Add negative implementation of Iterator for [&[mut]] Box<[T; N], A> and [T; N]

They'll be needed for `IntoIterator` impls.

Author: WaffleLapkin

library/alloc/src/boxed/iter.rs

@@ -192,3 +192,18 @@ impl<'a> FromIterator<Cow<'a, str>> for Box<str> {
         String::from_iter(iter).into_boxed_str()
     }
 }
+
+/// This implementation is required to make sure that the `Box<[I; N]>: IntoIterator`
+/// implementation doesn't overlap with `IntoIterator for T where T: Iterator` blanket.
+#[stable(feature = "boxed_array_value_iter", since = "CURRENT_RUSTC_VERSION")]
+impl<I, const N: usize, A: Allocator> !Iterator for Box<[I; N], A> {}
+
+/// This implementation is required to make sure that the `&Box<[I; N]>: IntoIterator`
+/// implementation doesn't overlap with `IntoIterator for T where T: Iterator` blanket.
+#[stable(feature = "boxed_array_value_iter", since = "CURRENT_RUSTC_VERSION")]
+impl<'a, const N: usize, I, A: Allocator> !Iterator for &'a Box<[I; N], A> {}
+
+/// This implementation is required to make sure that the `&mut Box<[I; N]>: IntoIterator`
+/// implementation doesn't overlap with `IntoIterator for T where T: Iterator` blanket.
+#[stable(feature = "boxed_array_value_iter", since = "CURRENT_RUSTC_VERSION")]
+impl<'a, const N: usize, I, A: Allocator> !Iterator for &'a mut Box<[I; N], A> {}

library/core/src/array/iter.rs

@@ -34,6 +34,9 @@ impl<T, const N: usize> IntoIter<T, N> {
     }
 }
 
+#[stable(feature = "boxed_array_value_iter", since = "CURRENT_RUSTC_VERSION")]
+impl<T, const N: usize> !Iterator for [T; N] {}
+
 // Note: the `#[rustc_skip_during_method_dispatch(array)]` on `trait IntoIterator`
 // hides this implementation from explicit `.into_iter()` calls on editions < 2021,
 // so those calls will still resolve to the slice implementation, by reference.