From 55275e09def1f8830ce3cafd071529ab600ea0f0 Mon Sep 17 00:00:00 2001
From: Steven Kirk <grokys@gmail.com>
Date: Thu, 9 Jan 2020 10:01:53 +0100
Subject: [PATCH] =?UTF-8?q?Fix=20stack=20layout=20arrange=20when=20items?=
 =?UTF-8?q?=20use=20stretch=20and=20final=20size=20is=20mor=E2=80=A6?=
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…e than desired size.

Ported from https://github.com/microsoft/microsoft-ui-xaml/commit/f37ebd5bb21e6d4d7b3bb4228fb22a47d3c33b85
---
 src/Avalonia.Layout/FlowLayoutAlgorithm.cs | 18 +++++++++++++++---
 src/Avalonia.Layout/StackLayout.cs         |  1 +
 src/Avalonia.Layout/UniformGridLayout.cs   |  1 +
 3 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/src/Avalonia.Layout/FlowLayoutAlgorithm.cs b/src/Avalonia.Layout/FlowLayoutAlgorithm.cs
index 7343f4a6e9..7f44c80a64 100644
--- a/src/Avalonia.Layout/FlowLayoutAlgorithm.cs
+++ b/src/Avalonia.Layout/FlowLayoutAlgorithm.cs
@@ -116,10 +116,11 @@ namespace Avalonia.Layout
         public Size Arrange(
             Size finalSize,
             VirtualizingLayoutContext context,
+            bool isWrapping,
             LineAlignment lineAlignment,
             string layoutId)
         {
-            ArrangeVirtualizingLayout(finalSize, lineAlignment, layoutId);
+            ArrangeVirtualizingLayout(finalSize, lineAlignment, isWrapping, layoutId);
 
             return new Size(
                 Math.Max(finalSize.Width, _lastExtent.Width),
@@ -546,6 +547,7 @@ namespace Avalonia.Layout
         private void ArrangeVirtualizingLayout(
             Size finalSize,
             LineAlignment lineAlignment,
+            bool isWrapping,
             string layoutId)
         {
             // Walk through the realized elements one line at a time and 
@@ -565,7 +567,7 @@ namespace Avalonia.Layout
                     if (_orientation.MajorStart(currentBounds) != currentLineOffset)
                     {
                         spaceAtLineEnd = _orientation.Minor(finalSize) - _orientation.MinorStart(previousElementBounds) - _orientation.MinorSize(previousElementBounds);
-                        PerformLineAlignment(i - countInLine, countInLine, spaceAtLineStart, spaceAtLineEnd, currentLineSize, lineAlignment, layoutId);
+                        PerformLineAlignment(i - countInLine, countInLine, spaceAtLineStart, spaceAtLineEnd, currentLineSize, lineAlignment, isWrapping, finalSize, layoutId);
                         spaceAtLineStart = _orientation.MinorStart(currentBounds);
                         countInLine = 0;
                         currentLineOffset = _orientation.MajorStart(currentBounds);
@@ -582,7 +584,7 @@ namespace Avalonia.Layout
                 if (countInLine > 0)
                 {
                     var spaceAtEnd = _orientation.Minor(finalSize) - _orientation.MinorStart(previousElementBounds) - _orientation.MinorSize(previousElementBounds);
-                    PerformLineAlignment(realizedElementCount - countInLine, countInLine, spaceAtLineStart, spaceAtEnd, currentLineSize, lineAlignment, layoutId);
+                    PerformLineAlignment(realizedElementCount - countInLine, countInLine, spaceAtLineStart, spaceAtEnd, currentLineSize, lineAlignment, isWrapping, finalSize, layoutId);
                 }
             }
         }
@@ -596,6 +598,8 @@ namespace Avalonia.Layout
             double spaceAtLineEnd,
             double lineSize,
             LineAlignment lineAlignment,
+            bool isWrapping,
+            Size finalSize,
             string layoutId)
         {
             for (int rangeIndex = lineStartIndex; rangeIndex < lineStartIndex + countInLine; ++rangeIndex)
@@ -661,6 +665,14 @@ namespace Avalonia.Layout
                 }
 
                 bounds = bounds.Translate(-_lastExtent.Position);
+
+                if (!isWrapping)
+                {
+                    _orientation.SetMinorSize(
+                        ref bounds,
+                        Math.Max(_orientation.MinorSize(bounds), _orientation.Minor(finalSize)));
+                }
+
                 var element = _elementManager.GetAt(rangeIndex);
                 element.Arrange(bounds);
             }
diff --git a/src/Avalonia.Layout/StackLayout.cs b/src/Avalonia.Layout/StackLayout.cs
index a3fe80fab7..3c3729272c 100644
--- a/src/Avalonia.Layout/StackLayout.cs
+++ b/src/Avalonia.Layout/StackLayout.cs
@@ -279,6 +279,7 @@ namespace Avalonia.Layout
             var value = GetFlowAlgorithm(context).Arrange(
                finalSize,
                context,
+               false,
                FlowLayoutAlgorithm.LineAlignment.Start,
                LayoutId);
 
diff --git a/src/Avalonia.Layout/UniformGridLayout.cs b/src/Avalonia.Layout/UniformGridLayout.cs
index 16d21508a9..86dc21bd19 100644
--- a/src/Avalonia.Layout/UniformGridLayout.cs
+++ b/src/Avalonia.Layout/UniformGridLayout.cs
@@ -446,6 +446,7 @@ namespace Avalonia.Layout
             var value = GetFlowAlgorithm(context).Arrange(
                finalSize,
                context,
+               true,
                (FlowLayoutAlgorithm.LineAlignment)_itemsJustification,
                LayoutId);
             return new Size(value.Width, value.Height);