<'_, T, F> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         f.debug_tuple("ExtractIf").field(&self.list).finish()
     }
diff --git a/library/alloc/src/collections/vec_deque/mod.rs b/library/alloc/src/collections/vec_deque/mod.rs
index cf51a84bb6f..0b6a55297e1 100644
--- a/library/alloc/src/collections/vec_deque/mod.rs
+++ b/library/alloc/src/collections/vec_deque/mod.rs
@@ -1869,7 +1869,7 @@ impl<T, A: Allocator> VecDeque<T, A> {
     ///
     /// # Panics
     ///
-    /// Panics if `index` is greater than deque's length
+    /// Panics if `index` is strictly greater than deque's length
     ///
     /// # Examples
     ///
@@ -1884,6 +1884,9 @@ impl<T, A: Allocator> VecDeque<T, A> {
     ///
     /// vec_deque.insert(1, 'd');
     /// assert_eq!(vec_deque, &['a', 'd', 'b', 'c']);
+    ///
+    /// vec_deque.insert(4, 'e');
+    /// assert_eq!(vec_deque, &['a', 'd', 'b', 'c', 'e']);
     /// ```
     #[stable(feature = "deque_extras_15", since = "1.5.0")]
     #[track_caller]
@@ -1928,13 +1931,13 @@ impl<T, A: Allocator> VecDeque<T, A> {
     /// use std::collections::VecDeque;
     ///
     /// let mut buf = VecDeque::new();
-    /// buf.push_back(1);
-    /// buf.push_back(2);
-    /// buf.push_back(3);
-    /// assert_eq!(buf, [1, 2, 3]);
+    /// buf.push_back('a');
+    /// buf.push_back('b');
+    /// buf.push_back('c');
+    /// assert_eq!(buf, ['a', 'b', 'c']);
     ///
-    /// assert_eq!(buf.remove(1), Some(2));
-    /// assert_eq!(buf, [1, 3]);
+    /// assert_eq!(buf.remove(1), Some('b'));
+    /// assert_eq!(buf, ['a', 'c']);
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     #[rustc_confusables("delete", "take")]
@@ -1982,10 +1985,10 @@ impl<T, A: Allocator> VecDeque<T, A> {
     /// ```
     /// use std::collections::VecDeque;
     ///
-    /// let mut buf: VecDeque<_> = [1, 2, 3].into();
+    /// let mut buf: VecDeque<_> = ['a', 'b', 'c'].into();
     /// let buf2 = buf.split_off(1);
-    /// assert_eq!(buf, [1]);
-    /// assert_eq!(buf2, [2, 3]);
+    /// assert_eq!(buf, ['a']);
+    /// assert_eq!(buf2, ['b', 'c']);
     /// ```
     #[inline]
     #[must_use = "use `.truncate()` if you don't need the other half"]
diff --git a/library/alloc/src/ffi/c_str.rs b/library/alloc/src/ffi/c_str.rs
index 9c074383a5e..c7d6d8a55c2 100644
--- a/library/alloc/src/ffi/c_str.rs
+++ b/library/alloc/src/ffi/c_str.rs
@@ -1,8 +1,5 @@
 //! [`CString`] and its related types.
 
-#[cfg(test)]
-mod tests;
-
 use core::borrow::Borrow;
 use core::ffi::{CStr, c_char};
 use core::num::NonZero;
diff --git a/library/alloc/src/lib.rs b/library/alloc/src/lib.rs
index 927c3aa23b9..40759cb0ba8 100644
--- a/library/alloc/src/lib.rs
+++ b/library/alloc/src/lib.rs
@@ -91,6 +91,7 @@
 //
 // Library features:
 // tidy-alphabetical-start
+#![cfg_attr(bootstrap, feature(async_closure))]
 #![cfg_attr(test, feature(str_as_str))]
 #![feature(alloc_layout_extra)]
 #![feature(allocator_api)]
@@ -99,7 +100,6 @@
 #![feature(array_windows)]
 #![feature(ascii_char)]
 #![feature(assert_matches)]
-#![feature(async_closure)]
 #![feature(async_fn_traits)]
 #![feature(async_iterator)]
 #![feature(box_uninit_write)]
@@ -239,8 +239,6 @@ pub mod string;
 pub mod sync;
 #[cfg(all(not(no_global_oom_handling), not(no_rc), not(no_sync)))]
 pub mod task;
-#[cfg(test)]
-mod tests;
 pub mod vec;
 
 #[doc(hidden)]
diff --git a/library/alloc/src/rc.rs b/library/alloc/src/rc.rs
index 7aa1457b1df..b7ec3af9818 100644
--- a/library/alloc/src/rc.rs
+++ b/library/alloc/src/rc.rs
@@ -795,7 +795,7 @@ impl<T, A: Allocator> Rc<T, A> {
         let uninit_ptr: NonNull<_> = (unsafe { &mut *uninit_raw_ptr }).into();
         let init_ptr: NonNull<RcInner<T>> = uninit_ptr.cast();
 
-        let weak = Weak { ptr: init_ptr, alloc: alloc };
+        let weak = Weak { ptr: init_ptr, alloc };
 
         // It's important we don't give up ownership of the weak pointer, or
         // else the memory might be freed by the time `data_fn` returns. If
@@ -2232,12 +2232,20 @@ impl<T: ?Sized, A: Allocator> Deref for Rc<T, A> {
 #[unstable(feature = "pin_coerce_unsized_trait", issue = "123430")]
 unsafe impl<T: ?Sized, A: Allocator> PinCoerceUnsized for Rc<T, A> {}
 
+//#[unstable(feature = "unique_rc_arc", issue = "112566")]
+#[unstable(feature = "pin_coerce_unsized_trait", issue = "123430")]
+unsafe impl<T: ?Sized, A: Allocator> PinCoerceUnsized for UniqueRc<T, A> {}
+
 #[unstable(feature = "pin_coerce_unsized_trait", issue = "123430")]
 unsafe impl<T: ?Sized, A: Allocator> PinCoerceUnsized for Weak<T, A> {}
 
 #[unstable(feature = "deref_pure_trait", issue = "87121")]
 unsafe impl<T: ?Sized, A: Allocator> DerefPure for Rc<T, A> {}
 
+//#[unstable(feature = "unique_rc_arc", issue = "112566")]
+#[unstable(feature = "deref_pure_trait", issue = "87121")]
+unsafe impl<T: ?Sized, A: Allocator> DerefPure for UniqueRc<T, A> {}
+
 #[unstable(feature = "legacy_receiver_trait", issue = "none")]
 impl<T: ?Sized> LegacyReceiver for Rc<T> {}
 
