Convert to extension method to avoid recursive calls

osu.Desktop/DiscordRichPresence.cs

@@ -10,6 +10,7 @@ using osu.Framework.Bindables;
 using osu.Framework.Graphics;
 using osu.Framework.Logging;
 using osu.Game.Configuration;
+using osu.Game.Extensions;
 using osu.Game.Online.API;
 using osu.Game.Online.API.Requests.Responses;
 using osu.Game.Rulesets;
@@ -108,7 +109,7 @@ namespace osu.Desktop
                 presence.Assets.LargeImageText = $"{user.Value.Username}" + (user.Value.Statistics?.GlobalRank > 0 ? $" (rank #{user.Value.Statistics.GlobalRank:N0})" : string.Empty);
 
             // update ruleset
-            presence.Assets.SmallImageKey = ruleset.Value.IsLegacyRuleset ? $"mode_{ruleset.Value.OnlineID}" : "mode_custom";
+            presence.Assets.SmallImageKey = ruleset.Value.IsLegacyRuleset() ? $"mode_{ruleset.Value.OnlineID}" : "mode_custom";
             presence.Assets.SmallImageText = ruleset.Value.Name;
 
             client.SetPresence(presence);

osu.Game/Beatmaps/DifficultyRecommender.cs

@@ -9,6 +9,7 @@ using osu.Framework.Allocation;
 using osu.Framework.Bindables;
 using osu.Framework.Extensions.IEnumerableExtensions;
 using osu.Framework.Graphics;
+using osu.Game.Extensions;
 using osu.Game.Online.API;
 using osu.Game.Online.API.Requests;
 using osu.Game.Rulesets;
@@ -83,7 +84,7 @@ namespace osu.Game.Beatmaps
             requestedUserId = api.LocalUser.Value.Id;
 
             // only query API for built-in rulesets
-            rulesets.AvailableRulesets.Where(ruleset => ruleset.IsLegacyRuleset).ForEach(rulesetInfo =>
+            rulesets.AvailableRulesets.Where(ruleset => ruleset.IsLegacyRuleset()).ForEach(rulesetInfo =>
             {
                 var req = new GetUserRequest(api.LocalUser.Value.Id, rulesetInfo);
 

osu.Game/Extensions/ModelExtensions.cs

@@ -72,6 +72,11 @@ namespace osu.Game.Extensions
             return result;
         }
 
+        /// <summary>
+        /// Check whether this <see cref="IRulesetInfo"/>'s online ID is within the range that defines it as a legacy ruleset (ie. either osu!, osu!taiko, osu!catch or osu!mania).
+        /// </summary>
+        public static bool IsLegacyRuleset(this IRulesetInfo ruleset) => ruleset.OnlineID >= 0 && ruleset.OnlineID <= ILegacyRuleset.MAX_LEGACY_RULESET_ID;
+
         /// <summary>
         /// Check whether the online ID of two <see cref="IBeatmapSetInfo"/>s match.
         /// </summary>

osu.Game/Rulesets/IRulesetInfo.cs

@@ -29,10 +29,5 @@ namespace osu.Game.Rulesets
         string InstantiationInfo { get; }
 
         Ruleset CreateInstance();
-
-        /// <summary>
-        /// Whether this ruleset's online ID is within the range that defines it as a legacy ruleset (ie. either osu!, osu!taiko, osu!catch or osu!mania).
-        /// </summary>
-        public bool IsLegacyRuleset => OnlineID >= 0 && OnlineID <= ILegacyRuleset.MAX_LEGACY_RULESET_ID;
     }
 }

osu.Game/Rulesets/RulesetInfo.cs

@@ -91,11 +91,6 @@ namespace osu.Game.Rulesets
             Available = Available
         };
 
-        /// <summary>
-        /// Whether this ruleset's online ID is within the range that defines it as a legacy ruleset (ie. either osu!, osu!taiko, osu!catch or osu!mania).
-        /// </summary>
-        public bool IsLegacyRuleset => ((IRulesetInfo)this).IsLegacyRuleset;
-
         public Ruleset CreateInstance()
         {
             if (!Available)

osu.Game/Screens/Play/SoloPlayer.cs

@@ -4,6 +4,7 @@
 using System;
 using System.Diagnostics;
 using osu.Game.Beatmaps;
+using osu.Game.Extensions;
 using osu.Game.Online.API;
 using osu.Game.Online.Rooms;
 using osu.Game.Online.Solo;
@@ -31,7 +32,7 @@ namespace osu.Game.Screens.Play
             if (beatmapId <= 0)
                 return null;
 
-            if (!Ruleset.Value.IsLegacyRuleset)
+            if (!Ruleset.Value.IsLegacyRuleset())
                 return null;
 
             return new CreateSoloScoreRequest(beatmapId, rulesetId, Game.VersionHash);

osu.Game/Screens/Select/Leaderboards/BeatmapLeaderboard.cs

@@ -11,6 +11,7 @@ using osu.Framework.Bindables;
 using osu.Framework.Extensions;
 using osu.Game.Beatmaps;
 using osu.Game.Database;
+using osu.Game.Extensions;
 using osu.Game.Online.API;
 using osu.Game.Online.API.Requests;
 using osu.Game.Online.Leaderboards;
@@ -118,7 +119,7 @@ namespace osu.Game.Screens.Select.Leaderboards
                 return null;
             }
 
-            if (!fetchRuleset.IsLegacyRuleset)
+            if (!fetchRuleset.IsLegacyRuleset())
             {
                 SetErrorState(LeaderboardState.RulesetUnavailable);
                 return null;