Fixes bug in MessageBox scenario that is latent in v1

Terminal.Gui/Core/View.cs

@@ -2458,9 +2458,13 @@ namespace Terminal.Gui {
 				(var from, var to) = edges.First ();
 				if (from != superView?.GetTopSuperView (to, from)) {
 					if (!ReferenceEquals (from, to)) {
-						throw new InvalidOperationException ($"TopologicalSort (for Pos/Dim) cannot find {from} linked with {to}. Did you forget to add it to {superView}?");
+						if (ReferenceEquals (from.SuperView, to)) {
+							throw new InvalidOperationException ($"ComputedLayout for \"{superView}\": \"{to}\" references a SubView (\"{from}\").");
+						} else {
+							throw new InvalidOperationException ($"ComputedLayout for \"{superView}\": \"{from}\" linked with \"{to}\" was not found. Did you forget to add it to {superView}?");
+						}
 					} else {
-						throw new InvalidOperationException ("TopologicalSort encountered a recursive cycle in the relative Pos/Dim in the views of " + superView);
+						throw new InvalidOperationException ($"ComputedLayout for \"{superView}\": A recursive cycle was found in the relative Pos/Dim of the SubViews.");
 					}
 				}
 			}

UICatalog/Scenarios/MessageBoxes.cs

@@ -159,10 +159,37 @@ namespace UICatalog.Scenarios {
 			};
 			frame.Add (ckbWrapMessage);
 
+			frame.ForceValidatePosDim = true;
+
 			void Top_Loaded ()
 			{
-				frame.Height = Dim.Height (widthEdit) + Dim.Height (heightEdit) + Dim.Height (titleEdit) + Dim.Height (messageEdit)
-				+ Dim.Height (numButtonsEdit) + Dim.Height (defaultButtonEdit) + Dim.Height (styleRadioGroup) + 2 + Dim.Height (ckbEffect3D) + Dim.Height (ckbWrapMessage);
+				frame.Height =
+					widthEdit.Frame.Height +
+					heightEdit.Frame.Height +
+					titleEdit.Frame.Height +
+					messageEdit.Frame.Height +
+					numButtonsEdit.Frame.Height +
+					defaultButtonEdit.Frame.Height +
+					styleRadioGroup.Frame.Height +
+					2 +
+					ckbEffect3D.Frame.Height +
+					ckbWrapMessage.Frame.Height;
+
+				// BUGBUG: this only worked because the subviews are actually added
+				// to FrameView.ContentView, not FrameView itself. In v2 this breaks because FrameView
+				// does not have a ContentView.
+				// 
+				//Dim.Height (widthEdit) +
+				//Dim.Height (heightEdit);
+				//+
+				//Dim.Height (titleEdit) +
+				//Dim.Height (messageEdit) +
+				//Dim.Height (numButtonsEdit) +
+				//Dim.Height (defaultButtonEdit) +
+				//Dim.Height (styleRadioGroup) +
+				//2 +
+				//Dim.Height (ckbEffect3D) +
+				//Dim.Height (ckbWrapMessage);
 				Application.Top.Loaded -= Top_Loaded;
 			}
 			Application.Top.Loaded += Top_Loaded;

UnitTests/Core/LayoutTests.cs

@@ -47,6 +47,56 @@ namespace Terminal.Gui.CoreTests {
 			Assert.Throws<InvalidOperationException> (() => root.LayoutSubviews ());
 		}
 
+		[Fact]
+		public void LayoutSubviews_No_SuperView ()
+		{
+			var root = new View ();
+			var first = new View () { Id = "first", X = 1, Y = 2, Height = 3, Width = 4 };
+			root.Add (first);
+
+			var second = new View () { Id = "second" };
+			root.Add (second);
+
+			second.X = Pos.Right (first) + 1;
+
+			root.LayoutSubviews ();
+			
+			Assert.Equal (6, second.Frame.X);
+		}
+
+		[Fact]
+		public void LayoutSubviews_RootHas_SuperView ()
+		{
+			var top = new View ();
+			var root = new View ();
+			top.Add (root);
+
+			var first = new View () { Id = "first", X = 1, Y = 2, Height = 3, Width = 4 };
+			root.Add (first);
+
+			var second = new View () { Id = "second" };
+			root.Add (second);
+
+			second.X = Pos.Right (first) + 1;
+
+			root.LayoutSubviews ();
+
+			Assert.Equal (6, second.Frame.X);
+		}
+
+
+		[Fact]
+		public void LayoutSubviews_ViewThatRefsSuperView_Throws ()
+		{
+			var root = new View ();
+			var super = new View ();
+			root.Add (super);
+			var sub = new View ();
+			super.Add (sub);
+			super.Width = Dim.Width (sub);
+			Assert.Throws<InvalidOperationException> (() => root.LayoutSubviews ());
+		}
+
 		[Fact, AutoInitShutdown]
 		public void TrySetWidth_ForceValidatePosDim ()
 		{