@@ -3684,7 +3692,6 @@ fn data_offset_align(align: usize) -> usize {
 /// previous example, `UniqueRc` allows for more flexibility in the construction of cyclic data,
 /// including fallible or async constructors.
 #[unstable(feature = "unique_rc_arc", issue = "112566")]
-#[derive(Debug)]
 pub struct UniqueRc<
     T: ?Sized,
     #[unstable(feature = "allocator_api", issue = "32838")] A: Allocator = Global,
@@ -3694,12 +3701,253 @@ pub struct UniqueRc<
     alloc: A,
 }
 
+// Not necessary for correctness since `UniqueRc` contains `NonNull`,
+// but having an explicit negative impl is nice for documentation purposes
+// and results in nicer error messages.
+#[unstable(feature = "unique_rc_arc", issue = "112566")]
+impl<T: ?Sized, A: Allocator> !Send for UniqueRc<T, A> {}
+
+// Not necessary for correctness since `UniqueRc` contains `NonNull`,
+// but having an explicit negative impl is nice for documentation purposes
+// and results in nicer error messages.
+#[unstable(feature = "unique_rc_arc", issue = "112566")]
+impl<T: ?Sized, A: Allocator> !Sync for UniqueRc<T, A> {}
+
 #[unstable(feature = "unique_rc_arc", issue = "112566")]
 impl<T: ?Sized + Unsize<U>, U: ?Sized, A: Allocator> CoerceUnsized<UniqueRc<U, A>>
     for UniqueRc<T, A>
 {
 }
 
+//#[unstable(feature = "unique_rc_arc", issue = "112566")]
+#[unstable(feature = "dispatch_from_dyn", issue = "none")]
+impl<T: ?Sized + Unsize<U>, U: ?Sized> DispatchFromDyn<UniqueRc<U>> for UniqueRc<T> {}
+
+#[unstable(feature = "unique_rc_arc", issue = "112566")]
+impl<T: ?Sized + fmt::Display, A: Allocator> fmt::Display for UniqueRc<T, A> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Display::fmt(&**self, f)
+    }
+}
+
+#[unstable(feature = "unique_rc_arc", issue = "112566")]
+impl<T: ?Sized + fmt::Debug, A: Allocator> fmt::Debug for UniqueRc<T, A> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Debug::fmt(&**self, f)
+    }
+}
+
+#[unstable(feature = "unique_rc_arc", issue = "112566")]
+impl<T: ?Sized, A: Allocator> fmt::Pointer for UniqueRc<T, A> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Pointer::fmt(&(&raw const **self), f)
+    }
+}
+
+#[unstable(feature = "unique_rc_arc", issue = "112566")]
+impl<T: ?Sized, A: Allocator> borrow::Borrow<T> for UniqueRc<T, A> {
+    fn borrow(&self) -> &T {
+        &**self
+    }
+}
+
+#[unstable(feature = "unique_rc_arc", issue = "112566")]
+impl<T: ?Sized, A: Allocator> borrow::BorrowMut<T> for UniqueRc<T, A> {
+    fn borrow_mut(&mut self) -> &mut T {
+        &mut **self
+    }
+}
+
+#[unstable(feature = "unique_rc_arc", issue = "112566")]
+impl<T: ?Sized, A: Allocator> AsRef<T> for UniqueRc<T, A> {
+    fn as_ref(&self) -> &T {
+        &**self
+    }
+}
+
+#[unstable(feature = "unique_rc_arc", issue = "112566")]
+impl<T: ?Sized, A: Allocator> AsMut<T> for UniqueRc<T, A> {
+    fn as_mut(&mut self) -> &mut T {
+        &mut **self
+    }
+}
+
+#[unstable(feature = "unique_rc_arc", issue = "112566")]
+impl<T: ?Sized, A: Allocator> Unpin for UniqueRc<T, A> {}
+
+#[unstable(feature = "unique_rc_arc", issue = "112566")]
+impl<T: ?Sized + PartialEq, A: Allocator> PartialEq for UniqueRc<T, A> {
+    /// Equality for two `UniqueRc`s.
+    ///
+    /// Two `UniqueRc`s are equal if their inner values are equal.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(unique_rc_arc)]
+    /// use std::rc::UniqueRc;
+    ///
+    /// let five = UniqueRc::new(5);
+    ///
+    /// assert!(five == UniqueRc::new(5));
+    /// ```
+    #[inline]
+    fn eq(&self, other: &Self) -> bool {
+        PartialEq::eq(&**self, &**other)
+    }
+
+    /// Inequality for two `UniqueRc`s.
+    ///
+    /// Two `UniqueRc`s are not equal if their inner values are not equal.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(unique_rc_arc)]
+    /// use std::rc::UniqueRc;
+    ///
+    /// let five = UniqueRc::new(5);
+    ///
+    /// assert!(five != UniqueRc::new(6));
+    /// ```
+    #[inline]
+    fn ne(&self, other: &Self) -> bool {
+        PartialEq::ne(&**self, &**other)
+    }
+}
+
+#[unstable(feature = "unique_rc_arc", issue = "112566")]
+impl<T: ?Sized + PartialOrd, A: Allocator> PartialOrd for UniqueRc<T, A> {
+    /// Partial comparison for two `UniqueRc`s.
+    ///
+    /// The two are compared by calling `partial_cmp()` on their inner values.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(unique_rc_arc)]
+    /// use std::rc::UniqueRc;
+    /// use std::cmp::Ordering;
+    ///
+    /// let five = UniqueRc::new(5);
+    ///
+    /// assert_eq!(Some(Ordering::Less), five.partial_cmp(&UniqueRc::new(6)));
+    /// ```
+    #[inline(always)]
+    fn partial_cmp(&self, other: &UniqueRc<T, A>) -> Option<Ordering> {
+        (**self).partial_cmp(&**other)
+    }
+
+    /// Less-than comparison for two `UniqueRc`s.
+    ///
+    /// The two are compared by calling `<` on their inner values.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(unique_rc_arc)]
+    /// use std::rc::UniqueRc;
+    ///
+    /// let five = UniqueRc::new(5);
+    ///
+    /// assert!(five < UniqueRc::new(6));
+    /// ```
+    #[inline(always)]
+    fn lt(&self, other: &UniqueRc<T, A>) -> bool {
+        **self < **other
+    }
+
+    /// 'Less than or equal to' comparison for two `UniqueRc`s.
+    ///
+    /// The two are compared by calling `<=` on their inner values.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(unique_rc_arc)]
+    /// use std::rc::UniqueRc;
+    ///
+    /// let five = UniqueRc::new(5);
+    ///
+    /// assert!(five <= UniqueRc::new(5));
+    /// ```
+    #[inline(always)]
+    fn le(&self, other: &UniqueRc<T, A>) -> bool {
+        **self <= **other
+    }
+
+    /// Greater-than comparison for two `UniqueRc`s.
+    ///
+    /// The two are compared by calling `>` on their inner values.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(unique_rc_arc)]
+    /// use std::rc::UniqueRc;
+    ///
+    /// let five = UniqueRc::new(5);
+    ///
+    /// assert!(five > UniqueRc::new(4));
+    /// ```
+    #[inline(always)]
+    fn gt(&self, other: &UniqueRc<T, A>) -> bool {
+        **self > **other
+    }
+
+    /// 'Greater than or equal to' comparison for two `UniqueRc`s.
+    ///
+    /// The two are compared by calling `>=` on their inner values.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(unique_rc_arc)]
+    /// use std::rc::UniqueRc;
+    ///
+    /// let five = UniqueRc::new(5);
+    ///
+    /// assert!(five >= UniqueRc::new(5));
+    /// ```
+    #[inline(always)]
+    fn ge(&self, other: &UniqueRc<T, A>) -> bool {
+        **self >= **other
+    }
+}
+
+#[unstable(feature = "unique_rc_arc", issue = "112566")]
+impl<T: ?Sized + Ord, A: Allocator> Ord for UniqueRc<T, A> {
+    /// Comparison for two `UniqueRc`s.
+    ///
+    /// The two are compared by calling `cmp()` on their inner values.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(unique_rc_arc)]
+    /// use std::rc::UniqueRc;
+    /// use std::cmp::Ordering;
+    ///
+    /// let five = UniqueRc::new(5);
+    ///
+    /// assert_eq!(Ordering::Less, five.cmp(&UniqueRc::new(6)));
+    /// ```
+    #[inline]
+    fn cmp(&self, other: &UniqueRc<T, A>) -> Ordering {
+        (**self).cmp(&**other)
+    }
+}
+
+#[unstable(feature = "unique_rc_arc", issue = "112566")]
+impl<T: ?Sized + Eq, A: Allocator> Eq for UniqueRc<T, A> {}
+
+#[unstable(feature = "unique_rc_arc", issue = "112566")]
+impl<T: ?Sized + Hash, A: Allocator> Hash for UniqueRc<T, A> {
+    fn hash<H: Hasher>(&self, state: &mut H) {
+        (**self).hash(state);
+    }
+}
+
 // Depends on A = Global
 impl<T> UniqueRc<T> {
     /// Creates a new `UniqueRc`.
@@ -3791,9 +4039,6 @@ impl<T: ?Sized, A: Allocator> Deref for UniqueRc<T, A> {
     }
 }
 
