Fix #4030: Enter did not activate the selected tree row

Avalonia 12 treats plain Enter/Space on a ListBoxItem as selection
input: the container marks the KeyDown handled before it bubbles, so
SharpTreeView.OnKeyDown never saw the keys and its activation handling
(navigate to the member from an analyzer row, toggle a checkable row)
was dead. Override ShouldTriggerSelection -- the extension point added
for this in Avalonia 12 -- to suppress the selection trigger exactly
for the case OnKeyDown activates instead: a single selected row that
is the row the key landed on. Multi-row selections keep the default
collapse-to-focused-row behaviour.

Assisted-by: Claude:claude-fable-5:Claude Code

ILSpy.Tests/Analyzers/AnalyzerTreeKeyboardTests.cs

@@ -70,6 +70,39 @@ public class AnalyzerTreeKeyboardTests
 			description: "Right must expand the node via SharpTreeView.OnKeyDown on the analyzer tree");
 	}
 
+	[AvaloniaTest]
+	public async Task Enter_Activates_The_Selected_Analyzer_Node()
+	{
+		// Enter on a single selected analyzer row activates it -- for an entity node that means
+		// navigating to the member's home in the assembly tree, like 10.x did. The key must reach
+		// SharpTreeView.OnKeyDown: the container is a ListBoxItem, and Avalonia's default key
+		// selection triggers treat Enter/Space as selection input and mark the event handled
+		// before it bubbles, so SharpTreeView suppresses that trigger for the activation case.
+		var (window, vm) = await TestHarness.BootAsync(3);
+		var dockWorkspace = AppComposition.Current.GetExport<DockWorkspace>();
+		var analyzerVm = AppComposition.Current.GetExport<AnalyzerTreeViewModel>();
+
+		var typeNode = vm.AssemblyTreeModel.FindNode<TypeTreeNode>(
+			"System.Linq", "System.Linq", "System.Linq.Enumerable");
+		var entity = (ITypeDefinition)typeNode.Member!;
+		var analyzed = analyzerVm.Analyze(entity);
+
+		dockWorkspace.ShowToolPane(AnalyzerTreeViewModel.PaneContentId);
+		var view = await window.WaitForComponent<ICSharpCode.ILSpy.Analyzers.AnalyzerTreeView>();
+		var tree = await view.WaitForComponent<ICSharpCode.ILSpy.Controls.TreeView.SharpTreeView>();
+		tree.SelectedItem = analyzed;
+		Dispatcher.UIThread.RunJobs();
+		tree.FocusNode(analyzed);
+		Dispatcher.UIThread.RunJobs();
+
+		((object?)vm.AssemblyTreeModel.SelectedItem).Should().NotBeSameAs(typeNode,
+			"precondition: the assembly tree must not already sit on the target node");
+
+		window.KeyPress(Key.Enter, RawInputModifiers.None, PhysicalKey.Enter, null);
+		await Waiters.WaitForAsync(() => ReferenceEquals(vm.AssemblyTreeModel.SelectedItem, typeNode),
+			description: "Enter must activate the analyzer node and select the type in the assembly tree");
+	}
+
 	[AvaloniaTest]
 	public async Task Ctrl_R_Analyzes_The_Selected_Member()
 	{

ILSpy/Controls/TreeView/SharpTreeView.cs

@@ -295,6 +295,27 @@ namespace ICSharpCode.ILSpy.Controls.TreeView
 			scrollViewer.Offset = new Vector(scrollViewer.Offset.X, newOffsetY);
 		}
 
+		/// <summary>
+		/// Avalonia's default key selection triggers treat plain Enter/Space as selection input:
+		/// the ListBoxItem container marks the KeyDown handled before it bubbles here, so the
+		/// activation handling in <see cref="OnKeyDown"/> would never see those keys. Suppress the
+		/// selection trigger exactly for the case OnKeyDown activates instead -- a single selected
+		/// row that is the row the key landed on. Multi-row selections keep the default behaviour
+		/// (Enter/Space collapses the selection to the focused row).
+		/// </summary>
+		protected override bool ShouldTriggerSelection(Visual selectable, KeyEventArgs eventArgs)
+		{
+			if (eventArgs.KeyModifiers == KeyModifiers.None
+				&& eventArgs.Key is Key.Enter or Key.Space
+				&& selectable is SharpTreeViewItem { Node: { } node }
+				&& SelectedItems?.Count == 1
+				&& ReferenceEquals(SelectedItem, node))
+			{
+				return false;
+			}
+			return base.ShouldTriggerSelection(selectable, eventArgs);
+		}
+
 		protected override void OnKeyDown(KeyEventArgs e)
 		{
 			// Ctrl+A select-all must work on the first press even before a current item is