Merging upstream version 1.71.1+dfsg1.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

8 files changed, 179 insertions, 45 deletions

diff --git a/library/core/src/iter/adapters/chain.rs b/library/core/src/iter/adapters/chain.rs
index 75727c3a2..26aa959e6 100644
--- a/library/core/src/iter/adapters/chain.rs
+++ b/library/core/src/iter/adapters/chain.rs
@@ -15,7 +15,7 @@ use crate::ops::Try;
 ///
 /// let a1 = [1, 2, 3];
 /// let a2 = [4, 5, 6];
-/// let iter: Chain<Iter<_>, Iter<_>> = a1.iter().chain(a2.iter());
+/// let iter: Chain<Iter<'_, _>, Iter<'_, _>> = a1.iter().chain(a2.iter());
 /// ```
 #[derive(Clone, Debug)]
 #[must_use = "iterators are lazy and do nothing unless consumed"]
diff --git a/library/core/src/iter/adapters/filter.rs b/library/core/src/iter/adapters/filter.rs
index a0afaa326..723657b9e 100644
--- a/library/core/src/iter/adapters/filter.rs
+++ b/library/core/src/iter/adapters/filter.rs
@@ -1,6 +1,9 @@
 use crate::fmt;
 use crate::iter::{adapters::SourceIter, FusedIterator, InPlaceIterable};
 use crate::ops::Try;
+use core::array;
+use core::mem::{ManuallyDrop, MaybeUninit};
+use core::ops::ControlFlow;
 
 /// An iterator that filters the elements of `iter` with `predicate`.
 ///
@@ -57,6 +60,58 @@ where
     }
 
     #[inline]
+    fn next_chunk<const N: usize>(
+        &mut self,
+    ) -> Result<[Self::Item; N], array::IntoIter<Self::Item, N>> {
+        let mut array: [MaybeUninit<Self::Item>; N] = MaybeUninit::uninit_array();
+
+        struct Guard<'a, T> {
+            array: &'a mut [MaybeUninit<T>],
+            initialized: usize,
+        }
+
+        impl<T> Drop for Guard<'_, T> {
+            #[inline]
+            fn drop(&mut self) {
+                if const { crate::mem::needs_drop::<T>() } {
+                    // SAFETY: self.initialized is always <= N, which also is the length of the array.
+                    unsafe {
+                        core::ptr::drop_in_place(MaybeUninit::slice_assume_init_mut(
+                            self.array.get_unchecked_mut(..self.initialized),
+                        ));
+                    }
+                }
+            }
+        }
+
+        let mut guard = Guard { array: &mut array, initialized: 0 };
+
+        let result = self.iter.try_for_each(|element| {
+            let idx = guard.initialized;
+            guard.initialized = idx + (self.predicate)(&element) as usize;
+
+            // SAFETY: Loop conditions ensure the index is in bounds.
+            unsafe { guard.array.get_unchecked_mut(idx) }.write(element);
+
+            if guard.initialized < N { ControlFlow::Continue(()) } else { ControlFlow::Break(()) }
+        });
+
+        let guard = ManuallyDrop::new(guard);
+
+        match result {
+            ControlFlow::Break(()) => {
+                // SAFETY: The loop above is only explicitly broken when the array has been fully initialized
+                Ok(unsafe { MaybeUninit::array_assume_init(array) })
+            }
+            ControlFlow::Continue(()) => {
+                let initialized = guard.initialized;
+                // SAFETY: The range is in bounds since the loop breaks when reaching N elements.
+                Err(unsafe { array::IntoIter::new_unchecked(array, 0..initialized) })
+            }
+        }
+    }
+
+    #[inline]
     fn size_hint(&self) -> (usize, Option<usize>) {
         let (_, upper) = self.iter.size_hint();
         (0, upper) // can't know a lower bound, due to the predicate
diff --git a/library/core/src/iter/adapters/filter_map.rs b/library/core/src/iter/adapters/filter_map.rs
index 6bdf53f7f..693479977 100644
--- a/library/core/src/iter/adapters/filter_map.rs
+++ b/library/core/src/iter/adapters/filter_map.rs
@@ -1,6 +1,7 @@
-use crate::fmt;
 use crate::iter::{adapters::SourceIter, FusedIterator, InPlaceIterable};
+use crate::mem::{ManuallyDrop, MaybeUninit};
 use crate::ops::{ControlFlow, Try};
+use crate::{array, fmt};
 
