Handle screen buffer scrolling correctly for inline dynamic help (#2951)

Author: daxian-dbw

PSReadLine/DynamicHelp.cs

@@ -233,13 +233,14 @@ private class MultilineDisplayBlock : DisplayBlockBase
         {
             internal Collection<string> ItemsToDisplay;
 
-            private int multilineItems = 0;
+            // Keep track of the number of extra physical lines due to multi-line text.
+            private int extraPhysicalLines = 0;
 
             public void DrawMultilineBlock()
             {
                 IConsole console = Singleton._console;
 
-                multilineItems = 0;
+                extraPhysicalLines = 0;
 
                 SaveCursor();
                 MoveCursorToStartDrawingPosition(console);
@@ -251,16 +252,23 @@ public void DrawMultilineBlock()
                 {
                     var itemLength = LengthInBufferCells(items[index]);
 
+                    int extra = 0;
                     if (itemLength > bufferWidth)
                     {
-                        multilineItems += itemLength / bufferWidth;
-
+                        extra = itemLength / bufferWidth;
                         if (itemLength % bufferWidth == 0)
                         {
-                            multilineItems--;
+                            extra--;
                         }
                     }
 
+                    if (extra > 0)
+                    {
+                        // Extra physical lines may cause buffer to scroll up.
+                        AdjustForPossibleScroll(extra);
+                        extraPhysicalLines += extra;
+                    }
+
                     console.Write(items[index]);
 
                     // Explicit newline so consoles see each row as distinct lines, but skip the
@@ -277,7 +285,7 @@ public void DrawMultilineBlock()
 
             public void Clear()
             {
-                _singleton.WriteBlankLines(Top, ItemsToDisplay.Count + multilineItems);
+                _singleton.WriteBlankLines(Top, ItemsToDisplay.Count + extraPhysicalLines);
             }
         }
     }