18 files changed, 242 insertions, 105 deletions

diff --git a/library/std/src/collections/hash/map.rs b/library/std/src/collections/hash/map.rs
index c722bad2e4f..f3316d97c5f 100644
--- a/library/std/src/collections/hash/map.rs
+++ b/library/std/src/collections/hash/map.rs
@@ -623,28 +623,27 @@ impl<K, V, S> HashMap<K, V, S> {
     /// If the closure returns false, or panics, the element remains in the map and will not be
     /// yielded.
     ///
-    /// Note that `drain_filter` lets you mutate every value in the filter closure, regardless of
+    /// Note that `extract_if` lets you mutate every value in the filter closure, regardless of
     /// whether you choose to keep or remove it.
     ///
-    /// If the iterator is only partially consumed or not consumed at all, each of the remaining
-    /// elements will still be subjected to the closure and removed and dropped if it returns true.
+    /// 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.
     ///
-    /// It is unspecified how many more elements will be subjected to the closure
-    /// if a panic occurs in the closure, or a panic occurs while dropping an element,
-    /// or if the `DrainFilter` value is leaked.
+    /// [`retain`]: HashMap::retain
     ///
     /// # Examples
     ///
     /// Splitting a map into even and odd keys, reusing the original map:
     ///
     /// ```
-    /// #![feature(hash_drain_filter)]
+    /// #![feature(hash_extract_if)]
     /// use std::collections::HashMap;
     ///
     /// let mut map: HashMap<i32, i32> = (0..8).map(|x| (x, x)).collect();
-    /// let drained: HashMap<i32, i32> = map.drain_filter(|k, _v| k % 2 == 0).collect();
+    /// let extracted: HashMap<i32, i32> = map.extract_if(|k, _v| k % 2 == 0).collect();
     ///
-    /// let mut evens = drained.keys().copied().collect::<Vec<_>>();
+    /// let mut evens = extracted.keys().copied().collect::<Vec<_>>();
     /// let mut odds = map.keys().copied().collect::<Vec<_>>();
     /// evens.sort();
     /// odds.sort();
@@ -654,12 +653,12 @@ impl<K, V, S> HashMap<K, V, S> {
     /// ```
     #[inline]
     #[rustc_lint_query_instability]
-    #[unstable(feature = "hash_drain_filter", issue = "59618")]
-    pub fn drain_filter<F>(&mut self, pred: F) -> DrainFilter<'_, K, V, F>
+    #[unstable(feature = "hash_extract_if", issue = "59618")]
+    pub fn extract_if<F>(&mut self, pred: F) -> ExtractIf<'_, K, V, F>
     where
         F: FnMut(&K, &mut V) -> bool,
     {
-        DrainFilter { base: self.base.drain_filter(pred) }
+        ExtractIf { base: self.base.extract_if(pred) }
     }
 
     /// Retains only the elements specified by the predicate.
@@ -1578,28 +1577,29 @@ impl<'a, K, V> Drain<'a, K, V> {
 
 /// A draining, filtering iterator over the entries of a `HashMap`.
 ///
-/// This `struct` is created by the [`drain_filter`] method on [`HashMap`].
+/// This `struct` is created by the [`extract_if`] method on [`HashMap`].
 ///
-/// [`drain_filter`]: HashMap::drain_filter
+/// [`extract_if`]: HashMap::extract_if
 ///
 /// # Example
 ///
 /// ```
-/// #![feature(hash_drain_filter)]
+/// #![feature(hash_extract_if)]
 ///
 /// use std::collections::HashMap;
 ///
 /// let mut map = HashMap::from([
 ///     ("a", 1),
 /// ]);
-/// let iter = map.drain_filter(|_k, v| *v % 2 == 0);
+/// let iter = map.extract_if(|_k, v| *v % 2 == 0);
 /// ```
-#[unstable(feature = "hash_drain_filter", issue = "59618")]
-pub struct DrainFilter<'a, K, V, F>
+#[unstable(feature = "hash_extract_if", issue = "59618")]
+#[must_use = "iterators are lazy and do nothing unless consumed"]
+pub struct ExtractIf<'a, K, V, F>
 where
     F: FnMut(&K, &mut V) -> bool,
 {
-    base: base::DrainFilter<'a, K, V, F>,
+    base: base::ExtractIf<'a, K, V, F>,
 }
 
 /// A mutable iterator over the values of a `HashMap`.
@@ -2479,8 +2479,8 @@ where
     }
 }
 
-#[unstable(feature = "hash_drain_filter", issue = "59618")]
-impl<K, V, F> Iterator for DrainFilter<'_, K, V, F>
+#[unstable(feature = "hash_extract_if", issue = "59618")]
+impl<K, V, F> Iterator for ExtractIf<'_, K, V, F>
 where
     F: FnMut(&K, &mut V) -> bool,
 {
@@ -2496,16 +2496,16 @@ where
     }
 }
 
