Fix UndoStack.StartContinuedUndoGroup() if the previous undo group was empty.

src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit.Tests/Document/UndoStackTests.cs

@@ -0,0 +1,77 @@
+// Copyright (c) AlphaSierraPapa for the SharpDevelop Team (for details please see \doc\copyright.txt)
+// This code is distributed under the GNU LGPL (for details please see \doc\license.txt)
+
+using System;
+using NUnit.Framework;
+
+namespace ICSharpCode.AvalonEdit.Document
+{
+	public class UndoStackTests
+	{
+		[Test]
+		public void ContinueUndoGroup()
+		{
+			var doc = new TextDocument();
+			doc.Insert(0, "a");
+			doc.UndoStack.StartContinuedUndoGroup();
+			doc.Insert(1, "b");
+			doc.UndoStack.EndUndoGroup();
+			doc.UndoStack.Undo();
+			Assert.AreEqual("", doc.Text);
+		}
+		
+		[Test]
+		public void ContinueEmptyUndoGroup()
+		{
+			var doc = new TextDocument();
+			doc.Insert(0, "a");
+			doc.UndoStack.StartUndoGroup();
+			doc.UndoStack.EndUndoGroup();
+			doc.UndoStack.StartContinuedUndoGroup();
+			doc.Insert(1, "b");
+			doc.UndoStack.EndUndoGroup();
+			doc.UndoStack.Undo();
+			Assert.AreEqual("a", doc.Text);
+		}
+		
+		[Test]
+		public void ContinueEmptyUndoGroup_WithOptionalEntries()
+		{
+			var doc = new TextDocument();
+			doc.Insert(0, "a");
+			doc.UndoStack.StartUndoGroup();
+			doc.UndoStack.PushOptional(new StubUndoableAction());
+			doc.UndoStack.EndUndoGroup();
+			doc.UndoStack.StartContinuedUndoGroup();
+			doc.Insert(1, "b");
+			doc.UndoStack.EndUndoGroup();
+			doc.UndoStack.Undo();
+			Assert.AreEqual("a", doc.Text);
+		}
+		
+		[Test]
+		public void EmptyContinuationGroup()
+		{
+			var doc = new TextDocument();
+			doc.Insert(0, "a");
+			doc.UndoStack.StartContinuedUndoGroup();
+			doc.UndoStack.EndUndoGroup();
+			doc.UndoStack.StartContinuedUndoGroup();
+			doc.Insert(1, "b");
+			doc.UndoStack.EndUndoGroup();
+			doc.UndoStack.Undo();
+			Assert.AreEqual("", doc.Text);
+		}
+		
+		class StubUndoableAction : IUndoableOperation
+		{
+			public void Undo()
+			{
+			}
+			
+			public void Redo()
+			{
+			}
+		}
+	}
+}

src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit.Tests/ICSharpCode.AvalonEdit.Tests.csproj

@@ -83,6 +83,7 @@
     <Compile Include="Document\TextAnchorTest.cs" />
     <Compile Include="Document\TextSegmentTreeTest.cs" />
     <Compile Include="Document\TextUtilitiesTests.cs" />
+    <Compile Include="Document\UndoStackTests.cs" />
     <Compile Include="Editing\ChangeDocumentTests.cs" />
     <Compile Include="Editing\TextSegmentReadOnlySectionTests.cs" />
     <Compile Include="Highlighting\HighlightedLineMergeTests.cs" />

src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Document/UndoStack.cs

@@ -214,11 +214,13 @@ namespace ICSharpCode.AvalonEdit.Document
 			//Util.LoggingService.Debug("Close undo group (new depth=" + undoGroupDepth + ")");
 			if (undoGroupDepth == 0) {
 				Debug.Assert(state == StateListen || actionCountInUndoGroup == 0);
+				allowContinue = true;
 				if (actionCountInUndoGroup == optionalActionCount) {
 					// only optional actions: don't store them
 					for (int i = 0; i < optionalActionCount; i++) {
 						undostack.PopBack();
 					}
+					allowContinue = false;
 				} else if (actionCountInUndoGroup > 1) {
 					// combine all actions within the group into a single grouped action
 					undostack.PushBack(new UndoOperationGroup(undostack, actionCountInUndoGroup));
@@ -226,7 +228,6 @@ namespace ICSharpCode.AvalonEdit.Document
 				}
 				//if (state == StateListen) {
 				EnforceSizeLimit();
-				allowContinue = true;
 				RecalcIsOriginalFile(); // can raise event
 				//}
 			}