Freeze the preview tab on drag and add Ctrl+W tab close

Pinning the One immovably at index 0 made a drag on it a dead no-op, which reads as a broken tab. Dragging now freezes it instead: pulling the tab out is itself the gesture to keep it, mirroring the snowflake and right-click Freeze, and the next tree selection forges a fresh preview at index 0. Index-0 protection and the self-healing re-assert now apply only while the One is still the preview.

Ctrl+W closes the active document; closing the One drops the cached decompiler viewmodel so the next selection rebuilds it. Long type signatures no longer stretch a tab without bound -- the on-tab title is capped and ellipsised with the full title in a tooltip, and the close button names its shortcut.

ILSpy.Tests/Docking/PreviewTabPromotionTests.cs

@@ -538,6 +538,82 @@ public class PreviewTabPromotionTests
 			"after the Theme-copy refactor the custom class-based styling is unused; the Theme drives all visuals");
 	}
 
+	[AvaloniaTest]
+	public async Task Close_Button_Has_A_Ctrl_W_Tooltip()
+	{
+		// Dock's tab template gives the close button no tooltip. PreviewTabFreezeButtonBehavior
+		// names its Ctrl+W shortcut so the gesture is discoverable on hover.
+		var (window, vm) = await TestHarness.BootAsync(3);
+
+		// Open a carve-out so the close button is realised (single-tab scenario hides it).
+		var typeNode = vm.AssemblyTreeModel.FindNode<TypeTreeNode>(
+			"System.Linq", "System.Linq", "System.Linq.Enumerable");
+		vm.DockWorkspace.OpenNodeInNewTab(typeNode);
+		TestCapture.Step("carve-out-tab-opened");
+
+		await Waiters.WaitForAsync(() => window.GetVisualDescendants().OfType<DocumentTabStripItem>().Count() >= 2,
+			System.TimeSpan.FromSeconds(10));
+		global::Avalonia.Threading.Dispatcher.UIThread.RunJobs();
+
+		var factory = (ILSpyDockFactory)vm.DockWorkspace.Factory;
+		var mainTabItem = window.GetVisualDescendants().OfType<DocumentTabStripItem>()
+			.Single(item => ReferenceEquals(item.DataContext, factory.MainTab));
+
+		var closeButton = mainTabItem.GetVisualDescendants()
+			.OfType<global::Avalonia.Controls.Button>()
+			.FirstOrDefault(b => (b.Tag as string) != "PreviewTabFreezeButton");
+		closeButton.Should().NotBeNull("baseline: close button exists as a sibling of the freeze");
+
+		global::Avalonia.Controls.ToolTip.GetTip(closeButton!).Should().Be("Close (Ctrl+W)",
+			"the close button must name its Ctrl+W shortcut on hover");
+	}
+
+	[AvaloniaTest]
+	public async Task Ctrl_W_Closes_The_Active_Document_And_Reforges_The_One()
+	{
+		// Ctrl+W (CloseActiveDocumentCommand) closes whatever document is active. Closing a frozen
+		// carve-out leaves the One untouched; closing the One drops the cached decompiler VM so the
+		// next tree selection forges a fresh preview at index 0.
+		var (_, vm) = await TestHarness.BootAsync(3);
+		var factory = (ILSpyDockFactory)vm.DockWorkspace.Factory;
+		var docs = vm.DockWorkspace.Documents!;
+
+		var typeA = vm.AssemblyTreeModel.FindNode<TypeTreeNode>(
+			"System.Linq", "System.Linq", "System.Linq.Enumerable");
+		vm.AssemblyTreeModel.SelectNode(typeA);
+		vm.DockWorkspace.SettleSelection();
+		var theOne = factory.MainTab!;
+		theOne.IsPreview.Should().BeTrue("precondition: the One starts as the preview");
+
+		// A frozen carve-out keeps the dock non-empty so the One isn't the last tab when closed.
+		var typeC = vm.AssemblyTreeModel.FindNode<TypeTreeNode>(
+			"System.Private.Uri", "System", "System.Uri");
+		vm.DockWorkspace.OpenNodeInNewTab(typeC);
+		var frozen = docs.VisibleDockables!.OfType<ContentTabPage>().Last(t => t.SourceNode == typeC);
+
+		// Closing the One while it is active removes it from the dock; the frozen tab survives.
+		factory.SetActiveDockable(theOne);
+		vm.DockWorkspace.CloseActiveDocument();
+		docs.VisibleDockables!.Should().NotContain(theOne, "Ctrl+W closes the One when it is active");
+		docs.VisibleDockables!.Should().Contain(frozen, "the frozen carve-out must survive closing the One");
+
+		// The next selection forges a brand-new One (the closed one is not resurrected).
+		var typeD = vm.AssemblyTreeModel.FindNode<TypeTreeNode>(
+			"System.Private.Uri", "System", "System.UriBuilder");
+		vm.AssemblyTreeModel.SelectNode(typeD);
+		vm.DockWorkspace.SettleSelection();
+		var freshOne = factory.MainTab;
+		freshOne.Should().NotBeNull("a fresh One is forged on the next selection");
+		freshOne.Should().NotBeSameAs(theOne, "the forged One is a new instance, not the closed tab");
+		freshOne!.IsPreview.Should().BeTrue("the forged One is a preview tab");
+
+		// Closing a frozen carve-out leaves the (fresh) One untouched.
+		factory.SetActiveDockable(frozen);
+		vm.DockWorkspace.CloseActiveDocument();
+		docs.VisibleDockables!.Should().NotContain(frozen, "Ctrl+W closes the active frozen tab");
+		factory.MainTab.Should().BeSameAs(freshOne, "closing a frozen tab must not disturb the One");
+	}
+
 	[AvaloniaTest]
 	public async Task Tree_Selection_While_Frozen_Tab_Active_Reuses_The_One()
 	{
@@ -622,10 +698,11 @@ public class PreviewTabPromotionTests
 	}
 
