Centralize MEF export lookup in AppComposition.TryGetExport

Eleven call sites each wrapped AppComposition.Current.GetExport<T>() in a
try/catch that returned null, to survive design-time previews and minimal
test hosts where the composition host isn't up. Replace those copies with
one AppComposition.TryGetExport<T>()/TryGetExports<T>() and inline it at
every site, deleting the per-class wrappers.

The shared helper does not blanket-swallow: host absence is checked
explicitly (the static field, not the throwing Current), and the built-in
TryGetExport(out) reports a missing export as false. So an export that is
present but genuinely broken now surfaces its activation error instead of
being silently turned into null.

Assisted-by: Claude:claude-opus-4-8:Claude Code

ILSpy/AppEnv/AppComposition.cs

@@ -18,8 +18,10 @@
 
 using System;
 using System.Collections.Generic;
+using System.Composition;
 using System.Composition.Hosting;
 using System.IO;
+using System.Linq;
 using System.Reflection;
 using System.Runtime.Loader;
 
@@ -45,6 +47,23 @@ namespace ILSpy.AppEnv
 		public static CompositionHost Current
 			=> current ?? throw new InvalidOperationException("Composition host is not yet initialized.");
 
+		/// <summary>
+		/// Resolves a single MEF export, or returns <see langword="null"/> when the composition host
+		/// isn't initialized yet (design-time previewer, headless pre-boot) or no such export exists.
+		/// Unlike a blanket try/catch this does NOT swallow composition/activation errors: host
+		/// absence is checked explicitly and the built-in <c>TryGetExport</c> reports a missing export
+		/// as <see langword="false"/>, so a genuinely broken export still surfaces its exception.
+		/// </summary>
+		public static T? TryGetExport<T>() where T : class
+			=> current is { } host && host.TryGetExport(out T? export) ? export : null;
+
+		/// <summary>
+		/// Resolves all MEF exports of <typeparamref name="T"/>, or an empty sequence when the host
+		/// isn't initialized yet. <see cref="TryGetExport{T}"/> for the single-export case.
+		/// </summary>
+		public static IEnumerable<T> TryGetExports<T>() where T : class
+			=> current?.GetExports<T>() ?? Enumerable.Empty<T>();
+
 		public static CompositionHost Initialize()
 		{
 			RegisterPluginResolver();

ILSpy/AssemblyTree/AssemblyTreeModel.cs

@@ -183,7 +183,7 @@ namespace ILSpy.AssemblyTree
 			{
 				// Open the definition in a fresh carve-out tab instead of replacing the current view
 				// (e.g. "Decompile to new tab" on a symbol in the code).
-				TryGetExport<Docking.DockWorkspace>()?.OpenNodeInNewTab(resolved);
+				AppEnv.AppComposition.TryGetExport<Docking.DockWorkspace>()?.OpenNodeInNewTab(resolved);
 			}
 			else
 			{
@@ -194,18 +194,11 @@ namespace ILSpy.AssemblyTree
 			// paints local-reference marks on every match once the new Text lands.
 			if (e.Source is null)
 				return;
-			var dockWorkspace = TryGetExport<Docking.DockWorkspace>();
+			var dockWorkspace = AppEnv.AppComposition.TryGetExport<Docking.DockWorkspace>();
 			if (dockWorkspace?.ActiveDecompilerTab is { } decompTab)
 				decompTab.HighlightedReference = e.Source;
 		}
 
