From a4d27380b7e4b70f87ff5fb9346077ffa71b622d Mon Sep 17 00:00:00 2001
From: Tatsuyuki Ishi <ishitatsuyuki@gmail.com>
Date: Sat, 25 Feb 2023 16:59:32 +0900
Subject: [PATCH 1/2] binary_heap: Make RebuildOnDrop a common helper.

This helper was written for retain() but will also be useful for extend().
---
 collections/binary_heap/mod.rs | 34 +++++++++++++++++-----------------
 1 file changed, 17 insertions(+), 17 deletions(-)

diff --git a/collections/binary_heap/mod.rs b/collections/binary_heap/mod.rs
index f1d0a30..b6cb791 100644
--- a/collections/binary_heap/mod.rs
+++ b/collections/binary_heap/mod.rs
@@ -400,6 +400,17 @@ impl<T: fmt::Debug> fmt::Debug for BinaryHeap<T> {
     }
 }
 
+struct RebuildOnDrop<'a, T: Ord> {
+    heap: &'a mut BinaryHeap<T>,
+    rebuild_from: usize,
+}
+
+impl<'a, T: Ord> Drop for RebuildOnDrop<'a, T> {
+    fn drop(&mut self) {
+        self.heap.rebuild_tail(self.rebuild_from);
+    }
+}
+
 impl<T: Ord> BinaryHeap<T> {
     /// Creates an empty `BinaryHeap` as a max-heap.
     ///
@@ -851,30 +862,19 @@ impl<T: Ord> BinaryHeap<T> {
     where
         F: FnMut(&T) -> bool,
     {
-        struct RebuildOnDrop<'a, T: Ord> {
-            heap: &'a mut BinaryHeap<T>,
-            first_removed: usize,
-        }
-
-        let mut guard = RebuildOnDrop { first_removed: self.len(), heap: self };
-
+        // rebuild_start will be updated to the first touched element below, and the rebuild will
+        // only be done for the tail.
+        let mut guard = RebuildOnDrop { rebuild_from: self.len(), heap: self };
         let mut i = 0;
+
         guard.heap.data.retain(|e| {
             let keep = f(e);
-            if !keep && i < guard.first_removed {
-                guard.first_removed = i;
+            if !keep && i < guard.rebuild_from {
+                guard.rebuild_from = i;
             }
             i += 1;
             keep
         });
-
-        impl<'a, T: Ord> Drop for RebuildOnDrop<'a, T> {
-            fn drop(&mut self) {
-                // data[..first_removed] is untouched, so we only need to
-                // rebuild the tail:
-                self.heap.rebuild_tail(self.first_removed);
-            }
-        }
     }
 }
 

From cd3ee1904ed4dbe0d91be143bd5d7763dfc056ad Mon Sep 17 00:00:00 2001
From: Tatsuyuki Ishi <ishitatsuyuki@gmail.com>
Date: Sat, 25 Feb 2023 17:03:03 +0900
Subject: [PATCH 2/2] binary_heap: Unify Extend implementation.

Previously the bulk rebuild specialization was only available with Vec, and
for general iterators Extend only provided pre-allocation through reserve().

By using a drop guard, we can safely bulk rebuild even if the iterator may
panic. This allows benefiting from the bulk rebuild optimization without
collecting iterator elements into a Vec beforehand, which would nullify any
performance gains from bulk rebuild.
---
 collections/binary_heap/mod.rs | 36 ++--------------------------------
 1 file changed, 2 insertions(+), 34 deletions(-)

diff --git a/collections/binary_heap/mod.rs b/collections/binary_heap/mod.rs
index b6cb791..7c8cdf6 100644
--- a/collections/binary_heap/mod.rs
+++ b/collections/binary_heap/mod.rs
@@ -154,8 +154,6 @@ use crate::collections::TryReserveError;
 use crate::slice;
 use crate::vec::{self, AsVecIntoIter, Vec};
 
-use super::SpecExtend;
-
 #[cfg(test)]
 mod tests;
 
@@ -1715,7 +1713,8 @@ impl<'a, T> IntoIterator for &'a BinaryHeap<T> {
 impl<T: Ord> Extend<T> for BinaryHeap<T> {
     #[inline]
     fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I) {
-        <Self as SpecExtend<I>>::spec_extend(self, iter);
+        let guard = RebuildOnDrop { rebuild_from: self.len(), heap: self };
+        guard.heap.data.extend(iter);
     }
 
     #[inline]
@@ -1729,37 +1728,6 @@ impl<T: Ord> Extend<T> for BinaryHeap<T> {
     }
 }
 
-impl<T: Ord, I: IntoIterator<Item = T>> SpecExtend<I> for BinaryHeap<T> {
-    default fn spec_extend(&mut self, iter: I) {
-        self.extend_desugared(iter.into_iter());
-    }
-}
-
-impl<T: Ord> SpecExtend<Vec<T>> for BinaryHeap<T> {
-    fn spec_extend(&mut self, ref mut other: Vec<T>) {
-        let start = self.data.len();
-        self.data.append(other);
-        self.rebuild_tail(start);
-    }
-}
-
-impl<T: Ord> SpecExtend<BinaryHeap<T>> for BinaryHeap<T> {
-    fn spec_extend(&mut self, ref mut other: BinaryHeap<T>) {
-        self.append(other);
-    }
-}
-
-impl<T: Ord> BinaryHeap<T> {
-    fn extend_desugared<I: IntoIterator<Item = T>>(&mut self, iter: I) {
-        let iterator = iter.into_iter();
-        let (lower, _) = iterator.size_hint();
-
-        self.reserve(lower);
-
-        iterator.for_each(move |elem| self.push(elem));
-    }
-}
-
 #[stable(feature = "extend_ref", since = "1.2.0")]
 impl<'a, T: 'a + Ord + Copy> Extend<&'a T> for BinaryHeap<T> {
     fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iter: I) {