 /// An iterator that uses `f` to both filter and map elements from `iter`.
 ///
@@ -62,6 +63,65 @@ where
     }
 
     #[inline]
+    fn next_chunk<const N: usize>(
+        &mut self,
+    ) -> Result<[Self::Item; N], array::IntoIter<Self::Item, N>> {
+        let mut array: [MaybeUninit<Self::Item>; N] = MaybeUninit::uninit_array();
+
+        struct Guard<'a, T> {
+            array: &'a mut [MaybeUninit<T>],
+            initialized: usize,
+        }
+
+        impl<T> Drop for Guard<'_, T> {
+            #[inline]
+            fn drop(&mut self) {
+                if const { crate::mem::needs_drop::<T>() } {
+                    // SAFETY: self.initialized is always <= N, which also is the length of the array.
+                    unsafe {
+                        core::ptr::drop_in_place(MaybeUninit::slice_assume_init_mut(
+                            self.array.get_unchecked_mut(..self.initialized),
+                        ));
+                    }
+                }
+            }
+        }
+
+        let mut guard = Guard { array: &mut array, initialized: 0 };
+
+        let result = self.iter.try_for_each(|element| {
+            let idx = guard.initialized;
+            let val = (self.f)(element);
+            guard.initialized = idx + val.is_some() as usize;
+
+            // SAFETY: Loop conditions ensure the index is in bounds.
+
+            unsafe {
+                let opt_payload_at = core::intrinsics::option_payload_ptr(&val);
+                let dst = guard.array.as_mut_ptr().add(idx);
+                crate::ptr::copy_nonoverlapping(opt_payload_at.cast(), dst, 1);
+                crate::mem::forget(val);
+            };
+
+            if guard.initialized < N { ControlFlow::Continue(()) } else { ControlFlow::Break(()) }
+        });
+
+        let guard = ManuallyDrop::new(guard);
+
+        match result {
+            ControlFlow::Break(()) => {
+                // SAFETY: The loop above is only explicitly broken when the array has been fully initialized
+                Ok(unsafe { MaybeUninit::array_assume_init(array) })
+            }
+            ControlFlow::Continue(()) => {
+                let initialized = guard.initialized;
+                // SAFETY: The range is in bounds since the loop breaks when reaching N elements.
+                Err(unsafe { array::IntoIter::new_unchecked(array, 0..initialized) })
+            }
+        }
+    }
+
+    #[inline]
     fn size_hint(&self) -> (usize, Option<usize>) {
         let (_, upper) = self.iter.size_hint();
         (0, upper) // can't know a lower bound, due to the predicate
diff --git a/library/core/src/iter/adapters/flatten.rs b/library/core/src/iter/adapters/flatten.rs
index 2fd8a5c1d..2568aaf34 100644
--- a/library/core/src/iter/adapters/flatten.rs
+++ b/library/core/src/iter/adapters/flatten.rs
@@ -136,26 +136,12 @@ where
 }
 
 #[unstable(feature = "trusted_len", issue = "37572")]
-unsafe impl<T, I, F, const N: usize> TrustedLen for FlatMap<I, [T; N], F>
+unsafe impl<I, U, F> TrustedLen for FlatMap<I, U, F>
 where
-    I: TrustedLen,
-    F: FnMut(I::Item) -> [T; N],
-{
-}
-
-#[unstable(feature = "trusted_len", issue = "37572")]
-unsafe impl<'a, T, I, F, const N: usize> TrustedLen for FlatMap<I, &'a [T; N], F>
-where
-    I: TrustedLen,
-    F: FnMut(I::Item) -> &'a [T; N],
-{
-}
-
-#[unstable(feature = "trusted_len", issue = "37572")]
-unsafe impl<'a, T, I, F, const N: usize> TrustedLen for FlatMap<I, &'a mut [T; N], F>
-where
-    I: TrustedLen,
-    F: FnMut(I::Item) -> &'a mut [T; N],
+    I: Iterator,
+    U: IntoIterator,
+    F: FnMut(I::Item) -> U,
+    FlattenCompat<Map<I, F>, <U as IntoIterator>::IntoIter>: TrustedLen,
 {
 }
 