-		static T? TryGetExport<T>() where T : class
-		{
-			try
-			{ return AppEnv.AppComposition.Current.GetExport<T>(); }
-			catch { return null; }
-		}
-
 		// True while the SelectedItem setter is replacing the collection via Clear()+Add();
 		// suppresses the selection-changed fan-out until the final state is in place so consumers
 		// never observe the transient empty/multi mid-replace.
@@ -455,7 +448,7 @@ namespace ILSpy.AssemblyTree
 		// and its instance IS the AboutCommand, so we can drive its welcome path directly.
 		void ShowAboutWelcomePage()
 		{
-			var registry = TryGetExport<MainMenuCommandRegistry>();
+			var registry = AppEnv.AppComposition.TryGetExport<MainMenuCommandRegistry>();
 			var export = registry?.Commands
 				.FirstOrDefault(c => c.Metadata.Header == nameof(ICSharpCode.ILSpy.Properties.Resources._About))
 				?.CreateExport();
@@ -1050,7 +1043,7 @@ namespace ILSpy.AssemblyTree
 				var removed = new HashSet<LoadedAssembly>(oldItems.OfType<LoadedAssembly>());
 				if (removed.Count > 0)
 				{
-					TryGetExport<Docking.DockWorkspace>()?.PruneHistory(node =>
+					AppEnv.AppComposition.TryGetExport<Docking.DockWorkspace>()?.PruneHistory(node =>
 						node.AncestorsAndSelf()
 							.OfType<AssemblyTreeNode>()
 							.Any(a => removed.Contains(a.LoadedAssembly)));
@@ -1092,7 +1085,7 @@ namespace ILSpy.AssemblyTree
 		/// (e.g. the ones <see cref="LoadDependenciesAsync"/> just resolved).
 		/// </summary>
 		public void RefreshDecompiledView()
-			=> TryGetExport<Docking.DockWorkspace>()?.ForceRefreshActiveTab();
+			=> AppEnv.AppComposition.TryGetExport<Docking.DockWorkspace>()?.ForceRefreshActiveTab();
 
 		/// <summary>
 		/// Resolves every assembly reference of each supplied assembly node through that
@@ -1154,7 +1147,7 @@ namespace ILSpy.AssemblyTree
 			// SelectedItem setter early-outs, and DockWorkspace.ShowSelectedNode's
 			// dedup short-circuits — leaving stale decompiled text. Force a fresh
 			// render. Mirrors WPF's RefreshDecompiledView() call.
-			TryGetExport<Docking.DockWorkspace>()?.ForceRefreshActiveTab();
+			AppEnv.AppComposition.TryGetExport<Docking.DockWorkspace>()?.ForceRefreshActiveTab();
 		}
 	}
 }

ILSpy/Commands/CompareContextMenuEntry.cs

@@ -51,7 +51,7 @@ namespace ILSpy.Commands
 				[AssemblyTreeNode left, AssemblyTreeNode right])
 				return;
 
-			var dockWorkspace = TryGetExport<DockWorkspace>();
+			var dockWorkspace = AppComposition.TryGetExport<DockWorkspace>();
 			if (dockWorkspace == null)
 				return;
 			var pane = new CompareTabPageModel(left.LoadedAssembly, right.LoadedAssembly);
@@ -61,12 +61,5 @@ namespace ILSpy.Commands
 			// view is a pair, not a single-node decompile result.
 			dockWorkspace.OpenNewTab(pane);
 		}
-
-		static T? TryGetExport<T>() where T : class
-		{
-			try
-			{ return AppComposition.Current.GetExport<T>(); }
-			catch { return null; }
-		}
 	}
 }

ILSpy/Docking/DockWorkspace.cs

@@ -673,16 +673,7 @@ namespace ILSpy.Docking
 		}
 
 		static IEnumerable<Commands.IProtocolHandler> TryGetProtocolHandlers()
-		{
-			try
-			{
-				return AppEnv.AppComposition.Current.GetExports<Commands.IProtocolHandler>();
-			}
-			catch
-			{
-				return System.Array.Empty<Commands.IProtocolHandler>();
-			}
-		}
+			=> AppEnv.AppComposition.TryGetExports<Commands.IProtocolHandler>();
 
 		// Long-lived decompiler viewmodel — kept alive across metadata interludes so going
 		// back to text doesn't lose the previous decompile until a fresh one supersedes it.
@@ -1133,17 +1124,9 @@ namespace ILSpy.Docking
 			// code-behind subscribes to FocusRequested and posts the focus shift onto the
 			// dispatcher so the freshly-active pane has a frame to surface in the layout
 			// first. Resolving the pane through AppComposition (instead of injecting it)
-			// keeps the dock-workspace decoupled from the search namespace.
-			try
-			{
-				var search = AppEnv.AppComposition.Current.GetExport<ILSpy.Search.SearchPaneModel>();
-				search.RequestFocus();
-			}
-			catch
-			{
-				// Composition isn't available in design-time previews / minimal tests; the
-				// activation alone is enough to be useful there.
-			}
+			// keeps the dock-workspace decoupled from the search namespace. TryGetExport is
+			// null in design-time previews / minimal tests, where the activation alone suffices.
+			AppEnv.AppComposition.TryGetExport<ILSpy.Search.SearchPaneModel>()?.RequestFocus();
 		}
 
 		public ContentTabPage OpenNewTab(ContentPageModel content, SharpTreeNode? sourceNode = null)