-#[unstable(feature = "pin_coerce_unsized_trait", issue = "123430")]
-unsafe impl<T: ?Sized> PinCoerceUnsized for UniqueRc<T> {}
-
 #[unstable(feature = "unique_rc_arc", issue = "112566")]
 impl<T: ?Sized, A: Allocator> DerefMut for UniqueRc<T, A> {
     fn deref_mut(&mut self) -> &mut T {
diff --git a/library/alloc/src/slice.rs b/library/alloc/src/slice.rs
index e3c7835f1d1..edc8d99f2f9 100644
--- a/library/alloc/src/slice.rs
+++ b/library/alloc/src/slice.rs
@@ -27,6 +27,8 @@ pub use core::slice::ArrayChunksMut;
 pub use core::slice::ArrayWindows;
 #[stable(feature = "inherent_ascii_escape", since = "1.60.0")]
 pub use core::slice::EscapeAscii;
+#[unstable(feature = "get_many_mut", issue = "104642")]
+pub use core::slice::GetManyMutError;
 #[stable(feature = "slice_get_slice", since = "1.28.0")]
 pub use core::slice::SliceIndex;
 #[cfg(not(no_global_oom_handling))]
diff --git a/library/alloc/src/string.rs b/library/alloc/src/string.rs
index c5378d78d59..23d060d2158 100644
--- a/library/alloc/src/string.rs
+++ b/library/alloc/src/string.rs
@@ -2675,12 +2675,25 @@ pub trait ToString {
 #[cfg(not(no_global_oom_handling))]
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T: fmt::Display + ?Sized> ToString for T {
+    #[inline]
+    fn to_string(&self) -> String {
+        <Self as SpecToString>::spec_to_string(self)
+    }
+}
+
+#[cfg(not(no_global_oom_handling))]
+trait SpecToString {
+    fn spec_to_string(&self) -> String;
+}
+
+#[cfg(not(no_global_oom_handling))]
+impl<T: fmt::Display + ?Sized> SpecToString for T {
     // A common guideline is to not inline generic functions. However,
     // removing `#[inline]` from this method causes non-negligible regressions.
     // See <https://github.com/rust-lang/rust/pull/74852>, the last attempt
     // to try to remove it.
     #[inline]
-    default fn to_string(&self) -> String {
+    default fn spec_to_string(&self) -> String {
         let mut buf = String::new();
         let mut formatter =
             core::fmt::Formatter::new(&mut buf, core::fmt::FormattingOptions::new());
@@ -2691,42 +2704,34 @@ impl<T: fmt::Display + ?Sized> ToString for T {
     }
 }
 
-#[doc(hidden)]
 #[cfg(not(no_global_oom_handling))]
-#[unstable(feature = "ascii_char", issue = "110998")]
-impl ToString for core::ascii::Char {
+impl SpecToString for core::ascii::Char {
     #[inline]
-    fn to_string(&self) -> String {
+    fn spec_to_string(&self) -> String {
         self.as_str().to_owned()
     }
 }
 
-#[doc(hidden)]
 #[cfg(not(no_global_oom_handling))]
-#[stable(feature = "char_to_string_specialization", since = "1.46.0")]
-impl ToString for char {
+impl SpecToString for char {
     #[inline]
-    fn to_string(&self) -> String {
+    fn spec_to_string(&self) -> String {
         String::from(self.encode_utf8(&mut [0; 4]))
     }
 }
 
-#[doc(hidden)]
 #[cfg(not(no_global_oom_handling))]
-#[stable(feature = "bool_to_string_specialization", since = "1.68.0")]
-impl ToString for bool {
+impl SpecToString for bool {
     #[inline]
-    fn to_string(&self) -> String {
+    fn spec_to_string(&self) -> String {
         String::from(if *self { "true" } else { "false" })
     }
 }
 
-#[doc(hidden)]
 #[cfg(not(no_global_oom_handling))]
-#[stable(feature = "u8_to_string_specialization", since = "1.54.0")]
-impl ToString for u8 {
+impl SpecToString for u8 {
     #[inline]
-    fn to_string(&self) -> String {
+    fn spec_to_string(&self) -> String {
         let mut buf = String::with_capacity(3);
         let mut n = *self;
         if n >= 10 {
@@ -2742,12 +2747,10 @@ impl ToString for u8 {
     }
 }
 
