Fix "InvalidOperationException: Trying to build visual line from collapsed line" when the start of a folding section is hidden by a different element generator than the FoldingElementGenerator. (e.g. TruncateLongLines)

src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Editing/ImeSupport.cs

@@ -107,8 +107,6 @@ namespace ICSharpCode.AvalonEdit.Editing
 					currentContext = ImeNativeWrapper.ImmGetContext(defaultImeWnd);
 				}
 				previousContext = ImeNativeWrapper.ImmAssociateContext(hwndSource.Handle, currentContext);
-				Debug.Assert(hwndSource != null);
-				Debug.Assert(currentContext != null);
 				hwndSource.AddHook(WndProc);
 				// UpdateCompositionWindow() will be called by the caret becoming visible
 				

src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Folding/FoldingElementGenerator.cs

@@ -73,10 +73,19 @@ namespace ICSharpCode.AvalonEdit.Folding
 		/// <inheritdoc/>
 		public override int GetFirstInterestedOffset(int startOffset)
 		{
-			if (foldingManager != null)
+			if (foldingManager != null) {
+				foreach (FoldingSection fs in foldingManager.GetFoldingsContaining(startOffset)) {
+					// Test whether we're currently within a folded folding (that didn't just end).
+					// If so, create the fold marker immediately.
+					// This is necessary if the actual beginning of the fold marker got skipped due to another VisualElementGenerator.
+					if (fs.IsFolded && fs.EndOffset > startOffset) {
+						//return startOffset;
+					}
+				}
 				return foldingManager.GetNextFoldedFoldingStart(startOffset);
-			else
+			} else {
 				return -1;
+			}
 		}
 		
 		/// <inheritdoc/>
@@ -86,7 +95,7 @@ namespace ICSharpCode.AvalonEdit.Folding
 				return null;
 			int foldedUntil = -1;
 			FoldingSection foldingSection = null;
-			foreach (FoldingSection fs in foldingManager.GetFoldingsAt(offset)) {
+			foreach (FoldingSection fs in foldingManager.GetFoldingsContaining(offset)) {
 				if (fs.IsFolded) {
 					if (fs.EndOffset > foldedUntil) {
 						foldedUntil = fs.EndOffset;