From 68504e96391ae8cb7dcd04c81cd8ffcfd4976717 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bart=C5=82omiej=20Dach?= <dach.bartlomiej@gmail.com>
Date: Fri, 30 May 2025 11:06:44 +0200
Subject: [PATCH 1/2] Add failing test case

---
 .../Visual/SongSelectV2/TestSceneBeatmapCarousel.cs | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/osu.Game.Tests/Visual/SongSelectV2/TestSceneBeatmapCarousel.cs b/osu.Game.Tests/Visual/SongSelectV2/TestSceneBeatmapCarousel.cs
index 56351eed97..616748a9d5 100644
--- a/osu.Game.Tests/Visual/SongSelectV2/TestSceneBeatmapCarousel.cs
+++ b/osu.Game.Tests/Visual/SongSelectV2/TestSceneBeatmapCarousel.cs
@@ -6,9 +6,11 @@ using System.Collections.Generic;
 using System.Linq;
 using System.Threading.Tasks;
 using NUnit.Framework;
+using osu.Framework.Testing;
 using osu.Framework.Utils;
 using osu.Game.Beatmaps;
 using osu.Game.Screens.Select.Filter;
+using osu.Game.Screens.SelectV2;
 using osu.Game.Tests.Resources;
 
 namespace osu.Game.Tests.Visual.SongSelectV2
@@ -116,5 +118,16 @@ namespace osu.Game.Tests.Visual.SongSelectV2
 
             AddStep("add all beatmaps", () => BeatmapSets.AddRange(generated));
         }
+
+        [Test]
+        public void TestSingleItemDisplayed()
+        {
+            CreateCarousel();
+            RemoveAllBeatmaps();
+
+            SortAndGroupBy(SortMode.Difficulty, GroupMode.NoGrouping);
+            AddBeatmaps(1, fixedDifficultiesPerSet: 1);
+            AddUntilStep("single item is shown", () => this.ChildrenOfType<PanelBeatmapStandalone>().Count(), () => Is.EqualTo(1));
+        }
     }
 }

From 2d900c55cfbd3ac99f5c21ce2b0b509ed6e3e20d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bart=C5=82omiej=20Dach?= <dach.bartlomiej@gmail.com>
Date: Fri, 30 May 2025 11:15:15 +0200
Subject: [PATCH 2/2] SongSelectV2: Fix carousel not displaying anything if
 there is only one panel to display

If there is only one panel to display, a `DisplayRange` of (0, 0) is
*very much* valid.
---
 osu.Game/Graphics/Carousel/Carousel.cs | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/osu.Game/Graphics/Carousel/Carousel.cs b/osu.Game/Graphics/Carousel/Carousel.cs
index 9da4d0e187..9646c86dd6 100644
--- a/osu.Game/Graphics/Carousel/Carousel.cs
+++ b/osu.Game/Graphics/Carousel/Carousel.cs
@@ -743,6 +743,9 @@ namespace osu.Game.Graphics.Carousel
         {
             Debug.Assert(carouselItems != null);
 
+            if (carouselItems.Count == 0)
+                return DisplayRange.EMPTY;
+
             // Find index range of all items that should be on-screen
             carouselBoundsItem.CarouselYPosition = visibleUpperBound - DistanceOffscreenToPreload;
             int firstIndex = carouselItems.BinarySearch(carouselBoundsItem);
@@ -762,7 +765,7 @@ namespace osu.Game.Graphics.Carousel
         {
             Debug.Assert(carouselItems != null);
 
-            List<CarouselItem> toDisplay = range.Last - range.First == 0
+            List<CarouselItem> toDisplay = range == DisplayRange.EMPTY
                 ? new List<CarouselItem>()
                 : carouselItems.GetRange(range.First, range.Last - range.First + 1);
 
@@ -881,7 +884,10 @@ namespace osu.Game.Graphics.Carousel
         /// <param name="Index">The index of the selection as of the last run of <see cref="Carousel{T}.refreshAfterSelection"/>. May be null if selection is not present as an item, or if <see cref="Carousel{T}.refreshAfterSelection"/> has not been run yet.</param>
         private record Selection(object? Model = null, CarouselItem? CarouselItem = null, double? YPosition = null, int? Index = null);
 
-        private record DisplayRange(int First, int Last);
+        private record DisplayRange(int First, int Last)
+        {
+            public static readonly DisplayRange EMPTY = new DisplayRange(-1, -1);
+        }
 
         /// <summary>
         /// Implementation of scroll container which handles very large vertical lists by internally using <c>double</c> precision