 	[AvaloniaTest]
-	public async Task Preview_Cannot_Be_Reordered_Out_Of_Slot_0()
+	public async Task Dragging_The_Preview_Freezes_It()
 	{
-		// The in-strip reorder drag commits through the same-dock MoveDockable; it's overridden to
+		// The in-strip reorder drag commits through the same-dock MoveDockable; it's overridden so
-		// refuse moving the One out of slot 0. Drive that commit directly (what ItemDragHelper does).
+		// that dragging the One freezes it (instead of refusing the move). Drive that commit
+		// directly (what ItemDragHelper does).
 		var (_, vm) = await TestHarness.BootAsync(3);
 		var factory = (ILSpyDockFactory)vm.DockWorkspace.Factory;
 		var docs = vm.DockWorkspace.Documents!;
@@ -635,6 +712,7 @@ public class PreviewTabPromotionTests
 		vm.AssemblyTreeModel.SelectNode(typeA);
 		vm.DockWorkspace.SettleSelection();
 		var theOne = factory.MainTab!;
+		theOne.IsPreview.Should().BeTrue("precondition: the One starts as the preview");
 		var typeC = vm.AssemblyTreeModel.FindNode<TypeTreeNode>(
 			"System.Private.Uri", "System", "System.Uri");
 		vm.DockWorkspace.OpenNodeInNewTab(typeC);
@@ -643,8 +721,10 @@ public class PreviewTabPromotionTests
 
 		factory.MoveDockable(docs, theOne, frozen);
 
-		docs.VisibleDockables!.IndexOf(theOne).Should().Be(0,
+		theOne.IsPreview.Should().BeFalse(
-			"the One must stay at index 0 -- it is immovable");
+			"dragging the One must freeze it -- it becomes an ordinary, movable tab");
+		factory.MainTab.Should().BeSameAs(theOne,
+			"freeze-on-drag does not rotate MainTab; the next tree selection forges a fresh One");
 	}
 
 	[AvaloniaTest]

ILSpy/App.axaml

@@ -76,7 +76,7 @@
                     <SolidColorBrush x:Key="ILSpy.PreviewTabHoverBackground" Color="#BB8FCE" />
                     <!-- Focused tool pane: a subtle neutral header tint + readable title, instead of
                          the theme's saturated system accent. -->
-                    <SolidColorBrush x:Key="ILSpy.ToolChromeActiveHeaderBackground" Color="#DCDCDC" />
+                    <SolidColorBrush x:Key="ILSpy.ToolChromeActiveHeaderBackground" Color="#C4C4C4" />
                     <SolidColorBrush x:Key="ILSpy.ToolChromeActiveTitleForeground" Color="#1E1E1E" />
                     <SolidColorBrush x:Key="ILSpy.FoldingMarkerBackground" Color="#FFFFE1" />
                     <SolidColorBrush x:Key="ILSpy.FoldingMarkerForeground" Color="#808080" />
@@ -279,6 +279,14 @@
             <Setter Property="Background" Value="{DynamicResource ILSpy.DockTabItemBackground}" />
             <Setter Property="Foreground" Value="{DynamicResource ILSpy.DockTabItemForeground}" />
         </Style>
+        <!-- Full title in a tooltip on every document tab. The on-tab ellipsis is applied to the
+             realised title TextBlock by PreviewTabFreezeButtonBehavior, NOT with a descendant
+             selector here: a `DocumentTabStripItem TextBlock` selector also matched the tooltip's
+             own TextBlock and trimmed it to the same ellipsised text. Tool panes have short fixed
+             names, so this is document-only. -->
+        <Style Selector="dockControls|DocumentTabStripItem">
+            <Setter Property="ToolTip.Tip" Value="{Binding Title, Mode=OneWay, x:CompileBindings=False}" />
+        </Style>
         <!-- A merely-selected (but not focused) tab gets the seam-matching fill. The active
              tab keeps Dock's accent highlight (see below). Splitting the two states is
              required: an application-level Style outranks Dock's DocumentTabStripItem