ILSpy/Languages/CSharpLanguage.cs

@@ -627,19 +627,10 @@ namespace ILSpy.Languages
 			}
 
 			static IReadOnlyList<IResourceFileHandler> TryDiscoverHandlers()
-			{
-				try
-				{
-					return AppEnv.AppComposition.Current.GetExports<IResourceFileHandler>().ToArray();
-				}
-				catch
-				{
-					// Composition isn't available in tests that bypass the host (e.g. invoking
-					// DecompileAsProject directly with a self-built LoadedAssembly). Fall back
-					// to the raw-bytes behaviour from the base class.
-					return System.Array.Empty<IResourceFileHandler>();
-				}
-			}
+				// Composition isn't available in tests that bypass the host (e.g. invoking
+				// DecompileAsProject directly with a self-built LoadedAssembly); TryGetExports then
+				// yields nothing, falling back to the raw-bytes behaviour from the base class.
+				=> AppEnv.AppComposition.TryGetExports<IResourceFileHandler>().ToArray();
 		}
 
 		static List<EntityHandle> CollectFieldsAndCtors(ITypeDefinition type, bool isStatic)
@@ -820,17 +811,11 @@ namespace ILSpy.Languages
 
 		static bool HasReferenceErrors(MetadataFile module)
 		{
-			try
-			{
-				var atm = AppEnv.AppComposition.Current.GetExport<AssemblyTree.AssemblyTreeModel>();
-				var loadedAssembly = atm.AssemblyList?.GetAssemblies()
-					.FirstOrDefault(la => la.GetMetadataFileOrNull() == module);
-				return loadedAssembly?.LoadedAssemblyReferencesInfo.HasErrors == true;
-			}
-			catch
-			{
-				return false;
-			}
+			// No AssemblyTreeModel without a composition host (tests / minimal hosts) -> no errors.
+			var atm = AppEnv.AppComposition.TryGetExport<AssemblyTree.AssemblyTreeModel>();
+			var loadedAssembly = atm?.AssemblyList?.GetAssemblies()
+				.FirstOrDefault(la => la.GetMetadataFileOrNull() == module);
+			return loadedAssembly?.LoadedAssemblyReferencesInfo.HasErrors == true;
 		}
 	}
 }

ILSpy/Languages/ILAstLanguage.cs

@@ -130,17 +130,6 @@ namespace ILSpy.Languages
 			this.transforms = CSharpDecompiler.GetILTransforms();
 		}
 
-		// DockWorkspace is resolved lazily — taking it as an [ImportingConstructor] argument
-		// creates a composition cycle (DockWorkspace already imports LanguageService, which
-		// imports the registered Languages). Lazy lookup at decompile time breaks the cycle
-		// and Costs only one MEF GetExport call per "Show Steps" button click.
-		DockWorkspace? TryGetDockWorkspace()
-		{
-			try
-			{ return AppComposition.Current.GetExport<DockWorkspace>(); }
-			catch { return null; }
-		}
-
 		public override void DecompileMethod(IMethod method, ITextOutput output, DecompilationOptions options)
 		{
 			base.DecompileMethod(method, output, options);
@@ -188,8 +177,11 @@ namespace ILSpy.Languages
 					OnStepperUpdated();
 				}
 			}
+			// DockWorkspace is resolved lazily here, not via [ImportingConstructor]: it imports
+			// LanguageService, which imports the registered Languages, so a constructor import would
+			// form a composition cycle. The lazy lookup costs one MEF resolve per "Show Steps" click.
 			(output as ISmartTextOutput)?.AddButton(Images.Images.ViewCode, "Show Steps", delegate {
-				TryGetDockWorkspace()?.ShowToolPane(DebugStepsPaneModel.PaneContentId);
+				AppComposition.TryGetExport<DockWorkspace>()?.ShowToolPane(DebugStepsPaneModel.PaneContentId);
 			});
 			output.WriteLine();
 			il.WriteTo(output, DebugStepsPaneModel.WritingOptions);