-#[unstable(feature = "hash_drain_filter", issue = "59618")]
-impl<K, V, F> FusedIterator for DrainFilter<'_, K, V, F> where F: FnMut(&K, &mut V) -> bool {}
+#[unstable(feature = "hash_extract_if", issue = "59618")]
+impl<K, V, F> FusedIterator for ExtractIf<'_, K, V, F> where F: FnMut(&K, &mut V) -> bool {}
 
-#[unstable(feature = "hash_drain_filter", issue = "59618")]
-impl<'a, K, V, F> fmt::Debug for DrainFilter<'a, K, V, F>
+#[unstable(feature = "hash_extract_if", issue = "59618")]
+impl<'a, K, V, F> fmt::Debug for ExtractIf<'a, K, V, F>
 where
     F: FnMut(&K, &mut V) -> bool,
 {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        f.debug_struct("DrainFilter").finish_non_exhaustive()
+        f.debug_struct("ExtractIf").finish_non_exhaustive()
     }
 }
 
diff --git a/library/std/src/collections/hash/map/tests.rs b/library/std/src/collections/hash/map/tests.rs
index 6b89518e2e2..91a3776e7be 100644
--- a/library/std/src/collections/hash/map/tests.rs
+++ b/library/std/src/collections/hash/map/tests.rs
@@ -944,7 +944,7 @@ fn test_raw_entry() {
     }
 }
 
-mod test_drain_filter {
+mod test_extract_if {
     use super::*;
 
     use crate::panic::{catch_unwind, AssertUnwindSafe};
@@ -968,7 +968,7 @@ mod test_drain_filter {
     #[test]
     fn empty() {
         let mut map: HashMap<i32, i32> = HashMap::new();
-        map.drain_filter(|_, _| unreachable!("there's nothing to decide on"));
+        map.extract_if(|_, _| unreachable!("there's nothing to decide on")).for_each(drop);
         assert!(map.is_empty());
     }
 
@@ -976,7 +976,7 @@ mod test_drain_filter {
     fn consuming_nothing() {
         let pairs = (0..3).map(|i| (i, i));
         let mut map: HashMap<_, _> = pairs.collect();
-        assert!(map.drain_filter(|_, _| false).eq_sorted(crate::iter::empty()));
+        assert!(map.extract_if(|_, _| false).eq_sorted(crate::iter::empty()));
         assert_eq!(map.len(), 3);
     }
 
@@ -984,7 +984,7 @@ mod test_drain_filter {
     fn consuming_all() {
         let pairs = (0..3).map(|i| (i, i));
         let mut map: HashMap<_, _> = pairs.clone().collect();
-        assert!(map.drain_filter(|_, _| true).eq_sorted(pairs));
+        assert!(map.extract_if(|_, _| true).eq_sorted(pairs));
         assert!(map.is_empty());
     }
 
@@ -993,7 +993,7 @@ mod test_drain_filter {
         let pairs = (0..3).map(|i| (i, i));
         let mut map: HashMap<_, _> = pairs.collect();
         assert!(
-            map.drain_filter(|_, v| {
+            map.extract_if(|_, v| {
                 *v += 6;
                 false
             })
@@ -1008,7 +1008,7 @@ mod test_drain_filter {
         let pairs = (0..3).map(|i| (i, i));
         let mut map: HashMap<_, _> = pairs.collect();
         assert!(
-            map.drain_filter(|_, v| {
+            map.extract_if(|_, v| {
                 *v += 6;
                 true
             })
@@ -1034,14 +1034,15 @@ mod test_drain_filter {
         let mut map = (0..3).map(|i| (i, D)).collect::<HashMap<_, _>>();
 
         catch_unwind(move || {
-            drop(map.drain_filter(|_, _| {
+            map.extract_if(|_, _| {
                 PREDS.fetch_add(1, Ordering::SeqCst);
                 true
-            }))
+            })
+            .for_each(drop)
         })
         .unwrap_err();
 
-        assert_eq!(PREDS.load(Ordering::SeqCst), 3);
+        assert_eq!(PREDS.load(Ordering::SeqCst), 2);
         assert_eq!(DROPS.load(Ordering::SeqCst), 3);
     }
 
@@ -1060,10 +1061,11 @@ mod test_drain_filter {
         let mut map = (0..3).map(|i| (i, D)).collect::<HashMap<_, _>>();
 
         catch_unwind(AssertUnwindSafe(|| {
-            drop(map.drain_filter(|_, _| match PREDS.fetch_add(1, Ordering::SeqCst) {
+            map.extract_if(|_, _| match PREDS.fetch_add(1, Ordering::SeqCst) {
                 0 => true,
                 _ => panic!(),
-            }))
+            })
+            .for_each(drop)
         }))
         .unwrap_err();
 
