Open from GAC dialog — Windows-only, mirrors WPF gating

Replaces the NotImplementedDialog stub in OpenFromGacCommand with a real
dialog. CanExecute gates on OperatingSystem.IsWindows() since the Windows
Global Assembly Cache doesn't exist on Linux/macOS (matches WPF's
AppEnvironment.IsWindows gate). The actual GAC enumeration uses the shared
UniversalAssemblyResolver.EnumerateGac() + GetAssemblyInGac() pair from
ICSharpCode.Decompiler — no platform-specific code in the Avalonia tree.

Assisted-by: Claude:claude-opus-4-7:Claude Code

ILSpy/Commands/FileCommands.cs

@@ -89,7 +89,39 @@ namespace ILSpy.Commands
 	[Shared]
 	sealed class OpenFromGacCommand : SimpleCommand
 	{
-		public override void Execute(object? parameter) => NotImplementedDialog.Show(Resources.OpenFrom_GAC);
+		readonly AssemblyTreeModel assemblyTreeModel;
+
+		[ImportingConstructor]
+		public OpenFromGacCommand(AssemblyTreeModel assemblyTreeModel)
+		{
+			this.assemblyTreeModel = assemblyTreeModel;
+		}
+
+		// The Windows GAC doesn't exist on Linux/macOS. WPF gates this command on
+		// `AppEnvironment.IsWindows`; Avalonia uses the BCL runtime check that already
+		// returns the right answer per OS.
+		public override bool CanExecute(object? parameter) => System.OperatingSystem.IsWindows();
+
+		public override void Execute(object? parameter)
+		{
+			if (!CanExecute(parameter))
+				return;
+			var owner = (global::Avalonia.Application.Current?.ApplicationLifetime
+				as global::Avalonia.Controls.ApplicationLifetimes.IClassicDesktopStyleApplicationLifetime)?.MainWindow;
+			if (owner == null)
+				return;
+			_ = ShowAsync(owner);
+		}
+
+		async System.Threading.Tasks.Task ShowAsync(global::Avalonia.Controls.Window owner)
+		{
+			var dlg = new Views.OpenFromGacDialog();
+			var fileNames = await dlg.ShowDialog<string[]>(owner);
+			if (fileNames == null || fileNames.Length == 0)
+				return;
+			foreach (var name in fileNames)
+				assemblyTreeModel.AssemblyList?.OpenAssembly(name);
+		}
 	}
 
 	[ExportMainMenuCommand(ParentMenuID = nameof(Resources._File), Header = nameof(Resources.ManageAssembly_Lists), MenuIcon = "Images/AssemblyList", MenuCategory = nameof(Resources.Open), MenuOrder = 1.7)]

ILSpy/Views/OpenFromGacDialog.axaml

@@ -0,0 +1,25 @@
+<Window xmlns="https://github.com/avaloniaui"
+        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+        x:Class="ILSpy.Views.OpenFromGacDialog"
+        Width="600" Height="450" MinWidth="500" MinHeight="300"
+        WindowStartupLocation="CenterOwner"
+        Title="Open from GAC">
+	<Grid Margin="12,8" RowDefinitions="Auto,*,Auto,Auto" RowSpacing="6">
+		<Grid Grid.Row="0" ColumnDefinitions="Auto,*">
+			<TextBlock Grid.Column="0" Text="Filter:" VerticalAlignment="Center" Margin="0,0,8,0" />
+			<TextBox Grid.Column="1" Name="FilterBox" />
+		</Grid>
+		<ListBox Grid.Row="1" Name="EntriesList" SelectionMode="Multiple">
+			<ListBox.ItemTemplate>
+				<DataTemplate>
+					<TextBlock Text="{Binding}" />
+				</DataTemplate>
+			</ListBox.ItemTemplate>
+		</ListBox>
+		<ProgressBar Grid.Row="2" Name="LoadingBar" Height="6" IsIndeterminate="True" />
+		<StackPanel Grid.Row="3" Orientation="Horizontal" HorizontalAlignment="Right" Spacing="6">
+			<Button Name="OkButton" Content="Open" IsDefault="True" IsEnabled="False" MinWidth="72" />
+			<Button Name="CancelButton" Content="Cancel" IsCancel="True" MinWidth="72" />
+		</StackPanel>
+	</Grid>
+</Window>

