From 6d0563664557279ad15df82a9eced806e1c44adb Mon Sep 17 00:00:00 2001
From: Yotam Ofek <yotam.ofek@gmail.com>
Date: Thu, 27 Nov 2025 14:47:54 +0200
Subject: [PATCH] Add `impl TrustedLen` on `BTree{Map,Set}` iterators

---
 library/alloc/src/collections/btree/map.rs | 26 +++++++++++++++++++++-
 library/alloc/src/collections/btree/set.rs | 12 +++++++++-
 2 files changed, 36 insertions(+), 2 deletions(-)

diff --git a/library/alloc/src/collections/btree/map.rs b/library/alloc/src/collections/btree/map.rs
index 766f4589177a8..71ed8ca1468a7 100644
--- a/library/alloc/src/collections/btree/map.rs
+++ b/library/alloc/src/collections/btree/map.rs
@@ -3,7 +3,7 @@ use core::cmp::Ordering;
 use core::error::Error;
 use core::fmt::{self, Debug};
 use core::hash::{Hash, Hasher};
-use core::iter::FusedIterator;
+use core::iter::{FusedIterator, TrustedLen};
 use core::marker::PhantomData;
 use core::mem::{self, ManuallyDrop};
 use core::ops::{Bound, Index, RangeBounds};
@@ -1624,6 +1624,9 @@ impl<K, V> ExactSizeIterator for Iter<'_, K, V> {
     }
 }
 
+#[unstable(feature = "trusted_len", issue = "37572")]
+unsafe impl<K, V> TrustedLen for Iter<'_, K, V> {}
+
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<K, V> Clone for Iter<'_, K, V> {
     fn clone(&self) -> Self {
@@ -1696,6 +1699,9 @@ impl<K, V> ExactSizeIterator for IterMut<'_, K, V> {
     }
 }
 
+#[unstable(feature = "trusted_len", issue = "37572")]
+unsafe impl<K, V> TrustedLen for IterMut<'_, K, V> {}
+
 #[stable(feature = "fused", since = "1.26.0")]
 impl<K, V> FusedIterator for IterMut<'_, K, V> {}
 
@@ -1817,6 +1823,9 @@ impl<K, V, A: Allocator + Clone> ExactSizeIterator for IntoIter<K, V, A> {
     }
 }
 
+#[unstable(feature = "trusted_len", issue = "37572")]
+unsafe impl<K, V, A: Allocator + Clone> TrustedLen for IntoIter<K, V, A> {}
+
 #[stable(feature = "fused", since = "1.26.0")]
 impl<K, V, A: Allocator + Clone> FusedIterator for IntoIter<K, V, A> {}
 
@@ -1865,6 +1874,9 @@ impl<K, V> ExactSizeIterator for Keys<'_, K, V> {
     }
 }
 
+#[unstable(feature = "trusted_len", issue = "37572")]
+unsafe impl<K, V> TrustedLen for Keys<'_, K, V> {}
+
 #[stable(feature = "fused", since = "1.26.0")]
 impl<K, V> FusedIterator for Keys<'_, K, V> {}
 
@@ -1920,6 +1932,9 @@ impl<K, V> ExactSizeIterator for Values<'_, K, V> {
     }
 }
 
+#[unstable(feature = "trusted_len", issue = "37572")]
+unsafe impl<K, V> TrustedLen for Values<'_, K, V> {}
+
 #[stable(feature = "fused", since = "1.26.0")]
 impl<K, V> FusedIterator for Values<'_, K, V> {}
 
@@ -2160,6 +2175,9 @@ impl<K, V> ExactSizeIterator for ValuesMut<'_, K, V> {
     }
 }
 
+#[unstable(feature = "trusted_len", issue = "37572")]
+unsafe impl<K, V> TrustedLen for ValuesMut<'_, K, V> {}
+
 #[stable(feature = "fused", since = "1.26.0")]
 impl<K, V> FusedIterator for ValuesMut<'_, K, V> {}
 
