btree: use Option's unwrap_unchecked()

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

@@ -11,7 +11,6 @@ use core::ptr;
 use super::borrow::DormantMutRef;
 use super::node::{self, marker, ForceResult::*, Handle, NodeRef, Root};
 use super::search::SearchResult::*;
-use super::unwrap_unchecked;
 
 mod entry;
 pub use entry::{Entry, OccupiedEntry, VacantEntry};
@@ -1386,7 +1385,7 @@ impl<K, V> Drop for IntoIter<K, V> {
 
                 unsafe {
                     let mut node =
-                        unwrap_unchecked(ptr::read(&self.0.front)).into_node().forget_type();
+                        ptr::read(&self.0.front).unwrap_unchecked().into_node().forget_type();
                     while let Some(parent) = node.deallocate_and_ascend() {
                         node = parent.into_node().forget_type();
                     }
@@ -1711,7 +1710,7 @@ impl<'a, K, V> Range<'a, K, V> {
     }
 
     unsafe fn next_unchecked(&mut self) -> (&'a K, &'a V) {
-        unsafe { unwrap_unchecked(self.front.as_mut()).next_unchecked() }
+        unsafe { self.front.as_mut().unwrap_unchecked().next_unchecked() }
     }
 }
 
@@ -1800,7 +1799,7 @@ impl<'a, K, V> DoubleEndedIterator for Range<'a, K, V> {
 
 impl<'a, K, V> Range<'a, K, V> {
     unsafe fn next_back_unchecked(&mut self) -> (&'a K, &'a V) {
-        unsafe { unwrap_unchecked(self.back.as_mut()).next_back_unchecked() }
+        unsafe { self.back.as_mut().unwrap_unchecked().next_back_unchecked() }
     }
 }
 
@@ -1846,7 +1845,7 @@ impl<'a, K, V> RangeMut<'a, K, V> {
     }
 
     unsafe fn next_unchecked(&mut self) -> (&'a K, &'a mut V) {
-        unsafe { unwrap_unchecked(self.front.as_mut()).next_unchecked() }
+        unsafe { self.front.as_mut().unwrap_unchecked().next_unchecked() }
     }
 
     /// Returns an iterator of references over the remaining items.
@@ -1876,7 +1875,7 @@ impl<K, V> FusedIterator for RangeMut<'_, K, V> {}
 
 impl<'a, K, V> RangeMut<'a, K, V> {
     unsafe fn next_back_unchecked(&mut self) -> (&'a K, &'a mut V) {
-        unsafe { unwrap_unchecked(self.back.as_mut()).next_back_unchecked() }
+        unsafe { self.back.as_mut().unwrap_unchecked().next_back_unchecked() }
     }
 }
 

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

@@ -19,22 +19,6 @@ trait Recover<Q: ?Sized> {
     fn replace(&mut self, key: Self::Key) -> Option<Self::Key>;
 }
 
-/// Same purpose as `Option::unwrap` but doesn't always guarantee a panic
-/// if the option contains no value.
-/// SAFETY: the caller must ensure that the option contains a value.
-#[inline(always)]
-pub unsafe fn unwrap_unchecked<T>(val: Option<T>) -> T {
-    val.unwrap_or_else(|| {
-        if cfg!(debug_assertions) {
-            panic!("'unchecked' unwrap on None in BTreeMap");
-        } else {
-            unsafe {
-                core::intrinsics::unreachable();
-            }
-        }
-    })
-}
-
 #[cfg(test)]
 /// XorShiftRng
 struct DeterministicRng {

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

@@ -6,7 +6,6 @@ use core::ptr;
 
 use super::node::{marker, ForceResult::*, Handle, NodeRef};
 use super::search::SearchResult;
-use super::unwrap_unchecked;
 