@@ -1088,7 +1090,7 @@ mod test_drain_filter {
         let mut map = (0..3).map(|i| (i, D)).collect::<HashMap<_, _>>();
 
         {
-            let mut it = map.drain_filter(|_, _| match PREDS.fetch_add(1, Ordering::SeqCst) {
+            let mut it = map.extract_if(|_, _| match PREDS.fetch_add(1, Ordering::SeqCst) {
                 0 => true,
                 _ => panic!(),
             });
diff --git a/library/std/src/collections/hash/set.rs b/library/std/src/collections/hash/set.rs
index ac906e682d5..ec59634df36 100644
--- a/library/std/src/collections/hash/set.rs
+++ b/library/std/src/collections/hash/set.rs
@@ -262,25 +262,24 @@ impl<T, S> HashSet<T, S> {
     /// If the closure returns false, the value will remain in the list and will not be yielded
     /// by the iterator.
     ///
-    /// If the iterator is only partially consumed or not consumed at all, each of the remaining
-    /// values will still be subjected to the closure and removed and dropped if it returns true.
+    /// 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.
     ///
-    /// It is unspecified how many more values will be subjected to the closure
-    /// if a panic occurs in the closure, or if a panic occurs while dropping a value, or if the
-    /// `DrainFilter` itself is leaked.
+    /// [`retain`]: HashSet::retain
     ///
     /// # Examples
     ///
     /// Splitting a set into even and odd values, reusing the original set:
     ///
     /// ```
-    /// #![feature(hash_drain_filter)]
+    /// #![feature(hash_extract_if)]
     /// use std::collections::HashSet;
     ///
     /// let mut set: HashSet<i32> = (0..8).collect();
-    /// let drained: HashSet<i32> = set.drain_filter(|v| v % 2 == 0).collect();
+    /// let extracted: HashSet<i32> = set.extract_if(|v| v % 2 == 0).collect();
     ///
-    /// let mut evens = drained.into_iter().collect::<Vec<_>>();
+    /// let mut evens = extracted.into_iter().collect::<Vec<_>>();
     /// let mut odds = set.into_iter().collect::<Vec<_>>();
     /// evens.sort();
     /// odds.sort();
@@ -290,12 +289,12 @@ impl<T, S> HashSet<T, S> {
     /// ```
     #[inline]
     #[rustc_lint_query_instability]
-    #[unstable(feature = "hash_drain_filter", issue = "59618")]
-    pub fn drain_filter<F>(&mut self, pred: F) -> DrainFilter<'_, T, F>
+    #[unstable(feature = "hash_extract_if", issue = "59618")]
+    pub fn extract_if<F>(&mut self, pred: F) -> ExtractIf<'_, T, F>
     where
         F: FnMut(&T) -> bool,
     {
-        DrainFilter { base: self.base.drain_filter(pred) }
+        ExtractIf { base: self.base.extract_if(pred) }
     }
 
     /// Retains only the elements specified by the predicate.
@@ -868,7 +867,9 @@ where
     /// Returns whether the value was newly inserted. That is:
     ///
     /// - If the set did not previously contain this value, `true` is returned.
-    /// - If the set already contained this value, `false` is returned.
+    /// - If the set already contained this value, `false` is returned,
+    ///   and the set is not modified: original value is not replaced,
+    ///   and the value passed as argument is dropped.
     ///
     /// # Examples
     ///
@@ -1310,27 +1311,27 @@ pub struct Drain<'a, K: 'a> {
 
 /// A draining, filtering iterator over the items of a `HashSet`.
 ///
-/// This `struct` is created by the [`drain_filter`] method on [`HashSet`].
+/// This `struct` is created by the [`extract_if`] method on [`HashSet`].
 ///
-/// [`drain_filter`]: HashSet::drain_filter
+/// [`extract_if`]: HashSet::extract_if
 ///
 /// # Examples
 ///
 /// ```
-/// #![feature(hash_drain_filter)]
+/// #![feature(hash_extract_if)]
 ///
 /// use std::collections::HashSet;
 ///
 /// let mut a = HashSet::from([1, 2, 3]);
 ///
-/// let mut drain_filtered = a.drain_filter(|v| v % 2 == 0);
+/// let mut extract_ifed = a.extract_if(|v| v % 2 == 0);
 /// ```
-#[unstable(feature = "hash_drain_filter", issue = "59618")]
-pub struct DrainFilter<'a, K, F>
+#[unstable(feature = "hash_extract_if", issue = "59618")]
+pub struct ExtractIf<'a, K, F>
 where
     F: FnMut(&K) -> bool,
 {
-    base: base::DrainFilter<'a, K, F>,
+    base: base::ExtractIf<'a, K, F>,
 }
 
