Manually implement Debug for BTreeMap::{IntoKeys,IntoValues} structs

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

@@ -298,14 +298,23 @@ pub struct IntoIter<K, V> {
     length: usize,
 }
 
-#[stable(feature = "collection_debug", since = "1.17.0")]
-impl<K: fmt::Debug, V: fmt::Debug> fmt::Debug for IntoIter<K, V> {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+impl<K, V> IntoIter<K, V> {
+    /// Returns an iterator of references over the remaining items.
+    #[inline]
+    pub(super) fn iter(&self) -> Iter<'_, K, V> {
         let range = Range {
             front: self.front.as_ref().map(|f| f.reborrow()),
             back: self.back.as_ref().map(|b| b.reborrow()),
         };
-        f.debug_list().entries(range).finish()
+
+        Iter { range: range, length: self.length }
+    }
+}
+
+#[stable(feature = "collection_debug", since = "1.17.0")]
+impl<K: fmt::Debug, V: fmt::Debug> fmt::Debug for IntoIter<K, V> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_list().entries(self.iter()).finish()
     }
 }
 
@@ -364,11 +373,17 @@ pub struct ValuesMut<'a, K: 'a, V: 'a> {
 ///
 /// [`into_keys`]: BTreeMap::into_keys
 #[unstable(feature = "map_into_keys_values", issue = "75294")]
-#[derive(Debug)]
 pub struct IntoKeys<K, V> {
     inner: IntoIter<K, V>,
 }
 
+#[unstable(feature = "map_into_keys_values", issue = "75294")]
+impl<K: fmt::Debug, V> fmt::Debug for IntoKeys<K, V> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_list().entries(self.inner.iter().map(|(key, _)| key)).finish()
+    }
+}
+
 /// An owning iterator over the values of a `BTreeMap`.
 ///
 /// This `struct` is created by the [`into_values`] method on [`BTreeMap`].
@@ -376,11 +391,17 @@ pub struct IntoKeys<K, V> {
 ///
 /// [`into_values`]: BTreeMap::into_values
 #[unstable(feature = "map_into_keys_values", issue = "75294")]
-#[derive(Debug)]
 pub struct IntoValues<K, V> {
     inner: IntoIter<K, V>,
 }
 
+#[unstable(feature = "map_into_keys_values", issue = "75294")]
+impl<K, V: fmt::Debug> fmt::Debug for IntoValues<K, V> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_list().entries(self.inner.iter().map(|(_, val)| val)).finish()
+    }
+}
+
 /// An iterator over a sub-range of entries in a `BTreeMap`.
 ///
 /// This `struct` is created by the [`range`] method on [`BTreeMap`]. See its