Add title as fallback for certain sorting modes

Author: KennyLorin

osu.Game.Tests/Visual/SongSelect/BeatmapCarouselFilterSortingTest.cs

@@ -90,6 +90,38 @@ public async Task TestSortingDateSubmitted()
             Assert.That(results.TakeWhile(b => b.BeatmapSet!.DateSubmitted != null).Count(), Is.EqualTo(30), () => "non-missing dates should be at the start");
         }
 
+        [Test]
+        public async Task TestSortByBpmUsesTitleAsTiebreaker()
+        {
+            List<BeatmapSetInfo> beatmapSets = [];
+
+            // 2 sets with same BPM but different titles
+            const int diff_count = 1;
+            {
+                var set = TestResources.CreateTestBeatmapSetInfo(diff_count);
+                set.Beatmaps.ForEach(b =>
+                {
+                    b.BPM = 175;
+                    b.Metadata.Title = "ZZZ";
+                });
+                beatmapSets.Add(set);
+            }
+            {
+                var set = TestResources.CreateTestBeatmapSetInfo(diff_count);
+                set.Beatmaps.ForEach(b =>
+                {
+                    b.BPM = 175;
+                    b.Metadata.Title = "AAA";
+                });
+                beatmapSets.Add(set);
+            }
+
+            var results = (await runSorting(SortMode.BPM, beatmapSets)).ToList();
+
+            Assert.AreEqual("AAA", results[0].Metadata.Title);
+            Assert.AreEqual("ZZZ", results[1].Metadata.Title);
+        }
+
         [Test]
         public async Task TestSortByArtistUsesTitleAsTiebreaker()
         {

osu.Game/Screens/Select/BeatmapCarouselFilterSorting.cs

@@ -115,6 +115,17 @@ private static int compare(BeatmapInfo a, BeatmapInfo b, SortMode sort, bool agg
                     throw new ArgumentOutOfRangeException();
             }
 
+            // For certain sort modes, use title comparison as a fallback
+            // To begin with, I've only added the mode that concerns *me* but I'm sure there are more that could make use of this logic, down for you to decide which to add.
+            if (comparison == 0 && new List<SortMode> { SortMode.BPM }.Contains(sort))
+            {
+                // Review: I'm not sure whether to duplicate the comparing logic for titles or introduce a recursive call.
+                // We have the certainty that we won't go in an infinite recursion since the list in the if's condition excludes the mode that we're recursing on.
+
+                // comparison = OrdinalSortByCaseStringComparer.DEFAULT.Compare(a.BeatmapSet!.Metadata.Title, b.BeatmapSet!.Metadata.Title);
+                comparison = compare(a, b, SortMode.Title, aggregate);
+            }
+
             // If the initial sort could not differentiate, attempt to use DateAdded to order sets in a stable fashion.
             // The directionality of this matches the current SortMode.DateAdded, but we may want to reconsider if that becomes a user decision (ie. asc / desc).
             if (comparison == 0)