@@ -2222,6 +2240,9 @@ impl<K, V, A: Allocator + Clone> ExactSizeIterator for IntoKeys<K, V, A> {
     }
 }
 
+#[unstable(feature = "trusted_len", issue = "37572")]
+unsafe impl<K, V, A: Allocator + Clone> TrustedLen for IntoKeys<K, V, A> {}
+
 #[stable(feature = "map_into_keys_values", since = "1.54.0")]
 impl<K, V, A: Allocator + Clone> FusedIterator for IntoKeys<K, V, A> {}
 
@@ -2273,6 +2294,9 @@ impl<K, V, A: Allocator + Clone> ExactSizeIterator for IntoValues<K, V, A> {
     }
 }
 
+#[unstable(feature = "trusted_len", issue = "37572")]
+unsafe impl<K, V, A: Allocator + Clone> TrustedLen for IntoValues<K, V, A> {}
+
 #[stable(feature = "map_into_keys_values", since = "1.54.0")]
 impl<K, V, A: Allocator + Clone> FusedIterator for IntoValues<K, V, A> {}
 
diff --git a/library/alloc/src/collections/btree/set.rs b/library/alloc/src/collections/btree/set.rs
index 28d26699d7d2c..fd27e87b1f470 100644
--- a/library/alloc/src/collections/btree/set.rs
+++ b/library/alloc/src/collections/btree/set.rs
@@ -3,7 +3,7 @@ use core::cmp::Ordering::{self, Equal, Greater, Less};
 use core::cmp::{max, min};
 use core::fmt::{self, Debug};
 use core::hash::{Hash, Hasher};
-use core::iter::{FusedIterator, Peekable};
+use core::iter::{FusedIterator, Peekable, TrustedLen};
 use core::mem::ManuallyDrop;
 use core::ops::{BitAnd, BitOr, BitXor, Bound, RangeBounds, Sub};
 
@@ -1753,6 +1753,7 @@ impl<T> Clone for Iter<'_, T> {
         Iter { iter: self.iter.clone() }
     }
 }
+
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<'a, T> Iterator for Iter<'a, T> {
     type Item = &'a T;
@@ -1783,12 +1784,14 @@ impl<'a, T> Iterator for Iter<'a, T> {
         self.next_back()
     }
 }
+
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<'a, T> DoubleEndedIterator for Iter<'a, T> {
     fn next_back(&mut self) -> Option<&'a T> {
         self.iter.next_back()
     }
 }
+
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T> ExactSizeIterator for Iter<'_, T> {
     fn len(&self) -> usize {
@@ -1796,6 +1799,9 @@ impl<T> ExactSizeIterator for Iter<'_, T> {
     }
 }
 
+#[unstable(feature = "trusted_len", issue = "37572")]
+unsafe impl<T> TrustedLen for Iter<'_, T> {}
+
 #[stable(feature = "fused", since = "1.26.0")]
 impl<T> FusedIterator for Iter<'_, T> {}
 
@@ -1832,6 +1838,7 @@ impl<T, A: Allocator + Clone> DoubleEndedIterator for IntoIter<T, A> {
         self.iter.next_back().map(|(k, _)| k)
     }
 }
+
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T, A: Allocator + Clone> ExactSizeIterator for IntoIter<T, A> {
     fn len(&self) -> usize {
@@ -1839,6 +1846,9 @@ impl<T, A: Allocator + Clone> ExactSizeIterator for IntoIter<T, A> {
     }
 }
 
+#[unstable(feature = "trusted_len", issue = "37572")]
+unsafe impl<T, A: Allocator + Clone> TrustedLen for IntoIter<T, A> {}
+
 #[stable(feature = "fused", since = "1.26.0")]
 impl<T, A: Allocator + Clone> FusedIterator for IntoIter<T, A> {}