-#[doc(hidden)]
 #[cfg(not(no_global_oom_handling))]
-#[stable(feature = "i8_to_string_specialization", since = "1.54.0")]
-impl ToString for i8 {
+impl SpecToString for i8 {
     #[inline]
-    fn to_string(&self) -> String {
+    fn spec_to_string(&self) -> String {
         let mut buf = String::with_capacity(4);
         if self.is_negative() {
             buf.push('-');
@@ -2788,11 +2791,9 @@ macro_rules! to_string_expr_wrap_in_deref {
 macro_rules! to_string_str {
     {$($($x:ident)*),+} => {
         $(
-            #[doc(hidden)]
-            #[stable(feature = "str_to_string_specialization", since = "1.9.0")]
-            impl ToString for to_string_str_wrap_in_ref!($($x)*) {
+            impl SpecToString for to_string_str_wrap_in_ref!($($x)*) {
                 #[inline]
-                fn to_string(&self) -> String {
+                fn spec_to_string(&self) -> String {
                     String::from(to_string_expr_wrap_in_deref!(self ; $($x)*))
                 }
             }
@@ -2816,32 +2817,26 @@ to_string_str! {
     x,
 }
 
-#[doc(hidden)]
 #[cfg(not(no_global_oom_handling))]
-#[stable(feature = "cow_str_to_string_specialization", since = "1.17.0")]
-impl ToString for Cow<'_, str> {
+impl SpecToString for Cow<'_, str> {
     #[inline]
-    fn to_string(&self) -> String {
+    fn spec_to_string(&self) -> String {
         self[..].to_owned()
     }
 }
 
-#[doc(hidden)]
 #[cfg(not(no_global_oom_handling))]
-#[stable(feature = "string_to_string_specialization", since = "1.17.0")]
-impl ToString for String {
+impl SpecToString for String {
     #[inline]
-    fn to_string(&self) -> String {
+    fn spec_to_string(&self) -> String {
         self.to_owned()
     }
 }
 
-#[doc(hidden)]
 #[cfg(not(no_global_oom_handling))]
-#[stable(feature = "fmt_arguments_to_string_specialization", since = "1.71.0")]
-impl ToString for fmt::Arguments<'_> {
+impl SpecToString for fmt::Arguments<'_> {
     #[inline]
-    fn to_string(&self) -> String {
+    fn spec_to_string(&self) -> String {
         crate::fmt::format(*self)
     }
 }
diff --git a/library/alloc/src/sync.rs b/library/alloc/src/sync.rs
index b8bdd298c27..9be0b3e3e88 100644
--- a/library/alloc/src/sync.rs
+++ b/library/alloc/src/sync.rs
@@ -39,9 +39,6 @@ use crate::string::String;
 #[cfg(not(no_global_oom_handling))]
 use crate::vec::Vec;
 
-#[cfg(test)]
-mod tests;
-
 /// A soft limit on the amount of references that may be made to an `Arc`.
 ///
 /// Going above this limit will abort your program (although not
@@ -787,7 +784,7 @@ impl<T, A: Allocator> Arc<T, A> {
         let uninit_ptr: NonNull<_> = (unsafe { &mut *uninit_raw_ptr }).into();
         let init_ptr: NonNull<ArcInner<T>> = uninit_ptr.cast();
 
-        let weak = Weak { ptr: init_ptr, alloc: alloc };
+        let weak = Weak { ptr: init_ptr, alloc };
 
         // It's important we don't give up ownership of the weak pointer, or
         // else the memory might be freed by the time `data_fn` returns. If
diff --git a/library/alloc/src/vec/extract_if.rs b/library/alloc/src/vec/extract_if.rs
index 72d51e89044..4db13981596 100644
--- a/library/alloc/src/vec/extract_if.rs
+++ b/library/alloc/src/vec/extract_if.rs
@@ -1,3 +1,4 @@
+use core::ops::{Range, RangeBounds};
 use core::{ptr, slice};
 
 use super::Vec;
@@ -14,7 +15,7 @@ use crate::alloc::{Allocator, Global};
 /// #![feature(extract_if)]
 ///
 /// let mut v = vec![0, 1, 2];
-/// let iter: std::vec::ExtractIf<'_, _, _> = v.extract_if(|x| *x % 2 == 0);
+/// let iter: std::vec::ExtractIf<'_, _, _> = v.extract_if(.., |x| *x % 2 == 0);
 /// ```
 #[unstable(feature = "extract_if", reason = "recently added", issue = "43244")]
 #[derive(Debug)]
@@ -24,24 +25,32 @@ pub struct ExtractIf<
     T,
     F,
     #[unstable(feature = "allocator_api", issue = "32838")] A: Allocator = Global,
-> where
-    F: FnMut(&mut T) -> bool,
-{
-    pub(super) vec: &'a mut Vec<T, A>,
+> {
+    vec: &'a mut Vec<T, A>,
     /// The index of the item that will be inspected by the next call to `next`.
-    pub(super) idx: usize,
+    idx: usize,
+    /// Elements at and beyond this point will be retained. Must be equal or smaller than `old_len`.
+    end: usize,
     /// The number of items that have been drained (removed) thus far.
-    pub(super) del: usize,
+    del: usize,
     /// The original length of `vec` prior to draining.
-    pub(super) old_len: usize,
+    old_len: usize,
     /// The filter test predicate.
-    pub(super) pred: F,
+    pred: F,
 }
 
-impl<T, F, A: Allocator> ExtractIf<'_, T, F, A>
-where
-    F: FnMut(&mut T) -> bool,
-{
+impl<'a, T, F, A: Allocator> ExtractIf<'a, T, F, A> {
+    pub(super) fn new<R: RangeBounds<usize>>(vec: &'a mut Vec<T, A>, pred: F, range: R) -> Self {
+        let old_len = vec.len();
+        let Range { start, end } = slice::range(range, ..old_len);
+
+        // Guard against the vec getting leaked (leak amplification)
+        unsafe {
+            vec.set_len(0);
+        }
+        ExtractIf { vec, idx: start, del: 0, end, old_len, pred }
+    }
+
     /// Returns a reference to the underlying allocator.
     #[unstable(feature = "allocator_api", issue = "32838")]
     #[inline]
@@ -59,7 +68,7 @@ where
 
     fn next(&mut self) -> Option<T> {
         unsafe {
-            while self.idx < self.old_len {
+            while self.idx < self.end {
                 let i = self.idx;
                 let v = slice::from_raw_parts_mut(self.vec.as_mut_ptr(), self.old_len);
                 let drained = (self.pred)(&mut v[i]);
@@ -82,24 +91,15 @@ where
     }
 
     fn size_hint(&self) -> (usize, Option<usize>) {
-        (0, Some(self.old_len - self.idx))
+        (0, Some(self.end - self.idx))
     }
 }
 
