fix(textbox): losing focus on PointerUp when inside a Popup on WASM

src/SamplesApp/UITests.Shared/UITests.Shared.projitems

@@ -1414,6 +1414,10 @@
       <SubType>Designer</SubType>
       <Generator>MSBuild:Compile</Generator>
     </Page>
+    <Page Include="$(MSBuildThisFileDirectory)Windows_UI_Xaml_Controls\AutoSuggestBoxTests\AutoSuggestBox_PopupFocus.xaml">
+      <SubType>Designer</SubType>
+      <Generator>MSBuild:Compile</Generator>
+    </Page>
     <Page Include="$(MSBuildThisFileDirectory)Windows_UI_Xaml_Controls\AutoSuggestBoxTests\AutoSuggestBox_Icons.xaml">
       <SubType>Designer</SubType>
       <Generator>MSBuild:Compile</Generator>
@@ -6558,6 +6562,9 @@
     <Compile Include="$(MSBuildThisFileDirectory)Windows_UI_Xaml_Controls\AutoSuggestBoxTests\AutoSuggestBox_Description.xaml.cs">
       <DependentUpon>AutoSuggestBox_Description.xaml</DependentUpon>
     </Compile>
+    <Compile Include="$(MSBuildThisFileDirectory)Windows_UI_Xaml_Controls\AutoSuggestBoxTests\AutoSuggestBox_PopupFocus.xaml.cs">
+      <DependentUpon>AutoSuggestBox_PopupFocus.xaml</DependentUpon>
+    </Compile>
     <Compile Include="$(MSBuildThisFileDirectory)Windows_UI_Xaml_Controls\AutoSuggestBoxTests\AutoSuggestBox_Icons.xaml.cs">
       <DependentUpon>AutoSuggestBox_Icons.xaml</DependentUpon>
     </Compile>

src/SamplesApp/UITests.Shared/Windows_UI_Xaml_Controls/AutoSuggestBoxTests/AutoSuggestBox_PopupFocus.xaml

@@ -0,0 +1,38 @@
+<Page
+    x:Class="UITests.Windows_UI_Xaml_Controls.AutoSuggestBoxTests.AutoSuggestBox_PopupFocus"
+    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+    xmlns:local="using:UITests.Windows_UI_Xaml_Controls.AutoSuggestBoxTests"
+    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
+    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+    mc:Ignorable="d"
+    Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
+
+	<StackPanel>
+		<Button Content="Click me">
+			<Button.Flyout>
+				<Flyout>
+					<StackPanel>
+						<TextBlock>
+							Repro Steps:
+							<LineBreak/>
+							1. Click on the TextBox below. The textbox should look focused
+							<LineBreak/>
+							(i.e.light blue bottom border).
+							<LineBreak/>
+							2. Type the character "T". A suggestions list should pop up
+							<LineBreak/>
+							with a single item, "test".
+						</TextBlock>
+						<AutoSuggestBox PlaceholderText="type some text">
+							<AutoSuggestBox.Items>
+								<x:String>test</x:String>
+							</AutoSuggestBox.Items>
+						</AutoSuggestBox>
+						<TextBox />
+					</StackPanel>
+				</Flyout>
+			</Button.Flyout>
+		</Button>
+	</StackPanel>
+</Page>

src/SamplesApp/UITests.Shared/Windows_UI_Xaml_Controls/AutoSuggestBoxTests/AutoSuggestBox_PopupFocus.xaml.cs

@@ -0,0 +1,13 @@
+using Uno.UI.Samples.Controls;
+using Microsoft.UI.Xaml.Controls;
+
+namespace UITests.Windows_UI_Xaml_Controls.AutoSuggestBoxTests;
+
+[Sample("AutoSuggestBox", IsManualTest = true)]
+public sealed partial class AutoSuggestBox_PopupFocus : Page
+{
+	public AutoSuggestBox_PopupFocus()
+	{
+		this.InitializeComponent();
+	}
+}

src/Uno.UI/UI/Xaml/Controls/ScrollViewer/ScrollViewer.MuxInternal.cs

@@ -179,6 +179,13 @@ protected override void OnPointerReleased(PointerRoutedEventArgs args)
 
 		private static bool ScrollContentControl_SetFocusOnFlyoutLightDismissPopupByPointer(UIElement pScrollContentControl)
 		{
+#if __CROSSRUNTIME__
+			if ((pScrollContentControl as ScrollViewer)?.DisableSetFocusOnPopupByPointer ?? false)
+			{
+				return false;
+			}
+#endif
+
 			PopupRoot? pPopupRoot = null;
 			Popup? pPopup = null;
 

src/Uno.UI/UI/Xaml/Controls/ScrollViewer/ScrollViewer.cs

@@ -593,6 +593,17 @@ public double HorizontalOffset
 			);
 		#endregion
 
+#if __CROSSRUNTIME__
+		/// <summary>
+		/// This is specifically added for ScrollViewers inside TextBoxes and specifically for WASM
+		/// On WASM, a click on a TextBox inside a popup shifts focus to the Popup instead of the TextBox
+		/// as a result of ScrollContentControl_SetFocusOnFlyoutLightDismissPopupByPointer.
+		/// This is only a problem on WASM because we don't capture the pointer when pressing inside a TextBox
+		/// <seealso cref="TextBox.IsPointerCaptureRequired"/>.
+		/// </summary>
+		internal bool DisableSetFocusOnPopupByPointer { get; set; }
+#endif
+
 		private readonly SerialDisposable _sizeChangedSubscription = new SerialDisposable();
 
 #pragma warning disable 649 // unused member for Unit tests

src/Uno.UI/UI/Xaml/Controls/TextBox/TextBox.Uno.cs

@@ -28,6 +28,12 @@ public bool IsPointerCaptureRequired
 			new FrameworkPropertyMetadata(
 				// We should not capture the pointer on WASM by default because it would prevent the user from scrolling through text on selection.
 				// See https://github.com/unoplatform/uno/pull/16982, https://issues.chromium.org/issues/344491566
-				false));
+				false, static (dO, args) =>
+				{
+					if (((TextBox)dO)._contentElement is ScrollViewer sv)
+					{
+						sv.DisableSetFocusOnPopupByPointer = !(bool)args.NewValue;
+					}
+				}));
 #endif
 }

src/Uno.UI/UI/Xaml/Controls/TextBox/TextBox.cs

@@ -169,6 +169,10 @@ private protected override void OnLoaded()
 					scrollViewer.HorizontalScrollBarVisibility = ScrollBarVisibility.Disabled; // The template sets this to Hidden
 					scrollViewer.VerticalScrollBarVisibility = ScrollBarVisibility.Auto; // The template sets this to Hidden
 				}
+
+#if __WASM__
+				scrollViewer.DisableSetFocusOnPopupByPointer = !IsPointerCaptureRequired;
+#endif
 #endif
 			}
 		}