Fixes #1380. Setting AllowsTab in TextView keeps Multiline.

Terminal.Gui/Views/TextView.cs

@@ -206,7 +206,7 @@ namespace Terminal.Gui {
 			last = last < lines.Count ? last : lines.Count;
 			for (int i = first; i < last; i++) {
 				var line = GetLine (i);
-				var tabSum = line.Sum (r => r == '\t' ? tabWidth - 1 : 0);
+				var tabSum = line.Sum (r => r == '\t' ? Math.Max (tabWidth - 1, 0) : 0);
 				var l = line.Count + tabSum;
 				if (l > maxLength) {
 					maxLength = l;
@@ -236,7 +236,7 @@ namespace Terminal.Gui {
 			for (int i = start; i < t.Count; i++) {
 				var r = t [i];
 				size += Rune.ColumnWidth (r);
-				if (r == '\t' && tabWidth > 0) {
+				if (r == '\t') {
 					size += tabWidth + 1;
 				}
 				if (i == pX || (size > pX)) {
@@ -261,7 +261,7 @@ namespace Terminal.Gui {
 				var rune = t [i];
 				size += Rune.ColumnWidth (rune);
 				len += Rune.RuneLen (rune);
-				if (rune == '\t' && tabWidth > 0) {
+				if (rune == '\t') {
 					size += tabWidth + 1;
 					len += tabWidth - 1;
 				}
@@ -276,7 +276,7 @@ namespace Terminal.Gui {
 			{
 				s = Rune.ColumnWidth (r);
 				l = Rune.RuneLen (r);
-				if (r == '\t' && tWidth > 0) {
+				if (r == '\t') {
 					s += tWidth + 1;
 					l += tWidth - 1;
 				}
@@ -1132,6 +1132,7 @@ namespace Terminal.Gui {
 					Multiline = false;
 					AllowsTab = false;
 				}
+				SetNeedsDisplay ();
 			}
 		}
 
@@ -1149,12 +1150,10 @@ namespace Terminal.Gui {
 				if (allowsTab && !multiline) {
 					Multiline = true;
 				}
-				if (!allowsTab && multiline) {
-					Multiline = false;
-				}
 				if (!allowsTab && tabWidth > 0) {
 					tabWidth = 0;
 				}
+				SetNeedsDisplay ();
 			}
 		}
 
@@ -1165,12 +1164,10 @@ namespace Terminal.Gui {
 			get => tabWidth;
 			set {
 				tabWidth = Math.Max (value, 0);
-				if (tabWidth == 0 && AllowsTab) {
-					AllowsTab = false;
-				}
 				if (tabWidth > 0 && !AllowsTab) {
 					AllowsTab = true;
 				}
+				SetNeedsDisplay ();
 			}
 		}
 
@@ -1306,7 +1303,7 @@ namespace Terminal.Gui {
 					if (idx >= currentColumn)
 						break;
 					var cols = Rune.ColumnWidth (line [idx]);
-					if (line [idx] == '\t' && TabWidth > 0) {
+					if (line [idx] == '\t') {
 						cols += TabWidth + 1;
 					}
 					TextModel.SetCol (ref col, Frame.Width, cols);
@@ -1701,7 +1698,7 @@ namespace Terminal.Gui {
 						ColorNormal (line, idxCol);
 					}
 
-					if (rune == '\t' && TabWidth > 0) {
+					if (rune == '\t') {
 						cols += TabWidth + 1;
 						if (col + cols > right) {
 							cols = right - col;

UICatalog/Scenarios/Editor.cs

@@ -68,7 +68,10 @@ namespace UICatalog {
 					new MenuItem ("  B_ox Fix", "", () => SetCursor(CursorVisibility.BoxFix)),
 					new MenuItem ("  U_nderline Fix","", () => SetCursor(CursorVisibility.UnderlineFix))
 				}),
-				new MenuBarItem ("Forma_t", CreateWrapChecked ())
+				new MenuBarItem ("Forma_t", new MenuItem [] {
+					CreateWrapChecked (),
+					CreateAllowsTabChecked ()
+				})
 			});
 			Top.Add (menu);
 
