Add support for nested types in the corelib.h parser for rooting descriptors (#105432)

Author: jkoritzinsky

src/coreclr/vm/corelib.h

@@ -1123,15 +1123,10 @@ DEFINE_METHOD(UTF8STRINGMARSHALLER, CONVERT_TO_MANAGED, ConvertToManaged, SM_Ptr
 DEFINE_METHOD(UTF8STRINGMARSHALLER, CONVERT_TO_UNMANAGED, ConvertToUnmanaged, SM_Str_RetPtrByte)
 DEFINE_METHOD(UTF8STRINGMARSHALLER, FREE, Free, SM_PtrByte_RetVoid)
 
-// The generator for the ILLink XML doesn't understand inner classes so generation
-// needs to skip the following type.
-// See https://github.com/dotnet/runtime/issues/71847
-#ifndef FOR_ILLINK
 DEFINE_CLASS(UTF8STRINGMARSHALLER_IN, Marshalling, Utf8StringMarshaller+ManagedToUnmanagedIn)
 DEFINE_METHOD(UTF8STRINGMARSHALLER_IN, FROM_MANAGED, FromManaged, IM_Str_SpanOfByte_RetVoid)
 DEFINE_METHOD(UTF8STRINGMARSHALLER_IN, TO_UNMANAGED, ToUnmanaged, IM_RetPtrByte)
 DEFINE_METHOD(UTF8STRINGMARSHALLER_IN, FREE, Free, IM_RetVoid)
-#endif // FOR_ILLINK
 
 DEFINE_CLASS(UTF8BUFFERMARSHALER, StubHelpers, UTF8BufferMarshaler)
 DEFINE_METHOD(UTF8BUFFERMARSHALER, CONVERT_TO_NATIVE, ConvertToNative, NoSig)
@@ -1180,9 +1175,7 @@ DEFINE_CLASS(EXCEPTIONSERVICES_INTERNALCALLS, ExceptionServices, InternalCalls)
 DEFINE_CLASS(STACKFRAMEITERATOR, Runtime, StackFrameIterator)
 #endif // FEATURE_EH_FUNCLETS
 
-#ifndef FOR_ILLINK
 DEFINE_CLASS(EXINFO, Runtime, EH+ExInfo)
-#endif // FOR_ILLINK
 
 DEFINE_CLASS_U(System, GCMemoryInfoData, GCMemoryInfoData)
 DEFINE_FIELD_U(_highMemoryLoadThresholdBytes, GCMemoryInfoData, highMemLoadThresholdBytes)

src/tools/illink/src/ILLink.Tasks/CreateRuntimeRootDescriptorFile.cs

@@ -471,7 +471,10 @@ string GetFullClassName (string classNamespace, string className)
 				Log.LogError ($"Unknown namespace '{classNamespace}'.");
 			}
 
-			return namespaceDictionary[classNamespace] + "." + className;
+			// Convert from the System.Reflection/CoreCLR nested type name format to the IL/Cecil format.
+			string classNameWithCecilNestedFormat = className.Replace ('+', '/');
+
+			return namespaceDictionary[classNamespace] + "." + classNameWithCecilNestedFormat;
 		}
 
 		void InitializeDefineConstants ()

src/tools/illink/test/ILLink.Tasks.Tests/CreateRuntimeRootDescriptorFileTests.cs

@@ -39,7 +39,9 @@ public void TestCoreLibClassGen ()
 				"#endif // FEATURE_BOTH",
 				"#if FOR_ILLINK",
 				"DEFINE_METHOD(TESTCLASS, TESTMETHODFORILLINK, TestMethodForILLink, 5)",
-				"#endif"
+				"#endif",
+				"DEFINE_CLASS(NESTEDTESTCLASS, TestNS, TestClass+Nested)",
+				"DEFINE_METHOD(NESTEDTESTCLASS, TESTMETHOD, TestMethod, 0)"
 				});
 
 			File.WriteAllText ("namespace.h",
@@ -90,6 +92,8 @@ public void TestCoreLibClassGen ()
 						new XElement ("method", new XAttribute ("name", "TestMethodIfNotBoth")),
 						new XElement ("method", new XAttribute ("name", "TestMethodIfNotBothForILLink")),
 						new XElement ("method", new XAttribute ("name", "TestMethodForILLink"))),
+					new XElement ("type", new XAttribute("fullname", "TestNS.TestClass/Nested"),
+						new XElement ("method", new XAttribute("name", "TestMethod"))),
 					new XElement ("type", new XAttribute ("fullname", "TestNS.TestAlwaysException"),
 						new XElement ("method", new XAttribute ("name", ".ctor"))),
 					new XElement ("type", new XAttribute ("fullname", "TestNS.TestFeatureOnException"),