Add support for exported types in illink XML formats (#102487)

Addresses the TODO in the native AOT port.

Ran into inability of rooting things from mscorlib with the illink XML format on native AOT so decided to fix the TODO.

(It was possible to work around with `Type.GetType` (that's a supported pattern) or rd.xml, but this should work with the descriptors too.)

Author: MichalStrehovsky

src/coreclr/tools/Common/Compiler/ProcessLinkerXmlBase.cs

@@ -217,9 +217,10 @@ protected virtual void ProcessTypes(ModuleDesc assembly, XPathNavigator nav, boo
                         continue;
                 }
 
-                // TODO: Process exported types
+                MetadataType? type = CecilCompatibleTypeParser.GetType(assembly, fullname);
 
-                TypeDesc? type = CecilCompatibleTypeParser.GetType(assembly, fullname);
+                if (type != null && type.Module != assembly)
+                    type = ProcessExportedType(type, assembly, typeNav);
 
                 if (type == null)
                 {
@@ -234,6 +235,8 @@ protected virtual void ProcessTypes(ModuleDesc assembly, XPathNavigator nav, boo
             }
         }
 
+        protected virtual MetadataType? ProcessExportedType(MetadataType exported, ModuleDesc assembly, XPathNavigator nav) => exported;
+
         private void MatchType(TypeDesc type, Regex regex, XPathNavigator nav)
         {
             StringBuilder sb = new StringBuilder();
@@ -759,7 +762,7 @@ public bool TryConvertValue(string value, TypeDesc type, out object? result)
 
     public class CecilCompatibleTypeParser
     {
-        public static TypeDesc? GetType(ModuleDesc assembly, string fullName)
+        public static MetadataType? GetType(ModuleDesc assembly, string fullName)
         {
             Debug.Assert(!string.IsNullOrEmpty(fullName));
             var position = fullName.IndexOf('/');

src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/BodySubstitutionParser.cs

@@ -40,7 +40,7 @@ protected override void ProcessAssembly(ModuleDesc assembly, XPathNavigator nav,
             ProcessTypes(assembly, nav, warnOnUnresolvedTypes);
         }
 
-        // protected override TypeDesc? ProcessExportedType(ExportedType exported, ModuleDesc assembly, XPathNavigator nav) => null;
+        protected override MetadataType ProcessExportedType(MetadataType exported, ModuleDesc assembly, XPathNavigator nav) => null;
 
         protected override bool ProcessTypePattern(string fullname, ModuleDesc assembly, XPathNavigator nav) => false;
 

src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/DescriptorMarker.cs

@@ -162,6 +162,14 @@ private void MarkAndPreserve(TypeDesc type, XPathNavigator nav, TypePreserve pre
         }
 #endif
 
+        protected override MetadataType? ProcessExportedType(MetadataType exported, ModuleDesc assembly, XPathNavigator nav)
+        {
+            // Rooting module metadata roots type forwarder metadata for all types in the module that are reflection visible.
+            // (We don't track individual type forwarders right now.)
+            _dependencies.Add(_factory.ModuleMetadata(assembly), "Type used through forwarder");
+            return base.ProcessExportedType(exported, assembly, nav);
+        }
+
         protected override void ProcessType(TypeDesc type, XPathNavigator nav)
         {
             Debug.Assert(ShouldProcessElement(nav));

src/tests/nativeaot/SmokeTests/TrimmingBehaviors/ILLinkDescriptor.cs

@@ -17,6 +17,7 @@ public static int Run()
         ThrowIfMemberNotPresent(typeof(ILLinkDescriptor), nameof(PropertyKeptViaDescriptor));
         ThrowIfMemberNotPresent(typeof(ILLinkDescriptor), nameof(EventKeptViaDescriptor));
         ThrowIfTypeNotPresent(typeof(ILLinkDescriptor), nameof(NestedTypeKeptViaDescriptor));
+        ThrowIfTypeNotPresent("LibraryClass, ShimLibrary");
         ThrowIfTypePresent(typeof(ILLinkDescriptor), nameof(NestedTypeNonKept));
         return 100;
     }
@@ -51,6 +52,10 @@ class NestedTypeNonKept
         Justification = "That's the point")]
     private static bool IsTypePresent(Type testType, string typeName) => testType.GetNestedType(typeName, BindingFlags.NonPublic | BindingFlags.Public) != null;
 
+    [UnconditionalSuppressMessage("ReflectionAnalysis", "IL2057:UnrecognizedReflectionPattern",
+        Justification = "That's the point")]
+    private static bool IsTypePresent(string typeName) => Type.GetType(typeName) != null;
+
     [UnconditionalSuppressMessage("ReflectionAnalysis", "IL2070:UnrecognizedReflectionPattern",
         Justification = "That's the point")]
     private static bool IsMemberPresent(Type testType, string memberName) {
@@ -70,6 +75,14 @@ private static void ThrowIfTypeNotPresent(Type testType, string typeName)
         }
     }
 
+    private static void ThrowIfTypeNotPresent(string typeName)
+    {
+        if (!IsTypePresent(typeName))
+        {
+            throw new Exception(typeName);
+        }
+    }
+
     private static void ThrowIfTypePresent(Type testType, string typeName)
     {
         if (IsTypePresent(testType, typeName))

src/tests/nativeaot/SmokeTests/TrimmingBehaviors/Library.cs

@@ -0,0 +1,4 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+public class LibraryClass { }

src/tests/nativeaot/SmokeTests/TrimmingBehaviors/Library.csproj

@@ -0,0 +1,8 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <OutputType>Library</OutputType>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="Library.cs" />
+  </ItemGroup>
+</Project>

src/tests/nativeaot/SmokeTests/TrimmingBehaviors/NonEmbedded.ILLink.Descriptor.xml

@@ -4,4 +4,8 @@
       <method name="methodKeptViaStandaloneDescriptor"/>
     </type>
   </assembly>
+
+  <assembly fullname="ShimLibrary">
+    <type fullname="LibraryClass" />
+  </assembly>
 </linker>

src/tests/nativeaot/SmokeTests/TrimmingBehaviors/ShimLibrary.cs

@@ -0,0 +1,6 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Runtime.CompilerServices;
+
+[assembly: TypeForwardedTo(typeof(LibraryClass))]

src/tests/nativeaot/SmokeTests/TrimmingBehaviors/ShimLibrary.csproj

@@ -0,0 +1,11 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <OutputType>Library</OutputType>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="ShimLibrary.cs" />
+  </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="Library.csproj" />
+  </ItemGroup>
+</Project>

src/tests/nativeaot/SmokeTests/TrimmingBehaviors/TrimmingBehaviors.csproj

@@ -8,6 +8,11 @@
     <!-- We don't run the scanner in optimized builds -->
     <CLRTestTargetUnsupported Condition="'$(IlcMultiModule)' == 'true'">true</CLRTestTargetUnsupported>
   </PropertyGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="ShimLibrary.csproj" />
+  </ItemGroup>
+
   <ItemGroup>
     <Compile Include="Dataflow.cs" />
     <Compile Include="DeadCodeElimination.cs" />