@@ -298,8 +284,8 @@ where
 #[unstable(feature = "trusted_len", issue = "37572")]
 unsafe impl<I> TrustedLen for Flatten<I>
 where
-    I: TrustedLen,
-    <I as Iterator>::Item: TrustedConstSize,
+    I: Iterator<Item: IntoIterator>,
+    FlattenCompat<I, <I::Item as IntoIterator>::IntoIter>: TrustedLen,
 {
 }
 
@@ -324,6 +310,7 @@ where
 /// Real logic of both `Flatten` and `FlatMap` which simply delegate to
 /// this type.
 #[derive(Clone, Debug)]
+#[unstable(feature = "trusted_len", issue = "37572")]
 struct FlattenCompat<I, U> {
     iter: Fuse<I>,
     frontiter: Option<U>,
@@ -477,6 +464,7 @@ where
     }
 }
 
+#[unstable(feature = "trusted_len", issue = "37572")]
 impl<I, U> Iterator for FlattenCompat<I, U>
 where
     I: Iterator<Item: IntoIterator<IntoIter = U, Item = U::Item>>,
@@ -591,6 +579,7 @@ where
     }
 }
 
+#[unstable(feature = "trusted_len", issue = "37572")]
 impl<I, U> DoubleEndedIterator for FlattenCompat<I, U>
 where
     I: DoubleEndedIterator<Item: IntoIterator<IntoIter = U, Item = U::Item>>,
@@ -660,6 +649,30 @@ where
     }
 }
 
+#[unstable(feature = "trusted_len", issue = "37572")]
+unsafe impl<const N: usize, I, T> TrustedLen
+    for FlattenCompat<I, <[T; N] as IntoIterator>::IntoIter>
+where
+    I: TrustedLen<Item = [T; N]>,
+{
+}
+
+#[unstable(feature = "trusted_len", issue = "37572")]
+unsafe impl<'a, const N: usize, I, T> TrustedLen
+    for FlattenCompat<I, <&'a [T; N] as IntoIterator>::IntoIter>
+where
+    I: TrustedLen<Item = &'a [T; N]>,
+{
+}
+
+#[unstable(feature = "trusted_len", issue = "37572")]
+unsafe impl<'a, const N: usize, I, T> TrustedLen
+    for FlattenCompat<I, <&'a mut [T; N] as IntoIterator>::IntoIter>
+where
+    I: TrustedLen<Item = &'a mut [T; N]>,
+{
+}
+
 trait ConstSizeIntoIterator: IntoIterator {
     // FIXME(#31844): convert to an associated const once specialization supports that
     fn size() -> Option<usize>;
@@ -696,19 +709,6 @@ impl<T, const N: usize> ConstSizeIntoIterator for &mut [T; N] {
     }
 }
 
-#[doc(hidden)]
-#[unstable(feature = "std_internals", issue = "none")]
-// FIXME(#20400): Instead of this helper trait there should be multiple impl TrustedLen for Flatten<>
-//   blocks with different bounds on Iterator::Item but the compiler erroneously considers them overlapping
-pub unsafe trait TrustedConstSize: IntoIterator {}
-
-#[unstable(feature = "std_internals", issue = "none")]
-unsafe impl<T, const N: usize> TrustedConstSize for [T; N] {}
-#[unstable(feature = "std_internals", issue = "none")]
-unsafe impl<T, const N: usize> TrustedConstSize for &'_ [T; N] {}
-#[unstable(feature = "std_internals", issue = "none")]
-unsafe impl<T, const N: usize> TrustedConstSize for &'_ mut [T; N] {}
-
 #[inline]
 fn and_then_or_clear<T, U>(opt: &mut Option<T>, f: impl FnOnce(&mut T) -> Option<U>) -> Option<U> {
     let x = f(opt.as_mut()?);
diff --git a/library/core/src/iter/range.rs b/library/core/src/iter/range.rs
index 37db07429..0171d8981 100644
--- a/library/core/src/iter/range.rs
+++ b/library/core/src/iter/range.rs
@@ -732,12 +732,18 @@ impl<A: Step> Iterator for ops::Range<A> {
     }
 
