From 8f754ffe46bbe30bdfdf94a0027f3e3aaf48fa54 Mon Sep 17 00:00:00 2001
From: Patrick Strawderman <pstrawderman@netflix.com>
Date: Wed, 28 Sep 2022 13:19:50 -0700
Subject: [PATCH] Fix Spliterator implementations for sorted collections

Spliterators returned by CollectSpliterators.indexed and ImmutableSortedSet.spliterator
violated the Spliterator API by not returning null in getComparator when the source
items are naturally sorted. The effect was that sort operations on Streams backed by
these Spliterators were not optimized away, resulting in additional unnecessary sorting.

Fixes #6187.
---
 guava/src/com/google/common/collect/CollectSpliterators.java | 4 ++++
 guava/src/com/google/common/collect/ImmutableSortedSet.java  | 5 +++++
 2 files changed, 9 insertions(+)

diff --git a/guava/src/com/google/common/collect/CollectSpliterators.java b/guava/src/com/google/common/collect/CollectSpliterators.java
index 7d0e82f203a8..b6bb16b8a93e 100644
--- a/guava/src/com/google/common/collect/CollectSpliterators.java
+++ b/guava/src/com/google/common/collect/CollectSpliterators.java
@@ -96,6 +96,10 @@ public int characteristics() {
       @CheckForNull
       public Comparator<? super T> getComparator() {
         if (hasCharacteristics(Spliterator.SORTED)) {
+          if (Ordering.natural().equals(comparator)
+                  || Comparator.naturalOrder().equals(comparator)) {
+            return null;
+          }
           return comparator;
         } else {
           throw new IllegalStateException();
diff --git a/guava/src/com/google/common/collect/ImmutableSortedSet.java b/guava/src/com/google/common/collect/ImmutableSortedSet.java
index 20d007271298..034e9b9795c8 100644
--- a/guava/src/com/google/common/collect/ImmutableSortedSet.java
+++ b/guava/src/com/google/common/collect/ImmutableSortedSet.java
@@ -805,7 +805,12 @@ public boolean tryAdvance(Consumer<? super E> action) {
       }
 
       @Override
+      @CheckForNull
       public Comparator<? super E> getComparator() {
+        if (Ordering.natural().equals(comparator)
+                || Comparator.naturalOrder().equals(comparator)) {
+          return null;
+        }
         return comparator;
       }
     };