From 3f5c113394e9c07505d3bc83e95753a2dddf68ca Mon Sep 17 00:00:00 2001
From: triacontakai <31161627+triacontakai@users.noreply.github.com>
Date: Thu, 7 May 2026 02:59:54 -0400
Subject: [PATCH] Fix non-default mod settings allowing for duplicate freestyle
 mod selection in multiplayer (#37646)
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Fixes a bug that allowed for selecting the same mod twice in multiplayer
if the playlist entry has non-default settings for a required mod.
This happens due to a strict equality mod check in the mod set
compatibility check function, which only considers mods duplicates if
their settings are exactly the same. Replacing with a more lenient
`Type` check fixes this.

Adds a regression test for this behavior

Fixes https://github.com/ppy/osu/issues/37625.

---------

Co-authored-by: Bartłomiej Dach <dach.bartlomiej@gmail.com>
---
 osu.Game.Tests/Mods/ModUtilsTest.cs           | 19 +++++++++++++
 .../TestSceneMultiplayerMatchSubScreen.cs     | 27 +++++++++++++++++++
 osu.Game/Utils/ModUtils.cs                    |  2 +-
 3 files changed, 47 insertions(+), 1 deletion(-)

diff --git a/osu.Game.Tests/Mods/ModUtilsTest.cs b/osu.Game.Tests/Mods/ModUtilsTest.cs
index b05b4c00b9..f0f08e5a31 100644
--- a/osu.Game.Tests/Mods/ModUtilsTest.cs
+++ b/osu.Game.Tests/Mods/ModUtilsTest.cs
@@ -7,8 +7,10 @@ using System.Linq;
 using Moq;
 using NUnit.Framework;
 using NUnit.Framework.Legacy;
+using osu.Framework.Bindables;
 using osu.Framework.Extensions.TypeExtensions;
 using osu.Framework.Localisation;
+using osu.Game.Configuration;
 using osu.Game.Online.Rooms;
 using osu.Game.Rulesets;
 using osu.Game.Rulesets.Catch;
@@ -33,6 +35,17 @@ namespace osu.Game.Tests.Mods
             Assert.That(invalid, Is.EquivalentTo(new[] { mod.Object }));
         }
 
+        [Test]
+        public void TestModIsNotCompatibleWithItselfEvenIfSettingsDiffer()
+        {
+            var mod1 = new Mock<CustomMod3>();
+            var mod2 = new Mock<CustomMod3>();
+            mod2.Setup(m => m.Setting).Returns(new BindableBool(true));
+
+            Assert.That(ModUtils.CheckCompatibleSet(new[] { mod1.Object, mod2.Object }, out var invalid), Is.False);
+            Assert.That(invalid, Is.EquivalentTo(new[] { mod2.Object }));
+        }
+
         [Test]
         public void TestModIsCompatibleByItself()
         {
@@ -397,6 +410,12 @@ namespace osu.Game.Tests.Mods
         {
         }
 
+        public abstract class CustomMod3 : Mod, IModCompatibilitySpecification
+        {
+            [SettingSource("Setting")]
+            public virtual BindableBool Setting { get; } = new BindableBool();
+        }
+
         private class InvalidMultiplayerMod : Mod
         {
             public override string Name => string.Empty;
diff --git a/osu.Game.Tests/Visual/Multiplayer/TestSceneMultiplayerMatchSubScreen.cs b/osu.Game.Tests/Visual/Multiplayer/TestSceneMultiplayerMatchSubScreen.cs
index 379a589ca9..7a72178645 100644
--- a/osu.Game.Tests/Visual/Multiplayer/TestSceneMultiplayerMatchSubScreen.cs
+++ b/osu.Game.Tests/Visual/Multiplayer/TestSceneMultiplayerMatchSubScreen.cs
@@ -330,6 +330,33 @@ namespace osu.Game.Tests.Visual.Multiplayer
             AddAssert("score multiplier = 1.20", () => this.ChildrenOfType<RankingInformationDisplay>().Single().ModMultiplier.Value, () => Is.EqualTo(1.2).Within(0.01));
         }
 
+        [Test]
+        public void TestModSelectOverlayNonDefaultSettings()
+        {
+            AddStep("add playlist item", () =>
+            {
+                room.Playlist =
+                [
+                    new PlaylistItem(new TestBeatmap(new OsuRuleset().RulesetInfo).BeatmapInfo)
+                    {
+                        RulesetID = new OsuRuleset().RulesetInfo.OnlineID,
+                        RequiredMods =
+                        [
+                            new APIMod(new OsuModSuddenDeath { FailOnSliderTail = { Value = true } }),
+                        ],
+                        AllowedMods = [],
+                        Freestyle = true
+                    }
+                ];
+            });
+            ClickButtonWhenEnabled<MultiplayerMatchSettingsOverlay.CreateOrUpdateButton>();
+
+            AddUntilStep("wait for join", () => RoomJoined);
+
+            ClickButtonWhenEnabled<UserModSelectButton>();
+            AddAssert("sudden death not visible", () => this.ChildrenOfType<MultiplayerUserModSelectOverlay>().Single().ChildrenOfType<ModPanel>().Single(m => m.Mod is ModSuddenDeath).Visible == false);
+        }
+
         [Test]
         public void TestChangeSettingsButtonVisibleForHost()
         {
diff --git a/osu.Game/Utils/ModUtils.cs b/osu.Game/Utils/ModUtils.cs
index e944b188f1..01b0aab46b 100644
--- a/osu.Game/Utils/ModUtils.cs
+++ b/osu.Game/Utils/ModUtils.cs
@@ -63,7 +63,7 @@ namespace osu.Game.Utils
                 {
                     var m = mods[j];
 
-                    if (candidate.Equals(m))
+                    if (candidate.GetType() == m.GetType())
                     {
                         invalidMods ??= new List<Mod>();
                         invalidMods.Add(m);