 /// A lazy iterator producing elements in the intersection of `HashSet`s.
@@ -1576,8 +1577,8 @@ impl<K: fmt::Debug> fmt::Debug for Drain<'_, K> {
     }
 }
 
-#[unstable(feature = "hash_drain_filter", issue = "59618")]
-impl<K, F> Iterator for DrainFilter<'_, K, F>
+#[unstable(feature = "hash_extract_if", issue = "59618")]
+impl<K, F> Iterator for ExtractIf<'_, K, F>
 where
     F: FnMut(&K) -> bool,
 {
@@ -1593,16 +1594,16 @@ where
     }
 }
 
-#[unstable(feature = "hash_drain_filter", issue = "59618")]
-impl<K, F> FusedIterator for DrainFilter<'_, K, F> where F: FnMut(&K) -> bool {}
+#[unstable(feature = "hash_extract_if", issue = "59618")]
+impl<K, F> FusedIterator for ExtractIf<'_, K, F> where F: FnMut(&K) -> bool {}
 
-#[unstable(feature = "hash_drain_filter", issue = "59618")]
-impl<'a, K, F> fmt::Debug for DrainFilter<'a, K, F>
+#[unstable(feature = "hash_extract_if", issue = "59618")]
+impl<'a, K, F> fmt::Debug for ExtractIf<'a, K, F>
 where
     F: FnMut(&K) -> bool,
 {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        f.debug_struct("DrainFilter").finish_non_exhaustive()
+        f.debug_struct("ExtractIf").finish_non_exhaustive()
     }
 }
 
diff --git a/library/std/src/collections/hash/set/tests.rs b/library/std/src/collections/hash/set/tests.rs
index 941a0450cc7..e0cd80b44f8 100644
--- a/library/std/src/collections/hash/set/tests.rs
+++ b/library/std/src/collections/hash/set/tests.rs
@@ -3,6 +3,7 @@ use super::HashSet;
 
 use crate::panic::{catch_unwind, AssertUnwindSafe};
 use crate::sync::atomic::{AtomicU32, Ordering};
+use crate::sync::Arc;
 
 #[test]
 fn test_zero_capacities() {
@@ -418,18 +419,18 @@ fn test_retain() {
 }
 
 #[test]
-fn test_drain_filter() {
+fn test_extract_if() {
     let mut x: HashSet<_> = [1].iter().copied().collect();
     let mut y: HashSet<_> = [1].iter().copied().collect();
 
-    x.drain_filter(|_| true);
-    y.drain_filter(|_| false);
+    x.extract_if(|_| true).for_each(drop);
+    y.extract_if(|_| false).for_each(drop);
     assert_eq!(x.len(), 0);
     assert_eq!(y.len(), 1);
 }
 
 #[test]
-fn test_drain_filter_drop_panic_leak() {
+fn test_extract_if_drop_panic_leak() {
     static PREDS: AtomicU32 = AtomicU32::new(0);
     static DROPS: AtomicU32 = AtomicU32::new(0);
 
@@ -446,19 +447,20 @@ fn test_drain_filter_drop_panic_leak() {
     let mut set = (0..3).map(|i| D(i)).collect::<HashSet<_>>();
 
     catch_unwind(move || {
-        drop(set.drain_filter(|_| {
+        set.extract_if(|_| {
             PREDS.fetch_add(1, Ordering::SeqCst);
             true
-        }))
+        })
+        .for_each(drop)
     })
     .ok();
 
-    assert_eq!(PREDS.load(Ordering::SeqCst), 3);
+    assert_eq!(PREDS.load(Ordering::SeqCst), 2);
     assert_eq!(DROPS.load(Ordering::SeqCst), 3);
 }
 
 #[test]
-fn test_drain_filter_pred_panic_leak() {
+fn test_extract_if_pred_panic_leak() {
     static PREDS: AtomicU32 = AtomicU32::new(0);
     static DROPS: AtomicU32 = AtomicU32::new(0);
 
@@ -473,10 +475,11 @@ fn test_drain_filter_pred_panic_leak() {
     let mut set: HashSet<_> = (0..3).map(|_| D).collect();
 
     catch_unwind(AssertUnwindSafe(|| {
-        drop(set.drain_filter(|_| match PREDS.fetch_add(1, Ordering::SeqCst) {
+        set.extract_if(|_| match PREDS.fetch_add(1, Ordering::SeqCst) {
             0 => true,
             _ => panic!(),
-        }))
+        })
+        .for_each(drop)
     }))
     .ok();
 
