Auto merge of rust-lang#134812 - jhpratt:rollup-a9klvez, r=jhpratt

Rollup of 8 pull requests

Successful merges:

 - rust-lang#131522 ([macro_metavar_expr_concat] Fix rust-lang#128346)
 - rust-lang#134379 (Add `into_array` conversion destructors for `Box`, `Rc`, and `Arc`.)
 - rust-lang#134644 (Document collection `From` and `FromIterator` impls that drop duplicate keys.)
 - rust-lang#134649 (Fix forgetting to save statx availability on success)
 - rust-lang#134728 (Use scoped threads in `std::sync::Barrier` examples)
 - rust-lang#134782 (Update Code Example for `Iterator::rposition`)
 - rust-lang#134789 (unwinding: bump version to fix naked_asm on Xous)
 - rust-lang#134791 (docs: inline `std::ffi::c_str` types to `std::ffi`)

r? `@ghost`
`@rustbot` modify labels: rollup

Author: bors

compiler/rustc_expand/src/mbe/transcribe.rs

@@ -697,8 +697,10 @@ fn transcribe_metavar_expr<'a>(
                     MetaVarExprConcatElem::Var(ident) => {
                         match matched_from_ident(dcx, *ident, interp)? {
                             NamedMatch::MatchedSeq(named_matches) => {
-                                let curr_idx = repeats.last().unwrap().0;
-                                match &named_matches[curr_idx] {
+                                let Some((curr_idx, _)) = repeats.last() else {
+                                    return Err(dcx.struct_span_err(sp.entire(), "invalid syntax"));
+                                };
+                                match &named_matches[*curr_idx] {
                                     // FIXME(c410-f3r) Nested repetitions are unimplemented
                                     MatchedSeq(_) => unimplemented!(),
                                     MatchedSingle(pnr) => {

library/Cargo.lock

@@ -403,9 +403,9 @@ dependencies = [
 
 [[package]]
 name = "unwinding"
-version = "0.2.4"
+version = "0.2.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "e2c6cb20f236dae10c69b0b45d82ef50af8b7e45c10e429e7901d26b49b4dbf3"
+checksum = "51f06a05848f650946acef3bf525fe96612226b61f74ae23ffa4e98bfbb8ab3c"
 dependencies = [
  "compiler_builtins",
  "gimli 0.31.1",

library/alloc/src/boxed.rs

@@ -761,6 +761,26 @@ impl<T> Box<[T]> {
         };
         unsafe { Ok(RawVec::from_raw_parts_in(ptr.as_ptr(), len, Global).into_box(len)) }
     }
+
+    /// Converts the boxed slice into a boxed array.
+    ///
+    /// This operation does not reallocate; the underlying array of the slice is simply reinterpreted as an array type.
+    ///
+    /// If `N` is not exactly equal to the length of `self`, then this method returns `None`.
+    #[unstable(feature = "slice_as_array", issue = "133508")]
+    #[inline]
+    #[must_use]
+    pub fn into_array<const N: usize>(self) -> Option<Box<[T; N]>> {
+        if self.len() == N {
+            let ptr = Self::into_raw(self) as *mut [T; N];
+
+            // SAFETY: The underlying array of a slice has the exact same layout as an actual array `[T; N]` if `N` is equal to the slice's length.
+            let me = unsafe { Box::from_raw(ptr) };
+            Some(me)
+        } else {
+            None
+        }
+    }
 }
 
 impl<T, A: Allocator> Box<[T], A> {

library/alloc/src/collections/btree/map.rs

@@ -2289,6 +2289,10 @@ impl<K, V> FusedIterator for RangeMut<'_, K, V> {}
 
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<K: Ord, V> FromIterator<(K, V)> for BTreeMap<K, V> {
+    /// Constructs a `BTreeMap<K, V>` from an iterator of key-value pairs.
+    ///
+    /// If the iterator produces any pairs with equal keys,
+    /// all but one of the corresponding values will be dropped.
     fn from_iter<T: IntoIterator<Item = (K, V)>>(iter: T) -> BTreeMap<K, V> {
         let mut inputs: Vec<_> = iter.into_iter().collect();
 
