Don't create undo history item for a paste that does nothing.

Author: SuuperW

src/BizHawk.Client.Common/movie/tasproj/TasMovie.Editing.cs

@@ -175,35 +175,26 @@ public void InsertInput(int frame, IEnumerable<IController> inputStates)
 
 		public void CopyOverInput(int frame, IEnumerable<IController> inputStates)
 		{
-			int firstChangedFrame = -1;
 			var states = inputStates.ToList();
 
 			bool endBatch = ChangeLog.BeginNewBatch($"Copy Over Input: {frame}", true);
 
 			if (Log.Count < states.Count + frame)
 			{
-				firstChangedFrame = Log.Count;
 				ExtendMovieForEdit(states.Count + frame - Log.Count);
 			}
 
 			ChangeLog.AddGeneralUndo(frame, frame + states.Count - 1, $"Copy Over Input: {frame}");
 			for (int i = 0; i < states.Count; i++)
 			{
-				var entry = Bk2LogEntryGenerator.GenerateLogEntry(states[i]);
-				if ((firstChangedFrame == -1 || firstChangedFrame > frame + i) && Log[frame + i] != entry)
-				{
-					firstChangedFrame = frame + i;
-				}
-
-				Log[frame + i] = entry;
+				Log[frame + i] = Bk2LogEntryGenerator.GenerateLogEntry(states[i]);
 			}
-			ChangeLog.SetGeneralRedo();
+			int firstChangedFrame = ChangeLog.SetGeneralRedo();
 
 			if (endBatch) ChangeLog.EndBatch();
 
 			if (firstChangedFrame != -1)
 			{
-				// TODO: Throw out the undo action if there are no changes.
 				InvalidateAfter(firstChangedFrame);
 			}
 		}

src/BizHawk.Client.Common/movie/tasproj/TasMovie.History.cs

@@ -41,7 +41,7 @@ public interface IMovieChangeLog
 		int MaxSteps { get; set; }
 
 		void AddGeneralUndo(int first, int last, string name = "");
-		void SetGeneralRedo();
+		int SetGeneralRedo();
 		void AddBoolToggle(int frame, string button, bool oldState, string name = "");
 		void AddAxisChange(int frame, string button, int oldState, int newState, string name = "");
 		void AddMarkerChange(TasMovieMarker newMarker, int oldPosition = -1, string oldMessage = "", string name = "");
@@ -263,13 +263,25 @@ public void AddGeneralUndo(int first, int last, string name = "")
 			}
 		}
 
-		public void SetGeneralRedo()
+		public int SetGeneralRedo()
 		{
 			if (IsRecording)
 			{
 				Debug.Assert(_lastGeneral == LatestBatch.Count - 1, "GeneralRedo should not see changes from other undo actions.");
-				((MovieAction) LatestBatch[_lastGeneral]).SetRedoLog(_movie);
+				int changed = ((MovieAction) LatestBatch[_lastGeneral]).SetRedoLog(_movie);
+				if (changed == -1)
+				{
+					LatestBatch.RemoveAt(_lastGeneral);
+					if (LatestBatch.Count == 0 && !_recordingBatch)
+					{
+						// Remove this undo item
+						_recordingBatch = true;
+						EndBatch();
+					}
+				}
+				return changed;
 			}
+			return -1;
 		}
 
 		public void AddBoolToggle(int frame, string button, bool oldState, string name = "")
@@ -387,14 +399,21 @@ public MovieAction(int firstFrame, int lastFrame, ITasMovie movie)
 			_bindMarkers = movie.BindMarkersToInput;
 		}
 
-		public void SetRedoLog(ITasMovie movie)
+		/// <returns>Returns the first frame that has changed, or -1 if no changes.</returns>
+		public int SetRedoLog(ITasMovie movie)
 		{
 			_redoLength = Math.Min(LastFrame + 1, movie.InputLogLength) - FirstFrame;
 			_newLog = new List<string>(_redoLength);
+			int changed = Math.Min(_redoLength, _undoLength);
 			for (int i = 0; i < _redoLength; i++)
 			{
-				_newLog.Add(movie.GetInputLogEntry(FirstFrame + i));
+				string newEntry = movie.GetInputLogEntry(FirstFrame + i);
+				_newLog.Add(newEntry);
+				if (i < changed && newEntry != _oldLog[i]) changed = i;
 			}
+
+			if (changed == _redoLength && changed == _undoLength) return -1;
+			else return changed + FirstFrame;
 		}
 
 		public void Undo(ITasMovie movie)