Rollup merge of rust-lang#61363 - lzutao:stabilize-iter_nth_back, r=C…

…entril

Stabilize iter_nth_back feature

FCP done in rust-lang#56995 (comment)

Closes rust-lang#56995

r? @Centril

src/liballoc/lib.rs

@@ -112,7 +112,6 @@
 #![feature(maybe_uninit_extra, maybe_uninit_slice, maybe_uninit_array)]
 #![feature(alloc_layout_extra)]
 #![feature(try_trait)]
-#![feature(iter_nth_back)]
 
 // Allow testing this library
 

src/libcore/iter/traits/double_ended.rs

@@ -88,15 +88,13 @@ pub trait DoubleEndedIterator: Iterator {
     /// Basic usage:
     ///
     /// ```
-    /// #![feature(iter_nth_back)]
     /// let a = [1, 2, 3];
     /// assert_eq!(a.iter().nth_back(2), Some(&1));
     /// ```
     ///
     /// Calling `nth_back()` multiple times doesn't rewind the iterator:
     ///
     /// ```
-    /// #![feature(iter_nth_back)]
     /// let a = [1, 2, 3];
     ///
     /// let mut iter = a.iter();
@@ -108,12 +106,11 @@ pub trait DoubleEndedIterator: Iterator {
     /// Returning `None` if there are less than `n + 1` elements:
     ///
     /// ```
-    /// #![feature(iter_nth_back)]
     /// let a = [1, 2, 3];
     /// assert_eq!(a.iter().nth_back(10), None);
     /// ```
     #[inline]
-    #[unstable(feature = "iter_nth_back", issue = "56995")]
+    #[stable(feature = "iter_nth_back", since = "1.37.0")]
     fn nth_back(&mut self, mut n: usize) -> Option<Self::Item> {
         for x in self.rev() {
             if n == 0 { return Some(x) }

src/libcore/tests/lib.rs

@@ -10,7 +10,6 @@
 #![feature(fmt_internals)]
 #![feature(hashmap_internals)]
 #![feature(is_sorted)]
-#![feature(iter_nth_back)]
 #![feature(iter_once_with)]
 #![feature(pattern)]
 #![feature(range_is_empty)]