ILSpy/Views/OpenFromGacDialog.axaml.cs

@@ -0,0 +1,149 @@
+// Copyright (c) 2026 AlphaSierraPapa for the SharpDevelop Team
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy of this
+// software and associated documentation files (the "Software"), to deal in the Software
+// without restriction, including without limitation the rights to use, copy, modify, merge,
+// publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons
+// to whom the Software is furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all copies or
+// substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
+// INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
+// PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE
+// FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
+// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+// DEALINGS IN THE SOFTWARE.
+
+using System;
+using System.Collections.Generic;
+using System.Collections.ObjectModel;
+using System.Linq;
+using System.Threading.Tasks;
+
+using Avalonia.Controls;
+using Avalonia.Markup.Xaml;
+using Avalonia.Threading;
+
+using ICSharpCode.Decompiler.Metadata;
+
+namespace ILSpy.Views
+{
+	/// <summary>
+	/// "Open from GAC" dialog: enumerates the Global Assembly Cache via the shared
+	/// <see cref="UniversalAssemblyResolver.EnumerateGac"/> + <see cref="UniversalAssemblyResolver.GetAssemblyInGac"/>
+	/// pair, surfaces the assemblies in a filterable list, returns the selected
+	/// absolute file paths. Windows-only — the GAC doesn't exist on Linux/macOS, and
+	/// the command's CanExecute gates on <c>OperatingSystem.IsWindows()</c>.
+	/// </summary>
+	public partial class OpenFromGacDialog : Window
+	{
+		readonly ObservableCollection<GacEntry> allEntries = new();
+		readonly ObservableCollection<GacEntry> filteredEntries = new();
+		readonly System.Threading.CancellationTokenSource fetchCts = new();
+
+		ListBox entriesList = null!;
+		TextBox filterBox = null!;
+		ProgressBar loadingBar = null!;
+		Button okButton = null!;
+
+		public OpenFromGacDialog()
+		{
+			InitializeComponent();
+			entriesList = this.FindControl<ListBox>("EntriesList")!;
+			filterBox = this.FindControl<TextBox>("FilterBox")!;
+			loadingBar = this.FindControl<ProgressBar>("LoadingBar")!;
+			okButton = this.FindControl<Button>("OkButton")!;
+			entriesList.ItemsSource = filteredEntries;
+			entriesList.SelectionChanged += (_, _) => okButton.IsEnabled = entriesList.SelectedItems!.Count > 0;
+			filterBox.TextChanged += (_, _) => Refilter();
+			okButton.Click += (_, _) => Close(SelectedFileNames);
+			this.FindControl<Button>("CancelButton")!.Click += (_, _) => Close(System.Array.Empty<string>());
+			Closed += (_, _) => fetchCts.Cancel();
+			_ = FetchAsync();
+		}
+
+		void InitializeComponent() => AvaloniaXamlLoader.Load(this);
+
+		public string[] SelectedFileNames
+			=> entriesList.SelectedItems!.OfType<GacEntry>().Select(e => e.FileName).ToArray();
+
+		async Task FetchAsync()
+		{
+			var token = fetchCts.Token;
+			var seen = new HashSet<string>();
+			try
+			{
+				await Task.Run(() => {
+					foreach (var reference in UniversalAssemblyResolver.EnumerateGac())
+					{
+						if (token.IsCancellationRequested)
+							return;
+						if (!seen.Add(reference.FullName))
+							continue;
+						var path = UniversalAssemblyResolver.GetAssemblyInGac(reference);
+						if (path == null)
+							continue;
+						var entry = new GacEntry(reference, path);
+						Dispatcher.UIThread.Post(() => AddEntry(entry));
+					}
+				}, token);
+			}
+			catch (OperationCanceledException)
+			{
+				// Window closed before the enumeration finished — nothing to do.
+			}
+			finally
+			{
+				loadingBar.IsVisible = false;
+			}
+		}
+
+		void AddEntry(GacEntry entry)
+		{
+			allEntries.Add(entry);
+			if (PassesFilter(entry))
+				filteredEntries.Add(entry);
+		}
+
+		void Refilter()
+		{
+			filteredEntries.Clear();
+			foreach (var entry in allEntries.Where(PassesFilter))
+				filteredEntries.Add(entry);
+		}
+
+		bool PassesFilter(GacEntry entry)
+		{
+			var text = filterBox.Text?.Trim();
+			if (string.IsNullOrEmpty(text))
+				return true;
+			var label = entry.ToString();
+			foreach (var token in text.Split(' ', System.StringSplitOptions.RemoveEmptyEntries))
+			{
+				if (label.IndexOf(token, System.StringComparison.OrdinalIgnoreCase) < 0)
+					return false;
+			}
+			return true;
+		}
+
+		sealed class GacEntry(AssemblyNameReference reference, string fileName)
+		{
+			public string FileName { get; } = fileName;
+			public override string ToString()
+				=> $"{reference.Name}, Version={reference.Version}, Culture={(reference.Culture is { Length: > 0 } c ? c : "neutral")}, PublicKeyToken={FormatPublicKey(reference)}";
+
+			static string FormatPublicKey(AssemblyNameReference reference)
+			{
+				var token = reference.PublicKeyToken;
+				if (token == null || token.Length == 0)
+					return "null";
+				var sb = new System.Text.StringBuilder(token.Length * 2);
+				foreach (var b in token)
+					sb.AppendFormat("{0:x2}", b);
+				return sb.ToString();
+			}
+		}
+	}
+}