ILSpy/TextView/DecompilerTabPageModel.cs

@@ -278,14 +278,7 @@ namespace ILSpy.TextView
 		// still construct cleanly.
 		TaskbarProgressService? taskbarProgress;
 		TaskbarProgressService? TaskbarProgress
-			=> taskbarProgress ??= TryGetExport<TaskbarProgressService>();
-
-		static T? TryGetExport<T>() where T : class
-		{
-			try
-			{ return AppEnv.AppComposition.Current.GetExport<T>(); }
-			catch { return null; }
-		}
+			=> taskbarProgress ??= AppEnv.AppComposition.TryGetExport<TaskbarProgressService>();
 
 		public DecompilerTabPageModel()
 		{
@@ -358,16 +351,12 @@ namespace ILSpy.TextView
 		{
 			if (CurrentNode is not { } node)
 				return;
-			try
-			{
-				var languageService = AppEnv.AppComposition.Current.GetExport<Languages.LanguageService>();
-				var dockWorkspace = AppEnv.AppComposition.Current.GetExport<Docking.DockWorkspace>();
-				ILSpy.Commands.SaveCodeHelper.SaveNodeAsync(node, languageService, dockWorkspace).HandleExceptions();
-			}
-			catch
-			{
-				// Best-effort: no save path available (minimal host).
-			}
+			// Best-effort: no save path available without a composition host (minimal/design-time host).
+			var languageService = AppEnv.AppComposition.TryGetExport<Languages.LanguageService>();
+			var dockWorkspace = AppEnv.AppComposition.TryGetExport<Docking.DockWorkspace>();
+			if (languageService is null || dockWorkspace is null)
+				return;
+			ILSpy.Commands.SaveCodeHelper.SaveNodeAsync(node, languageService, dockWorkspace).HandleExceptions();
 		}
 
 		// Fire-and-forget wrapper around DecompileAsync that observes the resulting Task.
@@ -653,35 +642,23 @@ namespace ILSpy.TextView
 		// Pulls the live DecompilerSettings via MEF and returns a clone for this run. Also
 		// bakes the active LanguageService.CurrentVersion into the clone — without this the
 		// toolbar's Language-Version dropdown writes-through to LanguageSettings but never
-		// reaches the decompiler. MEF resolves are wrapped in try/catch so design-time /
-		// minimal test hosts that bypass composition fall back to default settings rather
-		// than throwing.
+		// reaches the decompiler. Resolves go through TryGetExport so design-time / minimal test
+		// hosts that bypass composition fall back to default settings rather than throwing.
 		static ICSharpCode.Decompiler.DecompilerSettings? TryGetLiveDecompilerSettings()
 		{
-			try
-			{
-				var settingsService = AppEnv.AppComposition.Current.GetExport<SettingsService>();
-				var settings = settingsService.DecompilerSettings.Clone();
-				ApplyDisplaySettings(settings, settingsService.DisplaySettings);
-				try
-				{
-					var version = AppEnv.AppComposition.Current.GetExport<Languages.LanguageService>().CurrentVersion;
-					if (Enum.TryParse<ICSharpCode.Decompiler.CSharp.LanguageVersion>(version?.Version, out var languageVersion))
-						settings.SetLanguageVersion(languageVersion);
-					else
-						settings.SetLanguageVersion(ICSharpCode.Decompiler.CSharp.LanguageVersion.Latest);
-				}
-				catch
-				{
-					// No LanguageService available (non-C# language or minimal host) — leave the
-					// settings at whatever default the source DecompilerSettings carried.
-				}
-				return settings;
-			}
-			catch
-			{
+			var settingsService = AppEnv.AppComposition.TryGetExport<SettingsService>();
+			if (settingsService is null)
 				return null;
-			}
+			var settings = settingsService.DecompilerSettings.Clone();
+			ApplyDisplaySettings(settings, settingsService.DisplaySettings);
+			// No LanguageService (non-C# language or minimal host) leaves version null, so the
+			// language version falls back to Latest below.
+			var version = AppEnv.AppComposition.TryGetExport<Languages.LanguageService>()?.CurrentVersion;
+			if (Enum.TryParse<ICSharpCode.Decompiler.CSharp.LanguageVersion>(version?.Version, out var languageVersion))
+				settings.SetLanguageVersion(languageVersion);
+			else
+				settings.SetLanguageVersion(ICSharpCode.Decompiler.CSharp.LanguageVersion.Latest);
+			return settings;
 		}
 