@@ -502,3 +505,22 @@ fn const_with_hasher() {
     const X: HashSet<(), ()> = HashSet::with_hasher(());
     assert_eq!(X.len(), 0);
 }
+
+#[test]
+fn test_insert_does_not_overwrite_the_value() {
+    let first_value = Arc::new(17);
+    let second_value = Arc::new(17);
+
+    let mut set = HashSet::new();
+    let inserted = set.insert(first_value.clone());
+    assert!(inserted);
+
+    let inserted = set.insert(second_value);
+    assert!(!inserted);
+
+    assert!(
+        Arc::ptr_eq(set.iter().next().unwrap(), &first_value),
+        "Insert must not overwrite the value, so the contained value pointer \
+            must be the same as first value pointer we inserted"
+    );
+}
diff --git a/library/std/src/f32.rs b/library/std/src/f32.rs
index 408244b2ce9..bed90418be1 100644
--- a/library/std/src/f32.rs
+++ b/library/std/src/f32.rs
@@ -528,7 +528,7 @@ impl f32 {
 
     /// The positive difference of two numbers.
     ///
-    /// * If `self <= other`: `0:0`
+    /// * If `self <= other`: `0.0`
     /// * Else: `self - other`
     ///
     /// # Examples
diff --git a/library/std/src/f64.rs b/library/std/src/f64.rs
index 6782b861f11..e72de05ca41 100644
--- a/library/std/src/f64.rs
+++ b/library/std/src/f64.rs
@@ -530,7 +530,7 @@ impl f64 {
 
     /// The positive difference of two numbers.
     ///
-    /// * If `self <= other`: `0:0`
+    /// * If `self <= other`: `0.0`
     /// * Else: `self - other`
     ///
     /// # Examples
diff --git a/library/std/src/ffi/os_str.rs b/library/std/src/ffi/os_str.rs
index bb577acf769..fbdf7f5ecac 100644
--- a/library/std/src/ffi/os_str.rs
+++ b/library/std/src/ffi/os_str.rs
@@ -745,7 +745,7 @@ impl OsStr {
                   without modifying the original"]
     #[inline]
     pub fn to_str(&self) -> Option<&str> {
-        self.inner.to_str()
+        self.inner.to_str().ok()
     }
 
     /// Converts an `OsStr` to a <code>[Cow]<[str]></code>.
@@ -1165,6 +1165,24 @@ impl<'a> From<Cow<'a, OsStr>> for OsString {
     }
 }
 
+#[stable(feature = "str_tryfrom_osstr_impl", since = "CURRENT_RUSTC_VERSION")]
+impl<'a> TryFrom<&'a OsStr> for &'a str {
+    type Error = crate::str::Utf8Error;
+
+    /// Tries to convert an `&OsStr` to a `&str`.
+    ///
+    /// ```
+    /// use std::ffi::OsStr;
+    ///
+    /// let os_str = OsStr::new("foo");
+    /// let as_str = <&str>::try_from(os_str).unwrap();
+    /// assert_eq!(as_str, "foo");
+    /// ```
+    fn try_from(value: &'a OsStr) -> Result<Self, Self::Error> {
+        value.inner.to_str()
+    }
+}
+
 #[stable(feature = "box_default_extra", since = "1.17.0")]
 impl Default for Box<OsStr> {
     #[inline]
diff --git a/library/std/src/sys/common/thread_local/fast_local.rs b/library/std/src/sys/common/thread_local/fast_local.rs
index 447044a798b..bc5da1a1896 100644
--- a/library/std/src/sys/common/thread_local/fast_local.rs
+++ b/library/std/src/sys/common/thread_local/fast_local.rs
@@ -33,20 +33,21 @@ pub macro thread_local_inner {
             // 1 == dtor registered, dtor not run
             // 2 == dtor registered and is running or has run
             #[thread_local]
-            static mut STATE: $crate::primitive::u8 = 0;
+            static STATE: $crate::cell::Cell<$crate::primitive::u8> = $crate::cell::Cell::new(0);
 
+            // Safety: Performs `drop_in_place(ptr as *mut $t)`, and requires
+            // all that comes with it.
             unsafe extern "C" fn destroy(ptr: *mut $crate::primitive::u8) {
-                let ptr = ptr as *mut $t;
-
-                unsafe {
-                    $crate::debug_assert_eq!(STATE, 1);
-                    STATE = 2;
-                    $crate::ptr::drop_in_place(ptr);
-                }
+                $crate::thread::local_impl::abort_on_dtor_unwind(|| {
+                    let old_state = STATE.replace(2);
+                    $crate::debug_assert_eq!(old_state, 1);
+                    // Safety: safety requirement is passed on to caller.
+                    unsafe { $crate::ptr::drop_in_place(ptr.cast::<$t>()); }
+                });
             }
 
