Move the CreateConvertibleReplayFrame() into the base ruleset class for avoid api breaking change in the customized ruleset.

osu.Game.Rulesets.Catch/CatchRuleset.cs

@@ -188,7 +188,7 @@ namespace osu.Game.Rulesets.Catch
 
         public int LegacyID => 2;
 
-        public IConvertibleReplayFrame CreateConvertibleReplayFrame() => new CatchReplayFrame();
+        public override IConvertibleReplayFrame CreateConvertibleReplayFrame() => new CatchReplayFrame();
 
         public override HitObjectComposer CreateHitObjectComposer() => new CatchHitObjectComposer(this);
 

osu.Game.Rulesets.Mania/ManiaRuleset.cs

@@ -281,7 +281,7 @@ namespace osu.Game.Rulesets.Mania
 
         public int LegacyID => 3;
 
-        public IConvertibleReplayFrame CreateConvertibleReplayFrame() => new ManiaReplayFrame();
+        public override IConvertibleReplayFrame CreateConvertibleReplayFrame() => new ManiaReplayFrame();
 
         public override IRulesetConfigManager CreateConfig(SettingsStore? settings) => new ManiaRulesetConfigManager(settings, RulesetInfo);
 

osu.Game.Rulesets.Osu/OsuRuleset.cs

@@ -235,7 +235,7 @@ namespace osu.Game.Rulesets.Osu
 
         public int LegacyID => 0;
 
-        public IConvertibleReplayFrame CreateConvertibleReplayFrame() => new OsuReplayFrame();
+        public override IConvertibleReplayFrame CreateConvertibleReplayFrame() => new OsuReplayFrame();
 
         public override IRulesetConfigManager CreateConfig(SettingsStore? settings) => new OsuRulesetConfigManager(settings, RulesetInfo);
 

osu.Game.Rulesets.Taiko/TaikoRuleset.cs

@@ -178,7 +178,7 @@ namespace osu.Game.Rulesets.Taiko
 
         public int LegacyID => 1;
 
-        public IConvertibleReplayFrame CreateConvertibleReplayFrame() => new TaikoReplayFrame();
+        public override IConvertibleReplayFrame CreateConvertibleReplayFrame() => new TaikoReplayFrame();
 
         protected override IEnumerable<HitResult> GetValidHitResults()
         {

osu.Game/Rulesets/ILegacyRuleset.cs

@@ -1,8 +1,6 @@
 // Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
 // See the LICENCE file in the repository root for full licence text.
 
-using osu.Game.Rulesets.Replays.Types;
-
 namespace osu.Game.Rulesets
 {
     public interface ILegacyRuleset
@@ -13,12 +11,5 @@ namespace osu.Game.Rulesets
         /// Identifies the server-side ID of a legacy ruleset.
         /// </summary>
         int LegacyID { get; }
-
-        /// <summary>
-        /// For rulesets which support legacy (osu-stable) replay conversion, this method will create an empty replay frame
-        /// for conversion use.
-        /// </summary>
-        /// <returns>An empty frame for the current ruleset, or null if unsupported.</returns>
-        IConvertibleReplayFrame CreateConvertibleReplayFrame();
     }
 }

osu.Game/Rulesets/Ruleset.cs

@@ -23,6 +23,7 @@ using osu.Game.Rulesets.Difficulty;
 using osu.Game.Rulesets.Edit;
 using osu.Game.Rulesets.Filter;
 using osu.Game.Rulesets.Mods;
+using osu.Game.Rulesets.Replays.Types;
 using osu.Game.Rulesets.Scoring;
 using osu.Game.Rulesets.UI;
 using osu.Game.Scoring;
@@ -302,6 +303,13 @@ namespace osu.Game.Rulesets
         /// <returns>A descriptive name of the variant.</returns>
         public virtual LocalisableString GetVariantName(int variant) => string.Empty;
 
+        /// <summary>
+        /// For rulesets which support legacy (osu-stable) replay conversion, this method will create an empty replay frame
+        /// for conversion use.
+        /// </summary>
+        /// <returns>An empty frame for the current ruleset, or null if unsupported.</returns>
+        public virtual IConvertibleReplayFrame? CreateConvertibleReplayFrame() => null;
+
         /// <summary>
         /// Creates the statistics for a <see cref="ScoreInfo"/> to be displayed in the results screen.
         /// </summary>

osu.Game/Scoring/Legacy/LegacyScoreDecoder.cs

@@ -282,7 +282,7 @@ namespace osu.Game.Scoring.Legacy
 
         private ReplayFrame convertFrame(LegacyReplayFrame currentFrame, ReplayFrame lastFrame)
         {
-            var convertible = (currentRuleset as ILegacyRuleset)?.CreateConvertibleReplayFrame();
+            var convertible = currentRuleset.CreateConvertibleReplayFrame();
             if (convertible == null)
                 throw new InvalidOperationException($"Legacy replay cannot be converted for the ruleset: {currentRuleset.Description}");
 

osu.Game/Screens/Play/SpectatorPlayer.cs

@@ -11,7 +11,6 @@ using osu.Game.Beatmaps;
 using osu.Game.Graphics;
 using osu.Game.Graphics.Sprites;
 using osu.Game.Online.Spectator;
-using osu.Game.Rulesets;
 using osu.Game.Rulesets.Replays;
 using osu.Game.Rulesets.Replays.Types;
 using osu.Game.Scoring;
@@ -81,14 +80,12 @@ namespace osu.Game.Screens.Play
             if (!this.IsCurrentScreen())
                 return;
 
-            var legacyRuleset = GameplayState.Ruleset as ILegacyRuleset;
-            Debug.Assert(legacyRuleset != null);
-
             bool isFirstBundle = score.Replay.Frames.Count == 0;
 
             foreach (var frame in bundle.Frames)
             {
-                IConvertibleReplayFrame convertibleFrame = legacyRuleset.CreateConvertibleReplayFrame();
+                IConvertibleReplayFrame convertibleFrame = GameplayState.Ruleset.CreateConvertibleReplayFrame();
+                Debug.Assert(convertibleFrame != null);
                 convertibleFrame.FromLegacy(frame, GameplayState.Beatmap);
 
                 var convertedFrame = (ReplayFrame)convertibleFrame;