 		/// <summary>

ILSpy/Themes/DocumentSwitcherDropdownBehavior.cs

@@ -69,7 +69,7 @@ namespace ILSpy.Themes
 			if (e.NewValue is not true)
 				return;
 
-			var settings = TryGetSessionSettings();
+			var settings = AppComposition.TryGetExport<SettingsService>()?.SessionSettings;
 			if (settings is not null)
 			{
 				System.ComponentModel.PropertyChangedEventHandler handler = (_, args) => {
@@ -138,7 +138,8 @@ namespace ILSpy.Themes
 			DockPanel.SetDock(button, Avalonia.Controls.Dock.Right);
 			dockPanel.Children.Insert(0, button);
 
-			UpdateVisibility(strip, TryGetSessionSettings()?.MultiLineDocumentTabs ?? false);
+			UpdateVisibility(strip,
+				AppComposition.TryGetExport<SettingsService>()?.SessionSettings?.MultiLineDocumentTabs ?? false);
 		}
 
 		static void PopulateMenu(DocumentTabStrip strip, ContextMenu menu)
@@ -166,14 +167,5 @@ namespace ILSpy.Themes
 		static Button? FindButton(DocumentTabStrip strip)
 			=> strip.GetVisualDescendants().OfType<Button>()
 				.FirstOrDefault(b => (b.Tag as string) == DropdownTag);
-
-		static SettingsService? TryGetSettingsService()
-		{
-			try
-			{ return AppComposition.Current.GetExport<SettingsService>(); }
-			catch { return null; }
-		}
-
-		static SessionSettings? TryGetSessionSettings() => TryGetSettingsService()?.SessionSettings;
 	}
 }

ILSpy/Themes/MultiRowTabStripBehavior.cs

@@ -71,7 +71,7 @@ namespace ILSpy.Themes
 			strip.AddHandler(InputElement.PointerWheelChangedEvent, OnPointerWheel,
 				RoutingStrategies.Tunnel);
 
-			var settings = TryGetSessionSettings();
+			var settings = AppComposition.TryGetExport<SettingsService>()?.SessionSettings;
 			PropertyChangedEventHandler? settingsHandler = null;
 			if (settings is not null)
 			{
@@ -92,7 +92,7 @@ namespace ILSpy.Themes
 
 		static void OnPointerWheel(object? sender, PointerWheelEventArgs e)
 		{
-			var settings = TryGetSessionSettings();
+			var settings = AppComposition.TryGetExport<SettingsService>()?.SessionSettings;
 			if (settings is null || e.Delta.Y == 0 || !settings.MouseWheelTogglesTabStripRows)
 				return;
 			// Idempotent set: rolling further in the same direction keeps the same mode rather than
@@ -125,13 +125,7 @@ namespace ILSpy.Themes
 			}
 		}
 
-		static bool CurrentMultiLine() => TryGetSessionSettings()?.MultiLineDocumentTabs ?? false;
-
-		static SessionSettings? TryGetSessionSettings()
-		{
-			try
-			{ return AppComposition.Current.GetExport<SettingsService>().SessionSettings; }
-			catch { return null; }
-		}
+		static bool CurrentMultiLine()
+			=> AppComposition.TryGetExport<SettingsService>()?.SessionSettings?.MultiLineDocumentTabs ?? false;
 	}
 }

ILSpy/Themes/PreviewTabContextMenuBehavior.cs

@@ -106,7 +106,7 @@ namespace ILSpy.Themes
 				Header = "Freeze tab",
 				IsVisible = tab.IsPreview,
 			};
-			freezeItem.Click += (_, _) => TryGetDockWorkspace()?.FreezeCurrentTab();
+			freezeItem.Click += (_, _) => AppComposition.TryGetExport<DockWorkspace>()?.FreezeCurrentTab();
 
