Show metadata tables when opening a standalone portable PDB

A standalone portable PDB (or raw metadata stream) loads as a metadata-only
MetadataFile, but the tree node was left empty: LoadChildren early-returned for
any kind other than PortableExecutable/WebCIL, so the node showed an expander
over no children. This regressed in the WPF -> Avalonia port, which dropped the
old default switch arm; release/10.1 still populated such nodes with the
metadata table and heap nodes directly. Restore that behavior.

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

ILSpy.Tests/Metadata/StandalonePdbTreeTests.cs

@@ -0,0 +1,73 @@
+// 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.IO;
+using System.Linq;
+using System.Threading.Tasks;
+
+using Avalonia.Headless.NUnit;
+
+using AwesomeAssertions;
+
+using ICSharpCode.ILSpy.Metadata;
+using ICSharpCode.ILSpy.Metadata.DebugTables;
+using ICSharpCode.ILSpy.TreeNodes;
+
+using NUnit.Framework;
+
+namespace ICSharpCode.ILSpy.Tests.Metadata;
+
+[TestFixture]
+public class StandalonePdbTreeTests
+{
+	[AvaloniaTest]
+	public async Task Opening_A_Standalone_Portable_PDB_Surfaces_Its_Metadata_Tables_And_Heaps()
+	{
+		// A standalone .pdb (no companion assembly) loads as a metadata-only MetadataFile of
+		// kind ProgramDebugDatabase. Its tree node must expand to the PDB's metadata tables and
+		// heaps directly under the file node; before the fix the node had an expander but zero
+		// children (the "empty tree" symptom).
+
+		// The test SDK builds this assembly with a sidecar portable PDB, so use that PDB on its
+		// own as the standalone fixture.
+		var pdbPath = Path.ChangeExtension(typeof(StandalonePdbTreeTests).Assembly.Location, ".pdb");
+		File.Exists(pdbPath).Should().BeTrue(
+			$"the test assembly must ship a sidecar portable PDB to use as a standalone fixture (looked for '{pdbPath}')");
+
+		var (_, vm) = await TestHarness.BootAsync();
+
+		var loaded = await vm.OpenAssemblyAsync(pdbPath);
+		TestCapture.Step("opened-standalone-pdb");
+
+		var pdbNode = vm.AssemblyTreeModel.FindNode<AssemblyTreeNode>(loaded.ShortName);
+		pdbNode.EnsureLazyChildren();
+		TestCapture.Step("pdb-node-expanded");
+
+		pdbNode.Children.Should().NotBeEmpty(
+			"a standalone portable PDB must populate its tree node instead of rendering empty");
+
+		var tables = pdbNode.GetChild<MetadataTablesTreeNode>();
+		tables.EnsureLazyChildren();
+		tables.Children.OfType<DocumentTableTreeNode>().Should().NotBeEmpty(
+			"the standalone PDB's Tables subtree must expose the Document table — the lead debug-only table that always has rows in a populated PDB");
+
+		// The heap nodes are also surfaced directly (string/userstring/guid/blob).
+		pdbNode.Children.OfType<StringHeapTreeNode>().Should().ContainSingle();
+		pdbNode.Children.OfType<BlobHeapTreeNode>().Should().ContainSingle();
+	}
+}

ILSpy/TreeNodes/AssemblyTreeNode.cs

@@ -359,6 +359,14 @@ namespace ICSharpCode.ILSpy.TreeNodes
 			if (module.Kind != MetadataFile.MetadataFileKind.PortableExecutable
 				&& module.Kind != MetadataFile.MetadataFileKind.WebCIL)
 			{
+				// Standalone metadata-only files (a portable .pdb, or a raw metadata stream)
+				// are entirely metadata, so surface the tables and heaps directly under the
+				// file node rather than nesting them inside a "Metadata" folder.
+				Children.Add(new ICSharpCode.ILSpy.Metadata.MetadataTablesTreeNode(module));
+				Children.Add(new ICSharpCode.ILSpy.Metadata.StringHeapTreeNode(module));
+				Children.Add(new ICSharpCode.ILSpy.Metadata.UserStringHeapTreeNode(module));
+				Children.Add(new ICSharpCode.ILSpy.Metadata.GuidHeapTreeNode(module));
+				Children.Add(new ICSharpCode.ILSpy.Metadata.BlobHeapTreeNode(module));
 				return;
 			}