From f97890c1c5491bbd72e7a61e54b8a3e6ee1ff0e3 Mon Sep 17 00:00:00 2001
From: David Wrighton <davidwr@microsoft.com>
Date: Wed, 15 Jan 2025 16:45:30 -0800
Subject: [PATCH] Allow nested types inside of the <Module> type - This isn't
 disallowed by spec, although ilasm and ildasm cannot handle these cases -
 Simply skip adding the type to the available class hash.

Backport of bugfix portion of PR #111435
Fixes #111164 in .NET 9
---
 src/coreclr/vm/clsload.cpp | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/src/coreclr/vm/clsload.cpp b/src/coreclr/vm/clsload.cpp
index 0c42ca20161eee..02eecdcafd0b30 100644
--- a/src/coreclr/vm/clsload.cpp
+++ b/src/coreclr/vm/clsload.cpp
@@ -3482,6 +3482,12 @@ VOID ClassLoader::AddAvailableClassHaveLock(
     if (SUCCEEDED(pMDImport->GetNestedClassProps(classdef, &enclosing))) {
         // nested type
 
+        if (enclosing == COR_GLOBAL_PARENT_TOKEN)
+        {
+            // Types nested in the <module> class can't be found by lookup.
+            return;
+        }
+
         COUNT_T classEntryIndex = RidFromToken(enclosing) - 1;
         _ASSERTE(RidFromToken(enclosing) < RidFromToken(classdef));
         if (classEntries->GetCount() > classEntryIndex)