 /// Finds the leaf edges delimiting a specified range in or underneath a node.
 ///
@@ -310,7 +309,7 @@ macro_rules! def_next_kv_uncheched_dealloc {
                     Err(last_edge) => {
                         unsafe {
                             let parent_edge = last_edge.into_node().deallocate_and_ascend();
-                            unwrap_unchecked(parent_edge).forget_node_type()
+                            parent_edge.unwrap_unchecked().forget_node_type()
                         }
                     }
                 }
@@ -331,7 +330,7 @@ impl<'a, K, V> Handle<NodeRef<marker::Immut<'a>, K, V, marker::Leaf>, marker::Ed
     pub unsafe fn next_unchecked(&mut self) -> (&'a K, &'a V) {
         super::mem::replace(self, |leaf_edge| {
             let kv = leaf_edge.next_kv();
-            let kv = unsafe { unwrap_unchecked(kv.ok()) };
+            let kv = unsafe { kv.ok().unwrap_unchecked() };
             (kv.next_leaf_edge(), kv.into_kv())
         })
     }
@@ -344,7 +343,7 @@ impl<'a, K, V> Handle<NodeRef<marker::Immut<'a>, K, V, marker::Leaf>, marker::Ed
     pub unsafe fn next_back_unchecked(&mut self) -> (&'a K, &'a V) {
         super::mem::replace(self, |leaf_edge| {
             let kv = leaf_edge.next_back_kv();
-            let kv = unsafe { unwrap_unchecked(kv.ok()) };
+            let kv = unsafe { kv.ok().unwrap_unchecked() };
             (kv.next_back_leaf_edge(), kv.into_kv())
         })
     }
@@ -359,7 +358,7 @@ impl<'a, K, V> Handle<NodeRef<marker::ValMut<'a>, K, V, marker::Leaf>, marker::E
     pub unsafe fn next_unchecked(&mut self) -> (&'a K, &'a mut V) {
         let kv = super::mem::replace(self, |leaf_edge| {
             let kv = leaf_edge.next_kv();
-            let kv = unsafe { unwrap_unchecked(kv.ok()) };
+            let kv = unsafe { kv.ok().unwrap_unchecked() };
             (unsafe { ptr::read(&kv) }.next_leaf_edge(), kv)
         });
         // Doing this last is faster, according to benchmarks.
@@ -374,7 +373,7 @@ impl<'a, K, V> Handle<NodeRef<marker::ValMut<'a>, K, V, marker::Leaf>, marker::E
     pub unsafe fn next_back_unchecked(&mut self) -> (&'a K, &'a mut V) {
         let kv = super::mem::replace(self, |leaf_edge| {
             let kv = leaf_edge.next_back_kv();
-            let kv = unsafe { unwrap_unchecked(kv.ok()) };
+            let kv = unsafe { kv.ok().unwrap_unchecked() };
             (unsafe { ptr::read(&kv) }.next_back_leaf_edge(), kv)
         });
         // Doing this last is faster, according to benchmarks.

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

@@ -1,6 +1,5 @@
 use super::map::MIN_LEN;
 use super::node::{marker, ForceResult::*, Handle, LeftOrRight::*, NodeRef};
-use super::unwrap_unchecked;
 
 impl<'a, K: 'a, V: 'a> Handle<NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal>, marker::KV> {
     /// Removes a key-value pair from the tree, and returns that pair, as well as
@@ -77,12 +76,12 @@ impl<'a, K: 'a, V: 'a> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Internal>,
         // the element we were asked to remove. Prefer the left adjacent KV,
         // for the reasons listed in `choose_parent_kv`.
         let left_leaf_kv = self.left_edge().descend().last_leaf_edge().left_kv();
-        let left_leaf_kv = unsafe { unwrap_unchecked(left_leaf_kv.ok()) };
+        let left_leaf_kv = unsafe { left_leaf_kv.ok().unwrap_unchecked() };
         let (left_kv, left_hole) = left_leaf_kv.remove_leaf_kv(handle_emptied_internal_root);
 
         // The internal node may have been stolen from or merged. Go back right
         // to find where the original KV ended up.
-        let mut internal = unsafe { unwrap_unchecked(left_hole.next_kv().ok()) };
+        let mut internal = unsafe { left_hole.next_kv().ok().unwrap_unchecked() };
         let old_kv = internal.replace_kv(left_kv.0, left_kv.1);
         let pos = internal.next_leaf_edge();
         (old_kv, pos)

library/alloc/src/lib.rs

@@ -111,6 +111,7 @@
 #![feature(nll)]
 #![feature(nonnull_slice_from_raw_parts)]
 #![feature(auto_traits)]
+#![feature(option_result_unwrap_unchecked)]
 #![feature(or_patterns)]
 #![feature(pattern)]
 #![feature(ptr_internals)]