[xabt] Add HasMetadata checks to all PEReader code paths to skip native Windows DLLs (#10938)

Context: #10862

## Summary

Extracted from PR #10862: Add `PEReader.HasMetadata` checks before calling `GetMetadataReader()` across all code paths that use `PEReader` to prevent exceptions when processing native (non-.NET) PE DLLs.

## Problem

When NuGet packages (like MSTest) include native Windows `.dll` files that flow into `ResolvedFileToPublish`, calling `PEReader.GetMetadataReader()` on these files throws an exception because they are not .NET assemblies and have no CLI metadata.

## Fix

Added `PEReader.HasMetadata` guards before `GetMetadataReader()` calls across all relevant code paths. In MSBuild tasks with log access, a `LogDebugMessage()` call is included when skipping non-.NET assemblies.

Co-authored-by: jonathanpeppers <840039+jonathanpeppers@users.noreply.github.com>

Author: Copilot

src/Xamarin.Android.Build.Tasks/Tasks/CheckForInvalidDesignerConfig.cs

@@ -39,6 +39,9 @@ static bool HasResourceDesignerAssemblyReference (ITaskItem assembly)
 				return false;
 			}
 			using var pe = new PEReader (File.OpenRead (assembly.ItemSpec));
+			if (!pe.HasMetadata) {
+				return false;
+			}
 			var reader = pe.GetMetadataReader ();
 			return HasResourceDesignerAssemblyReference (reader);
 		}

src/Xamarin.Android.Build.Tasks/Tasks/FilterAssemblies.cs

@@ -57,6 +57,10 @@ public override bool RunTask ()
 		void ProcessAssembly(ITaskItem assemblyItem, List<ITaskItem> output)
 		{
 			using var pe = new PEReader (File.OpenRead (assemblyItem.ItemSpec));
+			if (!pe.HasMetadata) {
+				Log.LogDebugMessage ($"Skipping non-.NET assembly: {assemblyItem.ItemSpec}");
+				return;
+			}
 			var reader = pe.GetMetadataReader ();
 			// Check in-memory cache
 			var module = reader.GetModuleDefinition ();

src/Xamarin.Android.Build.Tasks/Tasks/ResolveLibraryProjectImports.cs

@@ -256,6 +256,10 @@ void Extract (
 				Log.LogDebugMessage ($"Refreshing {fileName}");
 
 				using (var pe = new PEReader (File.OpenRead (assemblyPath))) {
+					if (!pe.HasMetadata) {
+						Log.LogDebugMessage ($"Skipping non-.NET assembly: {assemblyPath}");
+						continue;
+					}
 					var reader = pe.GetMetadataReader ();
 					foreach (var handle in reader.ManifestResources) {
 						var resource = reader.GetManifestResource (handle);

src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/Tasks/FilterAssembliesTests.cs