             unsafe {
-                match STATE {
+                match STATE.get() {
                     // 0 == we haven't registered a destructor, so do
                     //   so now.
                     0 => {
@@ -54,7 +55,7 @@ pub macro thread_local_inner {
                             $crate::ptr::addr_of_mut!(VAL) as *mut $crate::primitive::u8,
                             destroy,
                         );
-                        STATE = 1;
+                        STATE.set(1);
                         $crate::option::Option::Some(&VAL)
                     }
                     // 1 == the destructor is registered and the value
@@ -148,7 +149,6 @@ impl<T> fmt::Debug for Key<T> {
         f.debug_struct("Key").finish_non_exhaustive()
     }
 }
-
 impl<T> Key<T> {
     pub const fn new() -> Key<T> {
         Key { inner: LazyKeyInner::new(), dtor_state: Cell::new(DtorState::Unregistered) }
diff --git a/library/std/src/sys/common/thread_local/mod.rs b/library/std/src/sys/common/thread_local/mod.rs
index 77f64588310..975509bd412 100644
--- a/library/std/src/sys/common/thread_local/mod.rs
+++ b/library/std/src/sys/common/thread_local/mod.rs
@@ -101,3 +101,24 @@ mod lazy {
         }
     }
 }
+
+/// Run a callback in a scenario which must not unwind (such as a `extern "C"
+/// fn` declared in a user crate). If the callback unwinds anyway, then
+/// `rtabort` with a message about thread local panicking on drop.
+#[inline]
+pub fn abort_on_dtor_unwind(f: impl FnOnce()) {
+    // Using a guard like this is lower cost.
+    let guard = DtorUnwindGuard;
+    f();
+    core::mem::forget(guard);
+
+    struct DtorUnwindGuard;
+    impl Drop for DtorUnwindGuard {
+        #[inline]
+        fn drop(&mut self) {
+            // This is not terribly descriptive, but it doesn't need to be as we'll
+            // already have printed a panic message at this point.
+            rtabort!("thread local panicked on drop");
+        }
+    }
+}
diff --git a/library/std/src/sys/unix/os_str.rs b/library/std/src/sys/unix/os_str.rs
index 142fcb9ed0b..f7333fd5a1f 100644
--- a/library/std/src/sys/unix/os_str.rs
+++ b/library/std/src/sys/unix/os_str.rs
@@ -207,8 +207,8 @@ impl Slice {
         unsafe { Slice::from_os_str_bytes_unchecked(s.as_bytes()) }
     }
 
-    pub fn to_str(&self) -> Option<&str> {
-        str::from_utf8(&self.inner).ok()
+    pub fn to_str(&self) -> Result<&str, crate::str::Utf8Error> {
+        str::from_utf8(&self.inner)
     }
 
     pub fn to_string_lossy(&self) -> Cow<'_, str> {
diff --git a/library/std/src/sys/windows/c.rs b/library/std/src/sys/windows/c.rs
index 07b0610d463..5fc6136ba1f 100644
--- a/library/std/src/sys/windows/c.rs
+++ b/library/std/src/sys/windows/c.rs
@@ -19,6 +19,7 @@ pub use windows_sys::*;
 pub type DWORD = c_ulong;
 pub type NonZeroDWORD = NonZero_c_ulong;
 pub type LARGE_INTEGER = c_longlong;
+#[cfg_attr(target_vendor = "uwp", allow(unused))]
 pub type LONG = c_long;
 pub type UINT = c_uint;
 pub type WCHAR = u16;
@@ -267,6 +268,8 @@ pub unsafe fn getaddrinfo(
     windows_sys::getaddrinfo(node.cast::<u8>(), service.cast::<u8>(), hints, res)
 }
 
+cfg_if::cfg_if! {
+if #[cfg(not(target_vendor = "uwp"))] {
 pub unsafe fn NtReadFile(
     filehandle: BorrowedHandle<'_>,
     event: HANDLE,
@@ -313,6 +316,8 @@ pub unsafe fn NtWriteFile(
         key.map(|k| k as *const u32).unwrap_or(ptr::null()),
     )
 }
+}
+}
 