ILSpy/Docking/DockWorkspace.cs

@@ -91,6 +91,11 @@ namespace ILSpy.Docking
 		/// </summary>
 		public IRelayCommand ShowSearchCommand { get; }
 
+		/// <summary>Closes the active document tab. Wired to Ctrl+W on the main window. The
+		/// documents dock only ever holds <see cref="ContentTabPage"/>s, so this never touches a
+		/// tool pane.</summary>
+		public IRelayCommand CloseActiveDocumentCommand { get; }
+
 		// Read-only history snapshots for the Back/Forward split-button dropdowns; oldest-first.
 		// The UI reverses these for newest-first display.
 		public IReadOnlyList<NavigationEntry> BackHistory => history.BackEntries;
@@ -165,6 +170,7 @@ namespace ILSpy.Docking
 			NavigateToHistoryCommand = new RelayCommand<NavigationEntry>(NavigateToHistory,
 				entry => entry != null && (history.BackEntries.Contains(entry) || history.ForwardEntries.Contains(entry)));
 			ShowSearchCommand = new RelayCommand(ExecuteShowSearch);
+			CloseActiveDocumentCommand = new RelayCommand(CloseActiveDocument);
 			using (ILSpy.AppEnv.AppLog.Phase("ILSpyDockFactory ctor + CreateLayout + InitLayout"))
 			{
 				using (ILSpy.AppEnv.AppLog.Phase("ILSpyDockFactory ctor"))
@@ -1204,6 +1210,19 @@ namespace ILSpy.Docking
 				factory.CloseDockable(doc);
 		}
 
+		/// <summary>Closes the active document tab (Ctrl+W). The documents dock only holds
+		/// <see cref="ContentTabPage"/>s, so tool panes are never affected. Closing the One drops
+		/// the cached decompiler viewmodel so the next selection forges a fresh preview tab.</summary>
+		public void CloseActiveDocument()
+		{
+			if (factory.Documents?.ActiveDockable is not ContentTabPage active)
+				return;
+			bool wasTheOne = ReferenceEquals(active, factory.MainTab);
+			factory.CloseDockable(active);
+			if (wasTheOne)
+				decompilerContent = null;
+		}
+
 		public void ResetLayout()
 		{
 			// Rebuild from the factory's default layout. The active tree node, if any, will be

ILSpy/Docking/ILSpyDockFactory.cs

@@ -83,20 +83,25 @@ namespace ILSpy.Docking
 			return fresh;
 		}
 
-		// The One is immovable at documents-dock index 0. A within-strip reorder drag commits
+		// The One sits at documents-dock index 0. A within-strip reorder drag commits through this
-		// through this same-dock MoveDockable (Dock's DocumentTabStripItem/ItemDragHelper does NOT
+		// same-dock MoveDockable (Dock's DocumentTabStripItem/ItemDragHelper does NOT consult
-		// consult IDockable.CanDrag), so overriding it is the choke point that pins the One to
+		// IDockable.CanDrag), so this override is the choke point: dragging the One FREEZES it (it
-		// slot 0 and keeps frozen tabs to its right.
+		// then moves like any other tab), and while it is still the preview no frozen tab may slip
+		// in front of it.
 		public override void MoveDockable(IDock dock, IDockable sourceDockable, IDockable targetDockable)
 		{
 			if (ReferenceEquals(dock, Documents))
 			{
-				// Never drag the One out of slot 0.
+				// Dragging the One freezes it (replacing the old "refuse the move" behaviour): it
-				if (ReferenceEquals(sourceDockable, MainTab))
+				// stops being the preview slot and lands wherever it's dropped; the next tree
-					return;
+				// selection forges a fresh One at index 0.
-				// A frozen tab must not land at or before the One: retarget to the tab at index 1
+				if (ReferenceEquals(sourceDockable, MainTab) && MainTab is { IsPreview: true })
-				// so the source lands at position 1, not 0.
+				{
-				if (ReferenceEquals(targetDockable, MainTab))
+					FreezeCurrentMainTab();
+				}
+				// While the One is still the preview, a frozen tab must not land at or before it:
+				// retarget to the tab at index 1 so the source lands at position 1, not 0.
+				else if (ReferenceEquals(targetDockable, MainTab) && MainTab is { IsPreview: true })
 				{
 					var kids = dock.VisibleDockables;
 					if (kids is { Count: > 1 })
@@ -108,21 +113,23 @@ namespace ILSpy.Docking
 			base.MoveDockable(dock, sourceDockable, targetDockable);
 		}
 
