Ensures that the isButtonShift flag is disabled in all situations. (#1945)

* Ensures that the isButtonShift flag is disabled in all situations.

* Improving this unit test.

Terminal.Gui/Views/TextView.cs

@@ -3871,6 +3871,7 @@ namespace Terminal.Gui {
 		{
 			shiftSelecting = false;
 			selecting = false;
+			isButtonShift = false;
 		}
 
 		void ClearSelectedRegion ()
@@ -4185,8 +4186,6 @@ namespace Terminal.Gui {
 			if (ev.Flags == MouseFlags.Button1Clicked) {
 				if (shiftSelecting && !isButtonShift) {
 					StopSelecting ();
-				} else if (!shiftSelecting && isButtonShift) {
-					isButtonShift = false;
 				}
 				ProcessMouseClick (ev, out _);
 				PositionCursor ();

UnitTests/TextViewTests.cs

@@ -1323,20 +1323,26 @@ namespace Terminal.Gui.Views {
 			Assert.Equal ("TAB to jump between text fields.", _textView.Text);
 			_textView.SelectionStartColumn = 0;
 			_textView.SelectionStartRow = 0;
+			Assert.Equal (new Point (24, 0), _textView.CursorPosition);
 			Assert.True (_textView.Selecting);
 			_textView.Selecting = false;
 			_textView.ProcessKey (new KeyEvent (Key.Y | Key.CtrlMask, new KeyModifiers ())); // Paste
+			Assert.Equal (new Point (28, 0), _textView.CursorPosition);
+			Assert.False (_textView.Selecting);
 			Assert.Equal ("TAB to jump between texttext fields.", _textView.Text);
 			_textView.SelectionStartColumn = 24;
 			_textView.SelectionStartRow = 0;
 			_textView.ProcessKey (new KeyEvent (Key.W | Key.CtrlMask, new KeyModifiers ())); // Cut
+			Assert.Equal (new Point (24, 0), _textView.CursorPosition);
+			Assert.False (_textView.Selecting);
 			Assert.Equal ("", _textView.SelectedText);
 			Assert.Equal ("TAB to jump between text fields.", _textView.Text);
 			_textView.SelectionStartColumn = 0;
 			_textView.SelectionStartRow = 0;
-			Assert.True (_textView.Selecting);
 			_textView.Selecting = false;
 			_textView.ProcessKey (new KeyEvent (Key.Y | Key.CtrlMask, new KeyModifiers ())); // Paste
+			Assert.Equal (new Point (28, 0), _textView.CursorPosition);
+			Assert.False (_textView.Selecting);
 			Assert.Equal ("TAB to jump between texttext fields.", _textView.Text);
 		}
 
@@ -5873,5 +5879,60 @@ line.
 			tv.CursorPosition = new Point (tv.LeftColumn, tv.TopRow);
 			Assert.Equal (new Point (0, 50), tv.CursorPosition);
 		}
+
+		[Fact]
+		[InitShutdown]
+		public void Mouse_Button_Shift_Preserves_Selection ()
+		{
+			Assert.Equal ("TAB to jump between text fields.", _textView.Text);
+			Assert.True (_textView.MouseEvent (new MouseEvent () { X = 12, Y = 0, Flags = MouseFlags.Button1Pressed | MouseFlags.ButtonShift }));
+			Assert.Equal (0, _textView.SelectionStartColumn);
+			Assert.Equal (0, _textView.SelectionStartRow);
+			Assert.Equal (new Point (12, 0), _textView.CursorPosition);
+			Assert.True (_textView.Selecting);
+			Assert.Equal ("TAB to jump ", _textView.SelectedText);
+
+			Assert.True (_textView.MouseEvent (new MouseEvent () { X = 12, Y = 0, Flags = MouseFlags.Button1Clicked }));
+			Assert.Equal (0, _textView.SelectionStartRow);
+			Assert.Equal (0, _textView.SelectionStartRow);
+			Assert.Equal (new Point (12, 0), _textView.CursorPosition);
+			Assert.True (_textView.Selecting);
+			Assert.Equal ("TAB to jump ", _textView.SelectedText);
+
+			Assert.True (_textView.MouseEvent (new MouseEvent () { X = 19, Y = 0, Flags = MouseFlags.Button1Pressed | MouseFlags.ButtonShift }));
+			Assert.Equal (0, _textView.SelectionStartRow);
+			Assert.Equal (0, _textView.SelectionStartRow);
+			Assert.Equal (new Point (19, 0), _textView.CursorPosition);
+			Assert.True (_textView.Selecting);
+			Assert.Equal ("TAB to jump between", _textView.SelectedText);
+
+			Assert.True (_textView.MouseEvent (new MouseEvent () { X = 19, Y = 0, Flags = MouseFlags.Button1Clicked }));
+			Assert.Equal (0, _textView.SelectionStartRow);
+			Assert.Equal (0, _textView.SelectionStartRow);
+			Assert.Equal (new Point (19, 0), _textView.CursorPosition);
+			Assert.True (_textView.Selecting);
+			Assert.Equal ("TAB to jump between", _textView.SelectedText);
+
+			Assert.True (_textView.MouseEvent (new MouseEvent () { X = 24, Y = 0, Flags = MouseFlags.Button1Pressed | MouseFlags.ButtonShift }));
+			Assert.Equal (0, _textView.SelectionStartRow);
+			Assert.Equal (0, _textView.SelectionStartRow);
+			Assert.Equal (new Point (24, 0), _textView.CursorPosition);
+			Assert.True (_textView.Selecting);
+			Assert.Equal ("TAB to jump between text", _textView.SelectedText);
+
+			Assert.True (_textView.MouseEvent (new MouseEvent () { X = 24, Y = 0, Flags = MouseFlags.Button1Clicked }));
+			Assert.Equal (0, _textView.SelectionStartRow);
+			Assert.Equal (0, _textView.SelectionStartRow);
+			Assert.Equal (new Point (24, 0), _textView.CursorPosition);
+			Assert.True (_textView.Selecting);
+			Assert.Equal ("TAB to jump between text", _textView.SelectedText);
+
+			Assert.True (_textView.MouseEvent (new MouseEvent () { X = 24, Y = 0, Flags = MouseFlags.Button1Pressed }));
+			Assert.Equal (0, _textView.SelectionStartRow);
+			Assert.Equal (0, _textView.SelectionStartRow);
+			Assert.Equal (new Point (24, 0), _textView.CursorPosition);
+			Assert.True (_textView.Selecting);
+			Assert.Equal ("", _textView.SelectedText);
+		}
 	}
 }