 // Functions that aren't available on every version of Windows that we support,
 // but we still use them and just provide some form of a fallback implementation.
@@ -376,4 +381,54 @@ compat_fn_with_fallback! {
     ) -> NTSTATUS {
         panic!("keyed events not available")
     }
+
+    // These functions are available on UWP when lazily loaded. They will fail WACK if loaded statically.
+    #[cfg(target_vendor = "uwp")]
+    pub fn NtCreateFile(
+        filehandle: *mut HANDLE,
+        desiredaccess: FILE_ACCESS_RIGHTS,
+        objectattributes: *const OBJECT_ATTRIBUTES,
+        iostatusblock: *mut IO_STATUS_BLOCK,
+        allocationsize: *const i64,
+        fileattributes: FILE_FLAGS_AND_ATTRIBUTES,
+        shareaccess: FILE_SHARE_MODE,
+        createdisposition: NTCREATEFILE_CREATE_DISPOSITION,
+        createoptions: NTCREATEFILE_CREATE_OPTIONS,
+        eabuffer: *const ::core::ffi::c_void,
+        ealength: u32
+    ) -> NTSTATUS {
+        STATUS_NOT_IMPLEMENTED
+    }
+    #[cfg(target_vendor = "uwp")]
+    pub fn NtReadFile(
+        filehandle: BorrowedHandle<'_>,
+        event: HANDLE,
+        apcroutine: PIO_APC_ROUTINE,
+        apccontext: *mut c_void,
+        iostatusblock: &mut IO_STATUS_BLOCK,
+        buffer: *mut crate::mem::MaybeUninit<u8>,
+        length: ULONG,
+        byteoffset: Option<&LARGE_INTEGER>,
+        key: Option<&ULONG>
+    ) -> NTSTATUS {
+        STATUS_NOT_IMPLEMENTED
+    }
+    #[cfg(target_vendor = "uwp")]
+    pub fn NtWriteFile(
+        filehandle: BorrowedHandle<'_>,
+        event: HANDLE,
+        apcroutine: PIO_APC_ROUTINE,
+        apccontext: *mut c_void,
+        iostatusblock: &mut IO_STATUS_BLOCK,
+        buffer: *const u8,
+        length: ULONG,
+        byteoffset: Option<&LARGE_INTEGER>,
+        key: Option<&ULONG>
+    ) -> NTSTATUS {
+        STATUS_NOT_IMPLEMENTED
+    }
+    #[cfg(target_vendor = "uwp")]
+    pub fn RtlNtStatusToDosError(Status: NTSTATUS) -> u32 {
+        Status as u32
+    }
 }
diff --git a/library/std/src/sys/windows/c/windows_sys.lst b/library/std/src/sys/windows/c/windows_sys.lst
index 3e454199f13..2cf1ade99ce 100644
--- a/library/std/src/sys/windows/c/windows_sys.lst
+++ b/library/std/src/sys/windows/c/windows_sys.lst
@@ -1930,6 +1930,7 @@ Windows.Win32.Foundation.SetLastError
 Windows.Win32.Foundation.STATUS_DELETE_PENDING
 Windows.Win32.Foundation.STATUS_END_OF_FILE
 Windows.Win32.Foundation.STATUS_INVALID_PARAMETER
+Windows.Win32.Foundation.STATUS_NOT_IMPLEMENTED
 Windows.Win32.Foundation.STATUS_PENDING
 Windows.Win32.Foundation.STATUS_SUCCESS
 Windows.Win32.Foundation.TRUE
diff --git a/library/std/src/sys/windows/c/windows_sys.rs b/library/std/src/sys/windows/c/windows_sys.rs
index 36a30f6ba56..a4294f336fe 100644
--- a/library/std/src/sys/windows/c/windows_sys.rs
+++ b/library/std/src/sys/windows/c/windows_sys.rs
@@ -3888,6 +3888,7 @@ pub type STARTUPINFOW_FLAGS = u32;
 pub const STATUS_DELETE_PENDING: NTSTATUS = -1073741738i32;
 pub const STATUS_END_OF_FILE: NTSTATUS = -1073741807i32;
 pub const STATUS_INVALID_PARAMETER: NTSTATUS = -1073741811i32;
+pub const STATUS_NOT_IMPLEMENTED: NTSTATUS = -1073741822i32;
 pub const STATUS_PENDING: NTSTATUS = 259i32;
 pub const STATUS_SUCCESS: NTSTATUS = 0i32;
 pub const STD_ERROR_HANDLE: STD_HANDLE = 4294967284u32;
@@ -4274,3 +4275,23 @@ impl ::core::clone::Clone for XSAVE_FORMAT {
         *self
     }
 }
+// Begin of ARM32 shim
+// The raw content of this file should be processed by `generate-windows-sys`
+// to be merged with the generated binding. It is not supposed to be used as
+// a normal Rust module.
+cfg_if::cfg_if! {
+if #[cfg(target_arch = "arm")] {
+#[repr(C)]
+pub struct WSADATA {
+    pub wVersion: u16,
+    pub wHighVersion: u16,
+    pub szDescription: [u8; 257],
+    pub szSystemStatus: [u8; 129],
+    pub iMaxSockets: u16,
+    pub iMaxUdpDg: u16,
+    pub lpVendorInfo: PSTR,
+}
+pub enum CONTEXT {}
+}
+}
+// End of ARM32 shim
diff --git a/library/std/src/sys/windows/os_str.rs b/library/std/src/sys/windows/os_str.rs
index 611f0d040f0..16c4f55c687 100644
--- a/library/std/src/sys/windows/os_str.rs
+++ b/library/std/src/sys/windows/os_str.rs
@@ -166,7 +166,7 @@ impl Slice {
         unsafe { mem::transmute(Wtf8::from_str(s)) }
     }
 
