From 570e7a979c07547d3b5304f6b822e52823099dbc Mon Sep 17 00:00:00 2001
From: Steven Kirk <grokys@users.noreply.github.com>
Date: Mon, 8 May 2023 13:15:58 +0200
Subject: [PATCH 1/2] Added failing test for #11272.

---
 .../VirtualizingStackPanelTests.cs            | 43 ++++++++++++++++---
 1 file changed, 37 insertions(+), 6 deletions(-)

diff --git a/tests/Avalonia.Controls.UnitTests/VirtualizingStackPanelTests.cs b/tests/Avalonia.Controls.UnitTests/VirtualizingStackPanelTests.cs
index 61c21f46f4..951ca4e2c8 100644
--- a/tests/Avalonia.Controls.UnitTests/VirtualizingStackPanelTests.cs
+++ b/tests/Avalonia.Controls.UnitTests/VirtualizingStackPanelTests.cs
@@ -635,6 +635,22 @@ namespace Avalonia.Controls.UnitTests
             }
         }
 
+        [Fact]
+        public void Does_Not_Throw_When_Estimating_Viewport_With_Ancestor_Margin()
+        {
+            // Issue #11272
+            using var app = App();
+            var (_, _, itemsControl) = CreateUnrootedTarget();
+            var container = new Decorator { Margin = new Thickness(100) };
+            var root = new TestRoot(true, container);
+            
+            root.LayoutManager.ExecuteInitialLayoutPass();
+
+            container.Child = itemsControl;
+
+            root.LayoutManager.ExecuteLayoutPass();
+        }
+
         private static IReadOnlyList<int> GetRealizedIndexes(VirtualizingStackPanel target, ItemsControl itemsControl)
         {
             return target.GetRealizedElements()
@@ -681,6 +697,18 @@ namespace Avalonia.Controls.UnitTests
             IEnumerable<object>? items = null,
             Optional<IDataTemplate?> itemTemplate = default,
             IEnumerable<Style>? styles = null)
+        {
+            var (target, scroll, itemsControl) = CreateUnrootedTarget(items, itemTemplate);
+            var root = CreateRoot(itemsControl, styles);
+
+            root.LayoutManager.ExecuteInitialLayoutPass();
+
+            return (target, scroll, itemsControl);
+        }
+
+        private static (VirtualizingStackPanel, ScrollViewer, ItemsControl) CreateUnrootedTarget(
+            IEnumerable<object>? items = null,
+            Optional<IDataTemplate?> itemTemplate = default)
         {
             var target = new VirtualizingStackPanel();
 
@@ -691,8 +719,8 @@ namespace Avalonia.Controls.UnitTests
                 [~ItemsPresenter.ItemsPanelProperty] = new TemplateBinding(ItemsPresenter.ItemsPanelProperty),
             };
 
-            var scroll = new ScrollViewer 
-            { 
+            var scroll = new ScrollViewer
+            {
                 Name = "PART_ScrollViewer",
                 Content = presenter,
                 Template = ScrollViewerTemplate(),
@@ -706,15 +734,18 @@ namespace Avalonia.Controls.UnitTests
                 ItemTemplate = itemTemplate.GetValueOrDefault(DefaultItemTemplate()),
             };
 
-            var root = new TestRoot(true, itemsControl);
+            return (target, scroll, itemsControl);
+        }
+
+        private static TestRoot CreateRoot(Control? child, IEnumerable<Style>? styles = null)
+        {
+            var root = new TestRoot(true, child);
             root.ClientSize = new(100, 100);
 
             if (styles is not null)
                 root.Styles.AddRange(styles);
 
-            root.LayoutManager.ExecuteInitialLayoutPass();
-
-            return (target, scroll, itemsControl);
+            return root;
         }
 
         private static IDataTemplate DefaultItemTemplate()

From 2f50504ff3991380701b68e47fc4f2389279e1a7 Mon Sep 17 00:00:00 2001
From: Steven Kirk <grokys@users.noreply.github.com>
Date: Mon, 8 May 2023 13:17:45 +0200
Subject: [PATCH 2/2] Don't estimate negative top/left for viewport.

Fixes #11272.
---
 src/Avalonia.Controls/VirtualizingStackPanel.cs | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/src/Avalonia.Controls/VirtualizingStackPanel.cs b/src/Avalonia.Controls/VirtualizingStackPanel.cs
index ddeb42e560..7ec1808e63 100644
--- a/src/Avalonia.Controls/VirtualizingStackPanel.cs
+++ b/src/Avalonia.Controls/VirtualizingStackPanel.cs
@@ -493,8 +493,7 @@ namespace Avalonia.Controls
                 c = c?.GetVisualParent();
             }
 
-
-            return viewport;
+            return viewport.Intersect(new Rect(0, 0, double.PositiveInfinity, double.PositiveInfinity));
         }
 
         private void RealizeElements(