 #[unstable(feature = "extract_if", reason = "recently added", issue = "43244")]
-impl<T, F, A: Allocator> Drop for ExtractIf<'_, T, F, A>
-where
-    F: FnMut(&mut T) -> bool,
-{
+impl<T, F, A: Allocator> Drop for ExtractIf<'_, T, F, A> {
     fn drop(&mut self) {
         unsafe {
             if self.idx < self.old_len && self.del > 0 {
-                // This is a pretty messed up state, and there isn't really an
-                // obviously right thing to do. We don't want to keep trying
-                // to execute `pred`, so we just backshift all the unprocessed
-                // elements and tell the vec that they still exist. The backshift
-                // is required to prevent a double-drop of the last successfully
-                // drained item prior to a panic in the predicate.
                 let ptr = self.vec.as_mut_ptr();
                 let src = ptr.add(self.idx);
                 let dst = src.sub(self.del);
diff --git a/library/alloc/src/vec/mod.rs b/library/alloc/src/vec/mod.rs
index 457be3ae77f..3a706d5f36b 100644
--- a/library/alloc/src/vec/mod.rs
+++ b/library/alloc/src/vec/mod.rs
@@ -56,7 +56,6 @@
 #[cfg(not(no_global_oom_handling))]
 use core::cmp;
 use core::cmp::Ordering;
-use core::fmt;
 use core::hash::{Hash, Hasher};
 #[cfg(not(no_global_oom_handling))]
 use core::iter;
@@ -65,6 +64,7 @@ use core::mem::{self, ManuallyDrop, MaybeUninit, SizedTypeProperties};
 use core::ops::{self, Index, IndexMut, Range, RangeBounds};
 use core::ptr::{self, NonNull};
 use core::slice::{self, SliceIndex};
+use core::{fmt, intrinsics};
 
 #[unstable(feature = "extract_if", reason = "recently added", issue = "43244")]
 pub use self::extract_if::ExtractIf;
@@ -1824,7 +1824,10 @@ impl<T, A: Allocator> Vec<T, A> {
     ///
     /// # Examples
     ///
-    /// This method can be useful for situations in which the vector
+    /// See [`spare_capacity_mut()`] for an example with safe
+    /// initialization of capacity elements and use of this method.
+    ///
+    /// `set_len()` can be useful for situations in which the vector
     /// is serving as a buffer for other code, particularly over FFI:
     ///
     /// ```no_run
@@ -1884,6 +1887,8 @@ impl<T, A: Allocator> Vec<T, A> {
     ///
     /// Normally, here, one would use [`clear`] instead to correctly drop
     /// the contents and thus not leak memory.
+    ///
+    /// [`spare_capacity_mut()`]: Vec::spare_capacity_mut
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     pub unsafe fn set_len(&mut self, new_len: usize) {
@@ -1953,11 +1958,11 @@ impl<T, A: Allocator> Vec<T, A> {
     /// # Examples
     ///
     /// ```
-    /// let mut vec = vec![1, 2, 3];
-    /// vec.insert(1, 4);
-    /// assert_eq!(vec, [1, 4, 2, 3]);
-    /// vec.insert(4, 5);
-    /// assert_eq!(vec, [1, 4, 2, 3, 5]);
+    /// let mut vec = vec!['a', 'b', 'c'];
+    /// vec.insert(1, 'd');
+    /// assert_eq!(vec, ['a', 'd', 'b', 'c']);
+    /// vec.insert(4, 'e');
+    /// assert_eq!(vec, ['a', 'd', 'b', 'c', 'e']);
     /// ```
     ///
     /// # Time complexity
@@ -2024,9 +2029,9 @@ impl<T, A: Allocator> Vec<T, A> {
     /// # Examples
     ///
     /// ```
-    /// let mut v = vec![1, 2, 3];
-    /// assert_eq!(v.remove(1), 2);
-    /// assert_eq!(v, [1, 3]);
+    /// let mut v = vec!['a', 'b', 'c'];
+    /// assert_eq!(v.remove(1), 'b');
+    /// assert_eq!(v, ['a', 'c']);
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     #[track_caller]
@@ -2675,7 +2680,14 @@ impl<T, A: Allocator> Vec<T, A> {
     #[rustc_const_unstable(feature = "const_vec_string_slice", issue = "129041")]
     #[rustc_confusables("length", "size")]
     pub const fn len(&self) -> usize {
-        self.len
+        let len = self.len;
+
+        // SAFETY: The maximum capacity of `Vec<T>` is `isize::MAX` bytes, so the maximum value can
+        // be returned is `usize::checked_div(mem::size_of::<T>()).unwrap_or(usize::MAX)`, which
+        // matches the definition of `T::MAX_SLICE_LEN`.
+        unsafe { intrinsics::assume(len <= T::MAX_SLICE_LEN) };
+
+        len
     }
 
     /// Returns `true` if the vector contains no elements.
@@ -2715,10 +2727,10 @@ impl<T, A: Allocator> Vec<T, A> {
     /// # Examples
     ///
     /// ```
-    /// let mut vec = vec![1, 2, 3];
+    /// let mut vec = vec!['a', 'b', 'c'];
     /// let vec2 = vec.split_off(1);
-    /// assert_eq!(vec, [1]);
-    /// assert_eq!(vec2, [2, 3]);
+    /// assert_eq!(vec, ['a']);
+    /// assert_eq!(vec2, ['b', 'c']);
     /// ```
     #[cfg(not(no_global_oom_handling))]
     #[inline]
@@ -2982,9 +2994,9 @@ impl<T: Clone, A: Allocator> Vec<T, A> {
     /// vec.resize(3, "world");
     /// assert_eq!(vec, ["hello", "world", "world"]);
     ///
-    /// let mut vec = vec![1, 2, 3, 4];
-    /// vec.resize(2, 0);
-    /// assert_eq!(vec, [1, 2]);
+    /// let mut vec = vec!['a', 'b', 'c', 'd'];
+    /// vec.resize(2, '_');
+    /// assert_eq!(vec, ['a', 'b']);
     /// ```
     #[cfg(not(no_global_oom_handling))]
     #[stable(feature = "vec_resize", since = "1.5.0")]
@@ -3615,12 +3627,15 @@ impl<T, A: Allocator> Vec<T, A> {
         Splice { drain: self.drain(range), replace_with: replace_with.into_iter() }
     }
 