@@ -423,10 +426,11 @@ namespace UICatalog {
 			return new MenuItem [] { item };
 		}
 
-		private MenuItem [] CreateWrapChecked ()
+		private MenuItem CreateWrapChecked ()
 		{
-			var item = new MenuItem ();
-			item.Title = "Word Wrap";
+			var item = new MenuItem {
+				Title = "Word Wrap"
+			};
 			item.CheckType |= MenuItemCheckStyle.Checked;
 			item.Checked = false;
 			item.Action += () => {
@@ -441,7 +445,21 @@ namespace UICatalog {
 				}
 			};
 
-			return new MenuItem [] { item };
+			return item;
+		}
+
+		private MenuItem CreateAllowsTabChecked ()
+		{
+			var item = new MenuItem {
+				Title = "Allows Tab"
+			};
+			item.CheckType |= MenuItemCheckStyle.Checked;
+			item.Checked = true;
+			item.Action += () => {
+				_textView.AllowsTab = item.Checked = !item.Checked;
+			};
+
+			return item;
 		}
 
 		private void CreateFindReplace (bool isFind = true)

UnitTests/TextViewTests.cs

@@ -1418,7 +1418,7 @@ namespace Terminal.Gui.Views {
 
 		[Fact]
 		[InitShutdown]
-		public void TabWidth_Setting_To_Zero_Changes_AllowsTab_To_False_If_True ()
+		public void TabWidth_Setting_To_Zero_Keeps_AllowsTab ()
 		{
 			Assert.Equal (4, _textView.TabWidth);
 			Assert.True (_textView.AllowsTab);
@@ -1426,11 +1426,11 @@ namespace Terminal.Gui.Views {
 			Assert.True (_textView.Multiline);
 			_textView.TabWidth = -1;
 			Assert.Equal (0, _textView.TabWidth);
-			Assert.False (_textView.AllowsTab);
-			Assert.False (_textView.AllowsReturn);
-			Assert.False (_textView.Multiline);
+			Assert.True (_textView.AllowsTab);
+			Assert.True (_textView.AllowsReturn);
+			Assert.True (_textView.Multiline);
 			_textView.ProcessKey (new KeyEvent (Key.Tab, new KeyModifiers ()));
-			Assert.Equal ("TAB to jump between text fields.", _textView.Text);
+			Assert.Equal ("\tTAB to jump between text fields.", _textView.Text);
 			_textView.ProcessKey (new KeyEvent (Key.BackTab, new KeyModifiers ()));
 			Assert.Equal ("TAB to jump between text fields.", _textView.Text);
 		}
@@ -1441,9 +1441,9 @@ namespace Terminal.Gui.Views {
 		{
 			_textView.TabWidth = 0;
 			Assert.Equal (0, _textView.TabWidth);
-			Assert.False (_textView.AllowsTab);
-			Assert.False (_textView.AllowsReturn);
-			Assert.False (_textView.Multiline);
+			Assert.True (_textView.AllowsTab);
+			Assert.True (_textView.AllowsReturn);
+			Assert.True (_textView.Multiline);
 			_textView.AllowsTab = true;
 			Assert.True (_textView.AllowsTab);
 			Assert.Equal (4, _textView.TabWidth);
@@ -1761,6 +1761,20 @@ namespace Terminal.Gui.Views {
 			Application.Run ();
 		}
 
+		[Fact]
+		public void TextView_MultiLine_But_Without_Tabs ()
+		{
+			var view = new TextView ();
+
+			// the default for TextView
+			Assert.True (view.Multiline);
+
+			view.AllowsTab = false;
+			Assert.False (view.AllowsTab);
+
+			Assert.True (view.Multiline);
+		}
+
 		private int GetLeftCol (int start)
 		{
 			var lines = _textView.Text.Split (Environment.NewLine);