Stabilize iter::successors

FCP: rust-lang#58045 (comment)

Author: SimonSapin

src/libcore/iter/mod.rs

@@ -327,7 +327,9 @@ pub use self::sources::{Once, once};
 #[unstable(feature = "iter_once_with", issue = "57581")]
 pub use self::sources::{OnceWith, once_with};
 #[unstable(feature = "iter_unfold", issue = "55977")]
-pub use self::sources::{FromFn, from_fn, Successors, successors};
+pub use self::sources::{FromFn, from_fn};
+#[stable(feature = "iter_successors", since = "1.34.0")]
+pub use self::sources::{Successors, successors};
 
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use self::traits::{FromIterator, IntoIterator, DoubleEndedIterator, Extend};

src/libcore/iter/sources.rs

@@ -572,13 +572,12 @@ impl<F> fmt::Debug for FromFn<F> {
 /// and calls the given `FnMut(&T) -> Option<T>` closure to compute each item’s successor.
 ///
 /// ```
-/// #![feature(iter_unfold)]
 /// use std::iter::successors;
 ///
 /// let powers_of_10 = successors(Some(1_u16), |n| n.checked_mul(10));
 /// assert_eq!(powers_of_10.collect::<Vec<_>>(), &[1, 10, 100, 1_000, 10_000]);
 /// ```
-#[unstable(feature = "iter_unfold", issue = "55977")]
+#[stable(feature = "iter_successors", since = "1.34.0")]
 pub fn successors<T, F>(first: Option<T>, succ: F) -> Successors<T, F>
     where F: FnMut(&T) -> Option<T>
 {
@@ -598,13 +597,13 @@ pub fn successors<T, F>(first: Option<T>, succ: F) -> Successors<T, F>
 ///
 /// [`successors`]: fn.successors.html
 #[derive(Clone)]
-#[unstable(feature = "iter_unfold", issue = "55977")]
+#[stable(feature = "iter_successors", since = "1.34.0")]
 pub struct Successors<T, F> {
     next: Option<T>,
     succ: F,
 }
 
-#[unstable(feature = "iter_unfold", issue = "55977")]
+#[stable(feature = "iter_successors", since = "1.34.0")]
 impl<T, F> Iterator for Successors<T, F>
     where F: FnMut(&T) -> Option<T>
 {
@@ -628,12 +627,12 @@ impl<T, F> Iterator for Successors<T, F>
     }
 }
 
-#[unstable(feature = "iter_unfold", issue = "55977")]
+#[stable(feature = "iter_successors", since = "1.34.0")]
 impl<T, F> FusedIterator for Successors<T, F>
     where F: FnMut(&T) -> Option<T>
 {}
 
-#[unstable(feature = "iter_unfold", issue = "55977")]
+#[stable(feature = "iter_successors", since = "1.34.0")]
 impl<T: fmt::Debug, F> fmt::Debug for Successors<T, F> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         f.debug_struct("Successors")