-    /// Creates an iterator which uses a closure to determine if an element should be removed.
+    /// Creates an iterator which uses a closure to determine if element in the range should be removed.
     ///
     /// If the closure returns true, then the element is removed and yielded.
     /// If the closure returns false, the element will remain in the vector and will not be yielded
     /// by the iterator.
     ///
+    /// Only elements that fall in the provided range are considered for extraction, but any elements
+    /// after the range will still have to be moved if any element has been extracted.
+    ///
     /// If the returned `ExtractIf` is not exhausted, e.g. because it is dropped without iterating
     /// or the iteration short-circuits, then the remaining elements will be retained.
     /// Use [`retain`] with a negated predicate if you do not need the returned iterator.
@@ -3630,10 +3645,12 @@ impl<T, A: Allocator> Vec<T, A> {
     /// Using this method is equivalent to the following code:
     ///
     /// ```
+    /// # use std::cmp::min;
     /// # let some_predicate = |x: &mut i32| { *x == 2 || *x == 3 || *x == 6 };
     /// # let mut vec = vec![1, 2, 3, 4, 5, 6];
-    /// let mut i = 0;
-    /// while i < vec.len() {
+    /// # let range = 1..4;
+    /// let mut i = range.start;
+    /// while i < min(vec.len(), range.end) {
     ///     if some_predicate(&mut vec[i]) {
     ///         let val = vec.remove(i);
     ///         // your code here
@@ -3648,8 +3665,12 @@ impl<T, A: Allocator> Vec<T, A> {
     /// But `extract_if` is easier to use. `extract_if` is also more efficient,
     /// because it can backshift the elements of the array in bulk.
     ///
-    /// Note that `extract_if` also lets you mutate every element in the filter closure,
-    /// regardless of whether you choose to keep or remove it.
+    /// Note that `extract_if` also lets you mutate the elements passed to the filter closure,
+    /// regardless of whether you choose to keep or remove them.
+    ///
+    /// # Panics
+    ///
+    /// If `range` is out of bounds.
     ///
     /// # Examples
     ///
@@ -3659,25 +3680,29 @@ impl<T, A: Allocator> Vec<T, A> {
     /// #![feature(extract_if)]
     /// let mut numbers = vec![1, 2, 3, 4, 5, 6, 8, 9, 11, 13, 14, 15];
     ///
-    /// let evens = numbers.extract_if(|x| *x % 2 == 0).collect::<Vec<_>>();
+    /// let evens = numbers.extract_if(.., |x| *x % 2 == 0).collect::<Vec<_>>();
     /// let odds = numbers;
     ///
     /// assert_eq!(evens, vec![2, 4, 6, 8, 14]);
     /// assert_eq!(odds, vec![1, 3, 5, 9, 11, 13, 15]);
     /// ```
+    ///
+    /// Using the range argument to only process a part of the vector:
+    ///
+    /// ```
+    /// #![feature(extract_if)]
+    /// let mut items = vec![0, 0, 0, 0, 0, 0, 0, 1, 2, 1, 2, 1, 2];
+    /// let ones = items.extract_if(7.., |x| *x == 1).collect::<Vec<_>>();
+    /// assert_eq!(items, vec![0, 0, 0, 0, 0, 0, 0, 2, 2, 2]);
+    /// assert_eq!(ones.len(), 3);
+    /// ```
     #[unstable(feature = "extract_if", reason = "recently added", issue = "43244")]
-    pub fn extract_if<F>(&mut self, filter: F) -> ExtractIf<'_, T, F, A>
+    pub fn extract_if<F, R>(&mut self, range: R, filter: F) -> ExtractIf<'_, T, F, A>
     where
         F: FnMut(&mut T) -> bool,
+        R: RangeBounds<usize>,
     {
-        let old_len = self.len();
-
-        // Guard against us getting leaked (leak amplification)
-        unsafe {
-            self.set_len(0);
-        }
-
-        ExtractIf { vec: self, idx: 0, del: 0, old_len, pred: filter }
+        ExtractIf::new(self, filter, range)
     }
 }
 
diff --git a/library/alloc/src/alloc/tests.rs b/library/alloc/tests/alloc.rs
index 5d6077f057a..1e722d66795 100644
--- a/library/alloc/src/alloc/tests.rs
+++ b/library/alloc/tests/alloc.rs
@@ -1,10 +1,9 @@
-use super::*;
+use alloc::alloc::*;
+use alloc::boxed::Box;
 
 extern crate test;
 use test::Bencher;
 
-use crate::boxed::Box;
-
 #[test]
 fn allocate_zeroed() {
     unsafe {
diff --git a/library/alloc/src/ffi/c_str/tests.rs b/library/alloc/tests/c_str2.rs
index d6b797347c2..0f4c27fa123 100644
--- a/library/alloc/src/ffi/c_str/tests.rs
+++ b/library/alloc/tests/c_str2.rs
@@ -1,11 +1,12 @@
+use alloc::ffi::CString;
+use alloc::rc::Rc;
+use alloc::sync::Arc;
 use core::assert_matches::assert_matches;
-use core::ffi::FromBytesUntilNulError;
+use core::ffi::{CStr, FromBytesUntilNulError, c_char};
 #[allow(deprecated)]
 use core::hash::SipHasher13 as DefaultHasher;
 use core::hash::{Hash, Hasher};
 
-use super::*;
-
 #[test]
 fn c_to_rust() {
     let data = b"123\0";
diff --git a/library/alloc/src/collections/binary_heap/tests.rs b/library/alloc/tests/collections/binary_heap.rs
index ad0a020a1a9..55405ffe8c4 100644
--- a/library/alloc/src/collections/binary_heap/tests.rs
+++ b/library/alloc/tests/collections/binary_heap.rs
@@ -1,7 +1,9 @@
+use alloc::boxed::Box;
+use alloc::collections::binary_heap::*;
+use std::iter::TrustedLen;
+use std::mem;
 use std::panic::{AssertUnwindSafe, catch_unwind};
 
-use super::*;
-use crate::boxed::Box;
 use crate::testing::crash_test::{CrashTestDummy, Panic};
 
 #[test]
@@ -531,7 +533,7 @@ fn panic_safe() {
             self.0.partial_cmp(&other.0)
         }
     }
-    let mut rng = crate::test_helpers::test_rng();
+    let mut rng = crate::test_rng();
     const DATASZ: usize = 32;
     // Miri is too slow
     let ntest = if cfg!(miri) { 1 } else { 10 };
diff --git a/library/alloc/tests/collections/mod.rs b/library/alloc/tests/collections/mod.rs
new file mode 100644
index 00000000000..e73f3aaef8c
--- /dev/null
+++ b/library/alloc/tests/collections/mod.rs
@@ -0,0 +1 @@
+mod binary_heap;
diff --git a/library/alloc/tests/lib.rs b/library/alloc/tests/lib.rs
index bcab17e7b2d..393bdfe48b7 100644
--- a/library/alloc/tests/lib.rs
+++ b/library/alloc/tests/lib.rs
@@ -5,8 +5,10 @@
 #![feature(btree_extract_if)]
 #![feature(cow_is_borrowed)]
 #![feature(core_intrinsics)]
+#![feature(downcast_unchecked)]
 #![feature(extract_if)]
 #![feature(exact_size_is_empty)]
+#![feature(hashmap_internals)]
 #![feature(linked_list_cursors)]
 #![feature(map_try_insert)]
 #![feature(pattern)]
@@ -29,9 +31,11 @@
 #![feature(const_str_from_utf8)]
 #![feature(panic_update_hook)]
 #![feature(pointer_is_aligned_to)]
+#![feature(test)]
 #![feature(thin_box)]
 #![feature(drain_keep_rest)]
 #![feature(local_waker)]
+#![feature(str_as_str)]
 #![feature(strict_provenance_lints)]
 #![feature(vec_pop_if)]
 #![feature(unique_rc_arc)]
@@ -40,25 +44,33 @@
 #![deny(fuzzy_provenance_casts)]
 #![deny(unsafe_op_in_unsafe_fn)]
 