-    pub fn to_str(&self) -> Option<&str> {
+    pub fn to_str(&self) -> Result<&str, crate::str::Utf8Error> {
         self.inner.as_str()
     }
 
diff --git a/library/std/src/sys/windows/rand.rs b/library/std/src/sys/windows/rand.rs
index bca4e38d9f6..5d8fd13785a 100644
--- a/library/std/src/sys/windows/rand.rs
+++ b/library/std/src/sys/windows/rand.rs
@@ -1,5 +1,3 @@
-use crate::ffi::c_void;
-use crate::io;
 use crate::mem;
 use crate::ptr;
 use crate::sys::c;
@@ -25,6 +23,9 @@ pub fn hashmap_random_keys() -> (u64, u64) {
 #[cfg(not(target_vendor = "uwp"))]
 #[inline(never)]
 fn fallback_rng() -> (u64, u64) {
+    use crate::ffi::c_void;
+    use crate::io;
+
     let mut v = (0, 0);
     let ret = unsafe {
         c::RtlGenRandom(&mut v as *mut _ as *mut c_void, mem::size_of_val(&v) as c::ULONG)
diff --git a/library/std/src/sys_common/wtf8.rs b/library/std/src/sys_common/wtf8.rs
index 31bb0ad25a6..c9d3e13cf0c 100644
--- a/library/std/src/sys_common/wtf8.rs
+++ b/library/std/src/sys_common/wtf8.rs
@@ -626,13 +626,8 @@ impl Wtf8 {
     ///
     /// This does not copy the data.
     #[inline]
-    pub fn as_str(&self) -> Option<&str> {
-        // Well-formed WTF-8 is also well-formed UTF-8
-        // if and only if it contains no surrogate.
-        match self.next_surrogate(0) {
-            None => Some(unsafe { str::from_utf8_unchecked(&self.bytes) }),
-            Some(_) => None,
-        }
+    pub fn as_str(&self) -> Result<&str, str::Utf8Error> {
+        str::from_utf8(&self.bytes)
     }
 
     /// Creates an owned `Wtf8Buf` from a borrowed `Wtf8`.
diff --git a/library/std/src/sys_common/wtf8/tests.rs b/library/std/src/sys_common/wtf8/tests.rs
index 1a302d64694..a07bbe6d7e4 100644
--- a/library/std/src/sys_common/wtf8/tests.rs
+++ b/library/std/src/sys_common/wtf8/tests.rs
@@ -521,11 +521,11 @@ fn wtf8_code_points() {
 
 #[test]
 fn wtf8_as_str() {
-    assert_eq!(Wtf8::from_str("").as_str(), Some(""));
-    assert_eq!(Wtf8::from_str("aé 💩").as_str(), Some("aé 💩"));
+    assert_eq!(Wtf8::from_str("").as_str(), Ok(""));
+    assert_eq!(Wtf8::from_str("aé 💩").as_str(), Ok("aé 💩"));
     let mut string = Wtf8Buf::new();
     string.push(CodePoint::from_u32(0xD800).unwrap());
-    assert_eq!(string.as_str(), None);
+    assert!(string.as_str().is_err());
 }
 
 #[test]
diff --git a/library/std/src/thread/mod.rs b/library/std/src/thread/mod.rs
index f712c872708..1230bb5deed 100644
--- a/library/std/src/thread/mod.rs
+++ b/library/std/src/thread/mod.rs
@@ -195,7 +195,7 @@ mod local;
 
 cfg_if::cfg_if! {
     if #[cfg(test)] {
-        // Avoid duplicating the global state assoicated with thread-locals between this crate and
+        // Avoid duplicating the global state associated with thread-locals between this crate and
         // realstd. Miri relies on this.
         pub use realstd::thread::{local_impl, AccessError, LocalKey};
     } else {
@@ -206,7 +206,7 @@ cfg_if::cfg_if! {
         #[doc(hidden)]
         #[unstable(feature = "thread_local_internals", issue = "none")]
         pub mod local_impl {
-            pub use crate::sys::common::thread_local::{thread_local_inner, Key};
+            pub use crate::sys::common::thread_local::{thread_local_inner, Key, abort_on_dtor_unwind};
         }
     }
 }