 			// Keep the Freeze entry (and its separator) in sync with IsPreview so they hide once the
 			// tab is frozen (freeze is one-way — there's no matching unfreeze entry).
@@ -131,12 +131,5 @@ namespace ILSpy.Themes
 				},
 			};
 		}
-
-		static DockWorkspace? TryGetDockWorkspace()
-		{
-			try
-			{ return AppComposition.Current.GetExport<DockWorkspace>(); }
-			catch { return null; }
-		}
 	}
 }

ILSpy/Themes/PreviewTabFreezeButtonBehavior.cs

@@ -170,7 +170,7 @@ namespace ILSpy.Themes
 				Mode = BindingMode.OneWay,
 			});
 
-			freezeButton.Click += (_, _) => TryGetDockWorkspace()?.FreezeCurrentTab();
+			freezeButton.Click += (_, _) => AppComposition.TryGetExport<DockWorkspace>()?.FreezeCurrentTab();
 
 			// Insert a new Auto-sized column right before the last (close) column, bump any
 			// existing children at or past that index by +1, and dock the freeze button there.
@@ -186,12 +186,5 @@ namespace ILSpy.Themes
 			Grid.SetColumn(freezeButton, newColIndex);
 			grid.Children.Add(freezeButton);
 		}
-
-		static DockWorkspace? TryGetDockWorkspace()
-		{
-			try
-			{ return AppComposition.Current.GetExport<DockWorkspace>(); }
-			catch { return null; }
-		}
 	}
 }

ILSpy/ViewModels/ContentTabPage.cs

@@ -119,25 +119,13 @@ namespace ILSpy.ViewModels
 		// Document tab context-menu commands (bound from the DocumentTabStripItem in App.axaml,
 		// whose DataContext is this tab). The DockWorkspace owns the dock, so resolve it from the
 		// composition container rather than threading a reference through every tab creation site.
-		static DockWorkspace? Workspace()
-		{
-			try
-			{
-				return ILSpy.AppEnv.AppComposition.Current.GetExport<DockWorkspace>();
-			}
-			catch
-			{
-				return null;
-			}
-		}
-
 		[CommunityToolkit.Mvvm.Input.RelayCommand]
-		private void Close() => Workspace()?.CloseTab(this);
+		private void Close() => ILSpy.AppEnv.AppComposition.TryGetExport<DockWorkspace>()?.CloseTab(this);
 
 		[CommunityToolkit.Mvvm.Input.RelayCommand]
-		private void CloseAllButThis() => Workspace()?.CloseAllTabsExcept(this);
+		private void CloseAllButThis() => ILSpy.AppEnv.AppComposition.TryGetExport<DockWorkspace>()?.CloseAllTabsExcept(this);
 
 		[CommunityToolkit.Mvvm.Input.RelayCommand]
-		private void CloseAll() => Workspace()?.CloseAllTabs();
+		private void CloseAll() => ILSpy.AppEnv.AppComposition.TryGetExport<DockWorkspace>()?.CloseAllTabs();
 	}
 }

ILSpy/ViewModels/DebugStepsPaneModel.cs

@@ -205,17 +205,9 @@ namespace ILSpy.ViewModels
 		void RequestRedecompile(int stepLimit, bool isDebug)
 		{
 			lastSelectedStep = stepLimit;
-			DockWorkspace? dock;
-			try
-			{
-				dock = AppComposition.Current.GetExport<DockWorkspace>();
-			}
-			catch
-			{
-				// Composition unavailable in design-time previews; the gesture is a no-op there.
-				return;
-			}
-			dock.ActiveDecompilerTab?.RestartDecompileWithStepLimit(stepLimit, isDebug);
+			// Composition unavailable in design-time previews; the gesture is a no-op there.
+			var dock = AppComposition.TryGetExport<DockWorkspace>();
+			dock?.ActiveDecompilerTab?.RestartDecompileWithStepLimit(stepLimit, isDebug);
 		}
 	}
 }