Handle screen buffer scrolling correctly for inline dynamic help (PowerShell#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);
  }
  }
  }