@@ -100,5 +100,78 @@ public async Task GuavaListenableFuture ()
 			var expected = new [] { "Xamarin.Google.Guava.ListenableFuture.dll" };
 			CollectionAssert.AreEqual (expected, actual);
 		}
+
+		[Test]
+		public void NativeDll_Skipped ()
+		{
+			// Create a minimal valid PE file without CLI metadata (a native DLL)
+			var nativeDll = Path.Combine (tempDirectory, "native.dll");
+			CreateNativePE (nativeDll);
+			var actual = Run (nativeDll);
+			CollectionAssert.IsEmpty (actual, "Native DLLs without CLI metadata should be skipped.");
+		}
+
+		/// <summary>
+		/// Creates a minimal valid PE file without CLI metadata, simulating a native DLL.
+		/// </summary>
+		static void CreateNativePE (string path)
+		{
+			using var fs = File.Create (path);
+			using var writer = new BinaryWriter (fs);
+
+			// DOS header: 'MZ' magic + padding to e_lfanew at offset 0x3C
+			writer.Write ((ushort) 0x5A4D);         // e_magic = 'MZ'
+			writer.Write (new byte [58]);            // pad to offset 0x3C
+			writer.Write ((uint) 0x80);              // e_lfanew = 0x80
+
+			// Pad to PE signature at offset 0x80
+			writer.Write (new byte [0x80 - 0x40]);
+
+			// PE signature: 'PE\0\0'
+			writer.Write ((uint) 0x00004550);
+
+			// COFF header (20 bytes)
+			writer.Write ((ushort) 0x14C);           // Machine = IMAGE_FILE_MACHINE_I386
+			writer.Write ((ushort) 0);               // NumberOfSections = 0
+			writer.Write ((uint) 0);                 // TimeDateStamp
+			writer.Write ((uint) 0);                 // PointerToSymbolTable
+			writer.Write ((uint) 0);                 // NumberOfSymbols
+			writer.Write ((ushort) 0xE0);            // SizeOfOptionalHeader (PE32)
+			writer.Write ((ushort) 0x2102);          // Characteristics = DLL | EXECUTABLE_IMAGE | LARGE_ADDRESS_AWARE
+
+			// Optional header (PE32) — minimal, no CLI header directory entry
+			writer.Write ((ushort) 0x10B);           // Magic = PE32
+			writer.Write ((byte) 0);                 // MajorLinkerVersion
+			writer.Write ((byte) 0);                 // MinorLinkerVersion
+			writer.Write ((uint) 0);                 // SizeOfCode
+			writer.Write ((uint) 0);                 // SizeOfInitializedData
+			writer.Write ((uint) 0);                 // SizeOfUninitializedData
+			writer.Write ((uint) 0);                 // AddressOfEntryPoint
+			writer.Write ((uint) 0);                 // BaseOfCode
+			writer.Write ((uint) 0);                 // BaseOfData
+			writer.Write ((uint) 0x10000);           // ImageBase
+			writer.Write ((uint) 0x1000);            // SectionAlignment
+			writer.Write ((uint) 0x200);             // FileAlignment
+			writer.Write ((ushort) 4);               // MajorOperatingSystemVersion
+			writer.Write ((ushort) 0);               // MinorOperatingSystemVersion
+			writer.Write ((ushort) 0);               // MajorImageVersion
+			writer.Write ((ushort) 0);               // MinorImageVersion
+			writer.Write ((ushort) 4);               // MajorSubsystemVersion
+			writer.Write ((ushort) 0);               // MinorSubsystemVersion
+			writer.Write ((uint) 0);                 // Win32VersionValue
+			writer.Write ((uint) 0x1000);            // SizeOfImage
+			writer.Write ((uint) 0x200);             // SizeOfHeaders
+			writer.Write ((uint) 0);                 // CheckSum
+			writer.Write ((ushort) 3);               // Subsystem = WINDOWS_CUI
+			writer.Write ((ushort) 0);               // DllCharacteristics
+			writer.Write ((uint) 0x100000);          // SizeOfStackReserve
+			writer.Write ((uint) 0x1000);            // SizeOfStackCommit
+			writer.Write ((uint) 0x100000);          // SizeOfHeapReserve
+			writer.Write ((uint) 0x1000);            // SizeOfHeapCommit
+			writer.Write ((uint) 0);                 // LoaderFlags
+			writer.Write ((uint) 16);                // NumberOfRvaAndSizes
+			// Data directories (16 entries × 8 bytes = 128 bytes), all zeroed — no CLI header
+			writer.Write (new byte [128]);
+		}
 	}
 }

src/Xamarin.Android.Build.Tasks/Utilities/MetadataResolver.cs

@@ -19,7 +19,12 @@ public MetadataReader GetAssemblyReader (string assemblyName)
 		{
 			var assemblyPath = Resolve (assemblyName);
 			if (!cache.TryGetValue (assemblyPath, out PEReader reader)) {
-				cache.Add (assemblyPath, reader = new PEReader (File.OpenRead (assemblyPath)));
+				reader = new PEReader (File.OpenRead (assemblyPath));
+				if (!reader.HasMetadata) {
+					reader.Dispose ();
+					throw new InvalidOperationException ($"Assembly '{assemblyPath}' is not a .NET assembly.");
+				}
+				cache.Add (assemblyPath, reader);
 			}
 			return reader.GetMetadataReader ();
 		}

src/Xamarin.Android.Build.Tasks/Utilities/MonoAndroidHelper.cs

@@ -353,6 +353,9 @@ public static bool HasMonoAndroidReference (ITaskItem assembly)
 				return true;
 
 			using var pe = new PEReader (File.OpenRead (assembly.ItemSpec));
+			if (!pe.HasMetadata) {
+				return false; // not a .NET assembly (no CLI metadata)
+			}
 			var reader = pe.GetMetadataReader ();
 			return HasMonoAndroidReference (reader);
 		}
@@ -374,6 +377,10 @@ public static bool IsReferenceAssembly (string assembly, TaskLoggingHelper log)
 		{
 			using (var stream = File.OpenRead (assembly))
 			using (var pe = new PEReader (stream)) {
+				if (!pe.HasMetadata) {
+					log.LogDebugMessage ($"Skipping non-.NET assembly: {assembly}");
+					return false;
+				}
 				var reader = pe.GetMetadataReader ();
 				var assemblyDefinition = reader.GetAssemblyDefinition ();
 				foreach (var handle in assemblyDefinition.GetCustomAttributes ()) {

src/Xamarin.Android.Build.Tasks/Utilities/ResourceDesignerImportGenerator.cs

@@ -44,6 +44,10 @@ public void CreateImportMethods (IEnumerable<ITaskItem> libraries)
 			primary.Members.Add (method);
 			foreach (var assemblyPath in libraries) {
 				using (var pe = new PEReader (File.OpenRead (assemblyPath.ItemSpec))) {
+					if (!pe.HasMetadata) {
+						Log.LogDebugMessage ($"Skipping non-.NET assembly: {assemblyPath.ItemSpec}");
+						continue;
+					}
 					var reader = pe.GetMetadataReader ();
 					var resourceDesignerName = GetResourceDesignerClass (reader);
 					if (string.IsNullOrEmpty (resourceDesignerName)) {