     #[inline]
-    fn min(mut self) -> Option<A> {
+    fn min(mut self) -> Option<A>
+    where
+        A: Ord,
+    {
         self.next()
     }
 
     #[inline]
-    fn max(mut self) -> Option<A> {
+    fn max(mut self) -> Option<A>
+    where
+        A: Ord,
+    {
         self.next_back()
     }
 
@@ -1158,12 +1164,18 @@ impl<A: Step> Iterator for ops::RangeInclusive<A> {
     }
 
     #[inline]
-    fn min(mut self) -> Option<A> {
+    fn min(mut self) -> Option<A>
+    where
+        A: Ord,
+    {
         self.next()
     }
 
     #[inline]
-    fn max(mut self) -> Option<A> {
+    fn max(mut self) -> Option<A>
+    where
+        A: Ord,
+    {
         self.next_back()
     }
 
diff --git a/library/core/src/iter/sources/empty.rs b/library/core/src/iter/sources/empty.rs
index 617dfd123..243df015f 100644
--- a/library/core/src/iter/sources/empty.rs
+++ b/library/core/src/iter/sources/empty.rs
@@ -81,8 +81,7 @@ impl<T> Clone for Empty<T> {
 // not #[derive] because that adds a Default bound on T,
 // which isn't necessary.
 #[stable(feature = "iter_empty", since = "1.2.0")]
-#[rustc_const_unstable(feature = "const_default_impls", issue = "87864")]
-impl<T> const Default for Empty<T> {
+impl<T> Default for Empty<T> {
     fn default() -> Empty<T> {
         Empty(marker::PhantomData)
     }
diff --git a/library/core/src/iter/traits/collect.rs b/library/core/src/iter/traits/collect.rs
index e099700e3..0675e5635 100644
--- a/library/core/src/iter/traits/collect.rs
+++ b/library/core/src/iter/traits/collect.rs
@@ -95,6 +95,16 @@
 #[stable(feature = "rust1", since = "1.0.0")]
 #[rustc_on_unimplemented(
     on(
+        _Self = "&[{A}]",
+        message = "a slice of type `{Self}` cannot be built since we need to store the elements somewhere",
+        label = "try explicitly collecting into a `Vec<{A}>`",
+    ),
+    on(
+        all(A = "{integer}", any(_Self = "&[{integral}]",)),
+        message = "a slice of type `{Self}` cannot be built since we need to store the elements somewhere",
+        label = "try explicitly collecting into a `Vec<{A}>`",
+    ),
+    on(
         _Self = "[{A}]",
         message = "a slice of type `{Self}` cannot be built since `{Self}` has no definite size",
         label = "try explicitly collecting into a `Vec<{A}>`",
@@ -228,7 +238,6 @@ pub trait FromIterator<A>: Sized {
 #[rustc_diagnostic_item = "IntoIterator"]
 #[rustc_skip_array_during_method_dispatch]
 #[stable(feature = "rust1", since = "1.0.0")]
-#[const_trait]
 pub trait IntoIterator {
     /// The type of the elements being iterated over.
     #[stable(feature = "rust1", since = "1.0.0")]
@@ -264,7 +273,7 @@ pub trait IntoIterator {
 
 #[rustc_const_unstable(feature = "const_intoiterator_identity", issue = "90603")]
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<I: Iterator> const IntoIterator for I {
+impl<I: Iterator> IntoIterator for I {
     type Item = I::Item;
     type IntoIter = I;
 
diff --git a/library/core/src/iter/traits/iterator.rs b/library/core/src/iter/traits/iterator.rs
index 028776042..dabfce144 100644
--- a/library/core/src/iter/traits/iterator.rs
+++ b/library/core/src/iter/traits/iterator.rs
@@ -70,7 +70,6 @@ fn _assert_is_object_safe(_: &dyn Iterator<Item = ()>) {}
 #[doc(notable_trait)]
 #[rustc_diagnostic_item = "Iterator"]
 #[must_use = "iterators are lazy and do nothing unless consumed"]
-#[const_trait]
 pub trait Iterator {
     /// The type of the elements being iterated over.
     #[rustc_diagnostic_item = "IteratorItem"]