+extern crate test;
+
 use std::hash::{DefaultHasher, Hash, Hasher};
 
+mod alloc;
 mod arc;
 mod autotraits;
 mod borrow;
 mod boxed;
 mod btree_set_hash;
 mod c_str;
+mod c_str2;
+mod collections;
 mod const_fns;
 mod cow_str;
 mod fmt;
 mod heap;
 mod linked_list;
+mod misc_tests;
 mod rc;
 mod slice;
 mod sort;
 mod str;
 mod string;
+mod sync;
 mod task;
+mod testing;
 mod thin_box;
 mod vec;
 mod vec_deque;
@@ -69,6 +81,18 @@ fn hash<T: Hash>(t: &T) -> u64 {
     s.finish()
 }
 
+/// Copied from `std::test_helpers::test_rng`, since these tests rely on the
+/// seed not being the same for every RNG invocation too.
+fn test_rng() -> rand_xorshift::XorShiftRng {
+    use std::hash::{BuildHasher, Hash, Hasher};
+    let mut hasher = std::hash::RandomState::new().build_hasher();
+    std::panic::Location::caller().hash(&mut hasher);
+    let hc64 = hasher.finish();
+    let seed_vec = hc64.to_le_bytes().into_iter().chain(0u8..8).collect::<Vec<u8>>();
+    let seed: [u8; 16] = seed_vec.as_slice().try_into().unwrap();
+    rand::SeedableRng::from_seed(seed)
+}
+
 // FIXME: Instantiated functions with i128 in the signature is not supported in Emscripten.
 // See https://github.com/kripken/emscripten-fastcomp/issues/169
 #[cfg(not(target_os = "emscripten"))]
diff --git a/library/alloc/src/tests.rs b/library/alloc/tests/misc_tests.rs
index b95d11cb07e..b95d11cb07e 100644
--- a/library/alloc/src/tests.rs
+++ b/library/alloc/tests/misc_tests.rs
diff --git a/library/alloc/src/sync/tests.rs b/library/alloc/tests/sync.rs
index de5816fda97..7a9a4abfdc6 100644
--- a/library/alloc/src/sync/tests.rs
+++ b/library/alloc/tests/sync.rs
@@ -1,14 +1,16 @@
+use alloc::sync::*;
+use std::alloc::{AllocError, Allocator, Layout};
+use std::any::Any;
 use std::clone::Clone;
 use std::mem::MaybeUninit;
 use std::option::Option::None;
+use std::ptr::NonNull;
 use std::sync::Mutex;
-use std::sync::atomic::AtomicUsize;
-use std::sync::atomic::Ordering::SeqCst;
+use std::sync::atomic::Ordering::*;
+use std::sync::atomic::{self, AtomicUsize};
 use std::sync::mpsc::channel;
 use std::thread;
 
-use super::*;
-
 struct Canary(*mut AtomicUsize);
 
 impl Drop for Canary {
diff --git a/library/alloc/tests/testing/crash_test.rs b/library/alloc/tests/testing/crash_test.rs
new file mode 100644
index 00000000000..502fe6c10c6
--- /dev/null
+++ b/library/alloc/tests/testing/crash_test.rs
@@ -0,0 +1,80 @@
+use std::cmp::Ordering;
+use std::fmt::Debug;
+use std::sync::atomic::AtomicUsize;
+use std::sync::atomic::Ordering::SeqCst;
+
+/// A blueprint for crash test dummy instances that monitor drops.
+/// Some instances may be configured to panic at some point.
+///
+/// Crash test dummies are identified and ordered by an id, so they can be used
+/// as keys in a BTreeMap.
+#[derive(Debug)]
+pub struct CrashTestDummy {
+    pub id: usize,
+    dropped: AtomicUsize,
+}
+
+impl CrashTestDummy {
+    /// Creates a crash test dummy design. The `id` determines order and equality of instances.
+    pub fn new(id: usize) -> CrashTestDummy {
+        CrashTestDummy { id, dropped: AtomicUsize::new(0) }
+    }
+
+    /// Creates an instance of a crash test dummy that records what events it experiences
+    /// and optionally panics.
+    pub fn spawn(&self, panic: Panic) -> Instance<'_> {
+        Instance { origin: self, panic }
+    }
+
+    /// Returns how many times instances of the dummy have been dropped.
+    pub fn dropped(&self) -> usize {
+        self.dropped.load(SeqCst)
+    }
+}
+
+#[derive(Debug)]
+pub struct Instance<'a> {
+    origin: &'a CrashTestDummy,
+    panic: Panic,
+}
+
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub enum Panic {
+    Never,
+    InDrop,
+}
+
+impl Instance<'_> {
+    pub fn id(&self) -> usize {
+        self.origin.id
+    }
+}
+
+impl Drop for Instance<'_> {
+    fn drop(&mut self) {
+        self.origin.dropped.fetch_add(1, SeqCst);
+        if self.panic == Panic::InDrop {
+            panic!("panic in `drop`");
+        }
+    }
+}
+
+impl PartialOrd for Instance<'_> {
+    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+        self.id().partial_cmp(&other.id())
+    }
+}
+
+impl Ord for Instance<'_> {
+    fn cmp(&self, other: &Self) -> Ordering {
+        self.id().cmp(&other.id())
+    }
+}
+
+impl PartialEq for Instance<'_> {
+    fn eq(&self, other: &Self) -> bool {
+        self.id().eq(&other.id())
+    }
+}
+
+impl Eq for Instance<'_> {}
diff --git a/library/alloc/tests/testing/mod.rs b/library/alloc/tests/testing/mod.rs
new file mode 100644
index 00000000000..0a3dd191dc8
--- /dev/null
+++ b/library/alloc/tests/testing/mod.rs
@@ -0,0 +1 @@
+pub mod crash_test;
diff --git a/library/alloc/tests/vec.rs b/library/alloc/tests/vec.rs
index 0f27fdff3e1..84679827ba1 100644
--- a/library/alloc/tests/vec.rs
+++ b/library/alloc/tests/vec.rs
@@ -1414,7 +1414,7 @@ fn extract_if_empty() {
     let mut vec: Vec<i32> = vec![];
 