-		// Cross-dock move: never pull the One into another document dock (only reachable if the
+		// Cross-dock move (only reachable if the document area is ever split): dragging the One out
-		// document area is ever split).
+		// freezes it too, consistent with the in-strip case.
 		public override void MoveDockable(IDock sourceDock, IDock targetDock, IDockable sourceDockable, IDockable? targetDockable)
 		{
-			if (ReferenceEquals(sourceDockable, MainTab))
+			if (ReferenceEquals(sourceDockable, MainTab) && MainTab is { IsPreview: true })
-				return;
+				FreezeCurrentMainTab();
 			base.MoveDockable(sourceDock, targetDock, sourceDockable, targetDockable);
 		}
 
-		// Self-healing insurance: whatever drag path ran, re-assert the One at index 0. Idempotent
+		// Self-healing insurance: re-assert the One at index 0 after any drag -- but ONLY while it is
-		// and cheap -- guards against a future Dock version routing a reorder past MoveDockable.
+		// still the preview. Once dragged (which freezes it) it's an ordinary tab and must stay where
+		// the user dropped it. Idempotent; guards against a future Dock version routing a reorder
+		// past MoveDockable.
 		public override void OnDockableMoved(IDockable? dockable)
 		{
 			base.OnDockableMoved(dockable);
-			if (MainTab is not { } one || Documents?.VisibleDockables is not { } kids)
+			if (MainTab is not { IsPreview: true } one || Documents?.VisibleDockables is not { } kids)
 				return;
 			int idx = kids.IndexOf(one);
 			if (idx > 0)

ILSpy/Themes/PreviewTabFreezeButtonBehavior.cs

@@ -102,6 +102,17 @@ namespace ILSpy.Themes
 			// paint on top of it.
 			titleStack.ClipToBounds = true;
 
+			// Cap the title and ellipsise overruns so a long type signature can't make a giant tab;
+			// the full title is surfaced in the tab tooltip (App.axaml). Applied to the specific
+			// realised title TextBlock here rather than via a `DocumentTabStripItem TextBlock` style
+			// selector, which also matched -- and trimmed -- the tooltip's own TextBlock.
+			var titleText = titleStack.GetVisualDescendants().OfType<TextBlock>().FirstOrDefault();
+			if (titleText is not null)
+			{
+				titleText.MaxWidth = 240;
+				titleText.TextTrimming = TextTrimming.CharacterEllipsis;
+			}
+
 			// Snowflake glyph for "freeze" (Font Awesome Free v7 "snowflake", CC-BY-4.0). A filled
 			// vector Path (not a font glyph): a Segoe Fluent fallback was Windows-only and rendered
 			// as tofu on Linux / macOS. Fill is bound to the tab Foreground so the glyph inherits
@@ -147,6 +158,11 @@ namespace ILSpy.Themes
 			if (closeButton?.Theme is { } closeTheme)
 				freezeButton.Theme = closeTheme;
 			ToolTip.SetTip(freezeButton, "Freeze tab");
+			// The close button carries no tooltip from Dock's template; name its Ctrl+W shortcut.
+			// TryInject runs for every document tab (the freeze button is injected on all of them,
+			// just hidden when not the One), so this covers preview and frozen tabs alike.
+			if (closeButton is not null)
+				ToolTip.SetTip(closeButton, "Close (Ctrl+W)");
 
 			// IsVisible follows IsPreview — the button hides once the tab is frozen.
 			freezeButton.Bind(Visual.IsVisibleProperty, new Binding(nameof(ContentTabPage.IsPreview)) {

ILSpy/Views/MainWindow.axaml

@@ -28,6 +28,8 @@
 		     "search box" gesture VS uses. Both bring the bottom search pane to focus. -->
 		<KeyBinding Gesture="Ctrl+Shift+F" Command="{Binding DockWorkspace.ShowSearchCommand}" />
 		<KeyBinding Gesture="Ctrl+E" Command="{Binding DockWorkspace.ShowSearchCommand}" />
+		<!-- Close the active document tab (documents only; tool panes are unaffected). -->
+		<KeyBinding Gesture="Ctrl+W" Command="{Binding DockWorkspace.CloseActiveDocumentCommand}" />
 	</Window.KeyBindings>
 
 	<DockPanel>