Adjust logic to properly list selectable mods

osu.Game/Screens/OnlinePlay/Multiplayer/Match/MultiplayerUserModSelectOverlay.cs

@@ -14,6 +14,7 @@ using osu.Game.Overlays;
 using osu.Game.Overlays.Mods;
 using osu.Game.Rulesets;
 using osu.Game.Rulesets.Mods;
+using osu.Game.Utils;
 
 namespace osu.Game.Screens.OnlinePlay.Multiplayer.Match
 {
@@ -80,7 +81,7 @@ namespace osu.Game.Screens.OnlinePlay.Multiplayer.Match
 
             MultiplayerPlaylistItem currentItem = client.Room.CurrentPlaylistItem;
             Ruleset ruleset = rulesets.GetRuleset(client.LocalUser.RulesetId ?? currentItem.RulesetID)!.CreateInstance();
-            Mod[] allowedMods = currentItem.AllowedMods.Select(m => m.ToMod(ruleset)).ToArray();
+            Mod[] allowedMods = ModUtils.ListUserSelectableFreeMods(client.Room.Settings.MatchType, currentItem.RequiredMods, currentItem.AllowedMods, currentItem.Freestyle, ruleset);
 
             // Update the mod panels to reflect the ones which are valid for selection.
             IsValidMod = m => allowedMods.Any(a => a.GetType() == m.GetType());

osu.Game/Screens/OnlinePlay/Playlists/PlaylistsRoomSubScreen.cs

@@ -551,27 +551,18 @@ namespace osu.Game.Screens.OnlinePlay.Playlists
             updateGameplayState();
         }
 
-        /// <summary>
-        /// Lists the <see cref="Mod"/>s that are valid to be selected for the user mod style.
-        /// </summary>
-        private Mod[] listAllowedMods()
-        {
-            if (SelectedItem.Value == null)
-                return [];
-
-            PlaylistItem item = SelectedItem.Value;
-            RulesetInfo gameplayRuleset = UserRuleset.Value ?? rulesets.GetRuleset(item.RulesetID)!;
-            Ruleset rulesetInstance = gameplayRuleset.CreateInstance();
-
-            return item.AllowedMods.Select(m => m.ToMod(rulesetInstance)).ToArray();
-        }
-
         /// <summary>
         /// Validates the user mod style against the selected item and ruleset style.
         /// </summary>
         private void validateUserMods()
         {
-            Mod[] allowedMods = listAllowedMods();
+            if (SelectedItem.Value == null)
+                return;
+
+            PlaylistItem item = SelectedItem.Value;
+            RulesetInfo gameplayRuleset = UserRuleset.Value ?? rulesets.GetRuleset(item.RulesetID)!;
+            Mod[] allowedMods = ModUtils.ListUserSelectableFreeMods(MatchType.Playlists, item.RequiredMods, item.AllowedMods, item.Freestyle, gameplayRuleset.CreateInstance());
+
             UserMods.Value = UserMods.Value.Where(m => allowedMods.Any(a => m.GetType() == a.GetType())).ToArray();
         }
 
@@ -588,7 +579,7 @@ namespace osu.Game.Screens.OnlinePlay.Playlists
             IBeatmapInfo gameplayBeatmap = UserBeatmap.Value ?? item.Beatmap;
             RulesetInfo gameplayRuleset = UserRuleset.Value ?? rulesets.GetRuleset(item.RulesetID)!;
             Ruleset rulesetInstance = gameplayRuleset.CreateInstance();
-            Mod[] allowedMods = listAllowedMods();
+            Mod[] allowedMods = ModUtils.ListUserSelectableFreeMods(MatchType.Playlists, item.RequiredMods, item.AllowedMods, item.Freestyle, gameplayRuleset.CreateInstance());
 
             // Update global gameplay state to correspond to the new selection.
             // Retrieve the corresponding local beatmap, since we can't directly use the playlist's beatmap info

osu.Game/Utils/ModUtils.cs

@@ -320,5 +320,32 @@ namespace osu.Game.Utils
                     return isRequired ? mod.ValidForMultiplayer : mod.ValidForMultiplayerAsFreeMod;
             }
         }
+
+        /// <summary>
+        /// Given an online listing of mods and the user's preferred ruleset, gathers the mods which are selectable as free mods by the current user.
+        /// </summary>
+        /// <param name="matchType">The type of match being played.</param>
+        /// <param name="requiredMods">The required mods for the playlist item.</param>
+        /// <param name="allowedMods">The allowed mods for the playlist item.</param>
+        /// <param name="freestyle">Whether freestyle is enabled for the playlist item.</param>
+        /// <param name="userRuleset">The user's preferred ruleset, which may differ from the playlist item's selection on freestyle playlist items.</param>
+        public static Mod[] ListUserSelectableFreeMods(MatchType matchType, IEnumerable<APIMod> requiredMods, IEnumerable<APIMod> allowedMods, bool freestyle, Ruleset userRuleset)
+        {
+            if (freestyle)
+            {
+                Mod[] rulesetRequiredMods = requiredMods.Select(m => m.ToMod(userRuleset)).ToArray();
+
+                // In freestyle, the playlist item doesn't provide the allowed mods. Instead, all mods are unconditionally allowed by default.
+                return userRuleset.AllMods.OfType<Mod>()
+                                  // But the mods must still be compatible with the room...
+                                  .Where(m => IsValidModForMatch(m, matchType, false, true))
+                                  // ... And compatible with the required mods listing (this also handles de-duplication).
+                                  .Where(m => CheckCompatibleSet(rulesetRequiredMods.Append(m)))
+                                  .ToArray();
+            }
+
+            // Without freestyle, only the mods specified by the playlist item are valid.
+            return allowedMods.Select(m => m.ToMod(userRuleset)).ToArray();
+        }
     }
 }