     {
-        let mut iter = vec.extract_if(|_| true);
+        let mut iter = vec.extract_if(.., |_| true);
         assert_eq!(iter.size_hint(), (0, Some(0)));
         assert_eq!(iter.next(), None);
         assert_eq!(iter.size_hint(), (0, Some(0)));
@@ -1431,7 +1431,7 @@ fn extract_if_zst() {
     let initial_len = vec.len();
     let mut count = 0;
     {
-        let mut iter = vec.extract_if(|_| true);
+        let mut iter = vec.extract_if(.., |_| true);
         assert_eq!(iter.size_hint(), (0, Some(initial_len)));
         while let Some(_) = iter.next() {
             count += 1;
@@ -1454,7 +1454,7 @@ fn extract_if_false() {
     let initial_len = vec.len();
     let mut count = 0;
     {
-        let mut iter = vec.extract_if(|_| false);
+        let mut iter = vec.extract_if(.., |_| false);
         assert_eq!(iter.size_hint(), (0, Some(initial_len)));
         for _ in iter.by_ref() {
             count += 1;
@@ -1476,7 +1476,7 @@ fn extract_if_true() {
     let initial_len = vec.len();
     let mut count = 0;
     {
-        let mut iter = vec.extract_if(|_| true);
+        let mut iter = vec.extract_if(.., |_| true);
         assert_eq!(iter.size_hint(), (0, Some(initial_len)));
         while let Some(_) = iter.next() {
             count += 1;
@@ -1493,6 +1493,31 @@ fn extract_if_true() {
 }
 
 #[test]
+fn extract_if_ranges() {
+    let mut vec = vec![0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
+
+    let mut count = 0;
+    let it = vec.extract_if(1..=3, |_| {
+        count += 1;
+        true
+    });
+    assert_eq!(it.collect::<Vec<_>>(), vec![1, 2, 3]);
+    assert_eq!(vec, vec![0, 4, 5, 6, 7, 8, 9, 10]);
+    assert_eq!(count, 3);
+
+    let it = vec.extract_if(1..=3, |_| false);
+    assert_eq!(it.collect::<Vec<_>>(), vec![]);
+    assert_eq!(vec, vec![0, 4, 5, 6, 7, 8, 9, 10]);
+}
+
+#[test]
+#[should_panic]
+fn extract_if_out_of_bounds() {
+    let mut vec = vec![0, 1];
+    let _ = vec.extract_if(5.., |_| true).for_each(drop);
+}
+
+#[test]
 fn extract_if_complex() {
     {
         //                [+xxx++++++xxxxx++++x+x++]
@@ -1501,7 +1526,7 @@ fn extract_if_complex() {
             39,
         ];
 
-        let removed = vec.extract_if(|x| *x % 2 == 0).collect::<Vec<_>>();
+        let removed = vec.extract_if(.., |x| *x % 2 == 0).collect::<Vec<_>>();
         assert_eq!(removed.len(), 10);
         assert_eq!(removed, vec![2, 4, 6, 18, 20, 22, 24, 26, 34, 36]);
 
@@ -1515,7 +1540,7 @@ fn extract_if_complex() {
             2, 4, 6, 7, 9, 11, 13, 15, 17, 18, 20, 22, 24, 26, 27, 29, 31, 33, 34, 35, 36, 37, 39,
         ];
 
-        let removed = vec.extract_if(|x| *x % 2 == 0).collect::<Vec<_>>();
+        let removed = vec.extract_if(.., |x| *x % 2 == 0).collect::<Vec<_>>();
         assert_eq!(removed.len(), 10);
         assert_eq!(removed, vec![2, 4, 6, 18, 20, 22, 24, 26, 34, 36]);
 
@@ -1528,7 +1553,7 @@ fn extract_if_complex() {
         let mut vec =
             vec![2, 4, 6, 7, 9, 11, 13, 15, 17, 18, 20, 22, 24, 26, 27, 29, 31, 33, 34, 35, 36];
 
-        let removed = vec.extract_if(|x| *x % 2 == 0).collect::<Vec<_>>();
+        let removed = vec.extract_if(.., |x| *x % 2 == 0).collect::<Vec<_>>();
         assert_eq!(removed.len(), 10);
         assert_eq!(removed, vec![2, 4, 6, 18, 20, 22, 24, 26, 34, 36]);
 
@@ -1540,7 +1565,7 @@ fn extract_if_complex() {
         //                [xxxxxxxxxx+++++++++++]
         let mut vec = vec![2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 1, 3, 5, 7, 9, 11, 13, 15, 17, 19];
 
-        let removed = vec.extract_if(|x| *x % 2 == 0).collect::<Vec<_>>();
+        let removed = vec.extract_if(.., |x| *x % 2 == 0).collect::<Vec<_>>();
         assert_eq!(removed.len(), 10);
         assert_eq!(removed, vec![2, 4, 6, 8, 10, 12, 14, 16, 18, 20]);
 
@@ -1552,7 +1577,7 @@ fn extract_if_complex() {
         //                [+++++++++++xxxxxxxxxx]
         let mut vec = vec![1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20];
 
-        let removed = vec.extract_if(|x| *x % 2 == 0).collect::<Vec<_>>();
+        let removed = vec.extract_if(.., |x| *x % 2 == 0).collect::<Vec<_>>();
         assert_eq!(removed.len(), 10);
         assert_eq!(removed, vec![2, 4, 6, 8, 10, 12, 14, 16, 18, 20]);
 
@@ -1600,7 +1625,7 @@ fn extract_if_consumed_panic() {
             }
             c.index < 6
         };
-        let drain = data.extract_if(filter);
+        let drain = data.extract_if(.., filter);
 
         // NOTE: The ExtractIf is explicitly consumed
         drain.for_each(drop);
@@ -1653,7 +1678,7 @@ fn extract_if_unconsumed_panic() {
             }
             c.index < 6
         };
-        let _drain = data.extract_if(filter);
+        let _drain = data.extract_if(.., filter);
 
         // NOTE: The ExtractIf is dropped without being consumed
     });
@@ -1669,7 +1694,7 @@ fn extract_if_unconsumed_panic() {
 #[test]
 fn extract_if_unconsumed() {
     let mut vec = vec![1, 2, 3, 4];
-    let drain = vec.extract_if(|&mut x| x % 2 != 0);
+    let drain = vec.extract_if(.., |&mut x| x % 2 != 0);
     drop(drain);
     assert_eq!(vec, [1, 2, 3, 4]);
 }