Fix 2 menu completion issues that happen when we need to scroll screen buffer (#2949)

Author: daxian-dbw

PSReadLine/Completion.cs

@@ -445,15 +445,8 @@ public void DrawMenu(Menu previousMenu, bool menuSelect)
                     SaveCursor();
                 }
 
-                // Move cursor to the start of the first line after our input.
-                var bufferEndPoint = Singleton.ConvertOffsetToPoint(Singleton._buffer.Length);
-                console.SetCursorPosition(bufferEndPoint.X, bufferEndPoint.Y);
-                // Top must be initialized before calling AdjustForPossibleScroll, otherwise
-                // on the last line of the buffer, the scroll operation causes Top to point
-                // past the buffer, which in turn causes the menu to be printed twice.
-                this.Top = bufferEndPoint.Y + 1;
-                AdjustForPossibleScroll(1);
-                MoveCursorDown(1);
+                PreviousTop = Top;
+                MoveCursorToStartDrawingPosition(console);
 
                 var bufferWidth = console.BufferWidth;
                 var columnWidth = this.ColumnWidth;
@@ -514,7 +507,7 @@ public void DrawMenu(Menu previousMenu, bool menuSelect)
                 }
 
                 // if the menu has moved, we need to clear the lines under it
-                if (bufferEndPoint.Y < PreviousTop)
+                if (Top < PreviousTop)
                 {
                     // In either of the following two cases, we will need to move the cursor to the next line:
                     //  - if extra rows from previous menu were cleared, then we know the current line was erased
@@ -528,11 +521,9 @@ public void DrawMenu(Menu previousMenu, bool menuSelect)
                         MoveCursorDown(1);
                     }
 
-                    Singleton.WriteBlankLines(PreviousTop - bufferEndPoint.Y);
+                    Singleton.WriteBlankLines(PreviousTop - Top);
                 }
 
-                PreviousTop = bufferEndPoint.Y;
-
                 if (menuSelect)
                 {
                     RestoreCursor();
@@ -797,7 +788,7 @@ private void PossibleCompletionsImpl(CommandCompletion completions, bool menuSel
             }
             else
             {
-                menu.DrawMenu(null, menuSelect:false);
+                menu.DrawMenu(null, menuSelect: false);
                 InvokePrompt(key: null, arg: _console.CursorTop);
             }
         }
@@ -879,7 +870,6 @@ private void MenuCompleteImpl(Menu menu, CommandCompletion completions)
 
                         if (topAdjustment != 0)
                         {
-                            menu.Top += topAdjustment;
                             menu.DrawMenu(null, menuSelect: true);
                         }
                         if (topAdjustment > 0)
@@ -963,7 +953,7 @@ private void MenuCompleteImpl(Menu menu, CommandCompletion completions)
                     {
                         var newMenu = menuStack.Pop();
 
-                        newMenu.DrawMenu(menu, menuSelect:true);
+                        newMenu.DrawMenu(menu, menuSelect: true);
                         previousSelection = -1;
 
                         menu = newMenu;
@@ -1025,7 +1015,7 @@ private void MenuCompleteImpl(Menu menu, CommandCompletion completions)
                         {
                             var newMenu = CreateCompletionMenu(newMatches);
 
-                            newMenu.DrawMenu(menu, menuSelect:true);
+                            newMenu.DrawMenu(menu, menuSelect: true);
                             previousSelection = -1;
 
                             // Remember the current menu for when we see Backspace.

PSReadLine/DisplayBlockBase.cs

@@ -23,6 +23,16 @@ protected void MoveCursorDown(int cnt)
                 }
             }
 
+            protected void AdjustForActualScroll(int scrollCnt)
+            {
+                if (scrollCnt > 0)
+                {
+                    Top -= scrollCnt;
+                    _singleton._initialY -= scrollCnt;
+                    _savedCursorTop -= scrollCnt;
+                }
+            }
+
             protected void AdjustForPossibleScroll(int cnt)
             {
                 IConsole console = Singleton._console;
@@ -35,6 +45,34 @@ protected void AdjustForPossibleScroll(int cnt)
                 }
             }
 
+            protected void MoveCursorToStartDrawingPosition(IConsole console)
+            {
+                // Calculate the coord to place the cursor at the end of current input.
+                Point bufferEndPoint = Singleton.ConvertOffsetToPoint(Singleton._buffer.Length);
+                // Top must be initialized before any possible adjustion by 'AdjustForPossibleScroll' or 'AdjustForActualScroll',
+                // otherwise its value would be corrupted and cause rendering issue.
+                Top = bufferEndPoint.Y + 1;
+
+                if (bufferEndPoint.Y == console.BufferHeight)
+                {
+                    // The input happens to end at the very last cell of the current buffer, so 'bufferEndPoint' is pointing to
+                    // the first cell at one line below the current buffer, and thus we need to scroll up the buffer.
+                    console.SetCursorPosition(console.BufferWidth - 1, console.BufferHeight - 1);
+                    // We scroll the buffer by 2 lines here, so the cursor is placed at the start of the first line after 'bufferEndPoint'.
+                    MoveCursorDown(2);
+                    bufferEndPoint.Y -= 2;
+                    AdjustForActualScroll(2);
+                }
+                else
+                {
+                    // Move the cursor to the end of our input.
+                    console.SetCursorPosition(bufferEndPoint.X, bufferEndPoint.Y);
+                    // Move cursor to the start of the first line after our input (after 'bufferEndPoint').
+                    AdjustForPossibleScroll(1);
+                    MoveCursorDown(1);
+                }
+            }
+
             private int _savedCursorLeft;
             private int _savedCursorTop;
 

PSReadLine/DynamicHelp.cs

@@ -241,21 +241,11 @@ public void DrawMultilineBlock()
 
                 multilineItems = 0;
 
-                this.SaveCursor();
-
-                // Move cursor to the start of the first line after our input.
-                var bufferEndPoint = Singleton.ConvertOffsetToPoint(Singleton._buffer.Length);
-                console.SetCursorPosition(bufferEndPoint.X, bufferEndPoint.Y);
-                // Top must be initialized before calling AdjustForPossibleScroll, otherwise
-                // on the last line of the buffer, the scroll operation causes Top to point
-                // past the buffer, which in turn causes the menu to be printed twice.
-                this.Top = bufferEndPoint.Y + 1;
-                AdjustForPossibleScroll(1);
-                MoveCursorDown(1);
+                SaveCursor();
+                MoveCursorToStartDrawingPosition(console);
 
                 var bufferWidth = console.BufferWidth;
-
-                var items = this.ItemsToDisplay;
+                var items = ItemsToDisplay;
 
                 for (var index = 0; index < items.Count; index++)
                 {
@@ -282,7 +272,7 @@ public void DrawMultilineBlock()
                     }
                 }
 
-                this.RestoreCursor();
+                RestoreCursor();
             }
 
             public void Clear()