@@ -2403,7 +2407,10 @@ where
 
 #[stable(feature = "std_collections_from_array", since = "1.56.0")]
 impl<K: Ord, V, const N: usize> From<[(K, V); N]> for BTreeMap<K, V> {
-    /// Converts a `[(K, V); N]` into a `BTreeMap<(K, V)>`.
+    /// Converts a `[(K, V); N]` into a `BTreeMap<K, V>`.
+    ///
+    /// If any entries in the array have equal keys,
+    /// all but one of the corresponding values will be dropped.
     ///
     /// ```
     /// use std::collections::BTreeMap;

library/alloc/src/collections/btree/set.rs

@@ -1491,6 +1491,11 @@ impl<T: Ord, A: Allocator + Clone> BTreeSet<T, A> {
 impl<T: Ord, const N: usize> From<[T; N]> for BTreeSet<T> {
     /// Converts a `[T; N]` into a `BTreeSet<T>`.
     ///
+    /// If the array contains any equal values,
+    /// all but one will be dropped.
+    ///
+    /// # Examples
+    ///
     /// ```
     /// use std::collections::BTreeSet;
     ///

library/alloc/src/rc.rs

@@ -1084,6 +1084,26 @@ impl<T> Rc<[T]> {
             ))
         }
     }
+
+    /// Converts the reference-counted slice into a reference-counted array.
+    ///
+    /// This operation does not reallocate; the underlying array of the slice is simply reinterpreted as an array type.
+    ///
+    /// If `N` is not exactly equal to the length of `self`, then this method returns `None`.
+    #[unstable(feature = "slice_as_array", issue = "133508")]
+    #[inline]
+    #[must_use]
+    pub fn into_array<const N: usize>(self) -> Option<Rc<[T; N]>> {
+        if self.len() == N {
+            let ptr = Self::into_raw(self) as *const [T; N];
+
+            // SAFETY: The underlying array of a slice has the exact same layout as an actual array `[T; N]` if `N` is equal to the slice's length.
+            let me = unsafe { Rc::from_raw(ptr) };
+            Some(me)
+        } else {
+            None
+        }
+    }
 }
 
 impl<T, A: Allocator> Rc<[T], A> {

library/alloc/src/sync.rs

@@ -1203,6 +1203,26 @@ impl<T> Arc<[T]> {
             ))
         }
     }
+
+    /// Converts the reference-counted slice into a reference-counted array.
+    ///
+    /// This operation does not reallocate; the underlying array of the slice is simply reinterpreted as an array type.
+    ///
+    /// If `N` is not exactly equal to the length of `self`, then this method returns `None`.
+    #[unstable(feature = "slice_as_array", issue = "133508")]
+    #[inline]
+    #[must_use]
+    pub fn into_array<const N: usize>(self) -> Option<Arc<[T; N]>> {
+        if self.len() == N {
+            let ptr = Self::into_raw(self) as *const [T; N];
+
+            // SAFETY: The underlying array of a slice has the exact same layout as an actual array `[T; N]` if `N` is equal to the slice's length.
+            let me = unsafe { Arc::from_raw(ptr) };
+            Some(me)
+        } else {
+            None
+        }
+    }
 }
 
 impl<T, A: Allocator> Arc<[T], A> {

library/core/src/ffi/mod.rs

@@ -12,10 +12,10 @@
 #[doc(inline)]
 #[stable(feature = "core_c_str", since = "1.64.0")]
 pub use self::c_str::CStr;
-#[doc(no_inline)]
+#[doc(inline)]
 #[stable(feature = "cstr_from_bytes_until_nul", since = "1.69.0")]
 pub use self::c_str::FromBytesUntilNulError;
-#[doc(no_inline)]
+#[doc(inline)]
 #[stable(feature = "core_c_str", since = "1.64.0")]
 pub use self::c_str::FromBytesWithNulError;
 use crate::fmt;

library/core/src/iter/traits/iterator.rs

@@ -3051,6 +3051,7 @@ pub trait Iterator {
     ///
     /// // we can still use `iter`, as there are more elements.
     /// assert_eq!(iter.next(), Some(&-1));
+    /// assert_eq!(iter.next_back(), Some(&3));
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]

library/std/src/collections/hash/map.rs

@@ -1446,6 +1446,11 @@ impl<K, V, const N: usize> From<[(K, V); N]> for HashMap<K, V, RandomState>
 where
     K: Eq + Hash,
 {
+    /// Converts a `[(K, V); N]` into a `HashMap<K, V>`.
+    ///
+    /// If any entries in the array have equal keys,
+    /// all but one of the corresponding values will be dropped.
+    ///
     /// # Examples
     ///
     /// ```
@@ -3219,6 +3224,10 @@ where
     K: Eq + Hash,
     S: BuildHasher + Default,
 {
+    /// Constructs a `HashMap<K, V>` from an iterator of key-value pairs.
+    ///
+    /// If the iterator produces any pairs with equal keys,
+    /// all but one of the corresponding values will be dropped.
     fn from_iter<T: IntoIterator<Item = (K, V)>>(iter: T) -> HashMap<K, V, S> {
         let mut map = HashMap::with_hasher(Default::default());
         map.extend(iter);