From 291e28426c8810aa2e0b3952a4f824371099c4c4 Mon Sep 17 00:00:00 2001
From: Wei Zheng <13881045+wzchua@users.noreply.github.com>
Date: Tue, 29 Jun 2021 01:51:46 +0800
Subject: [PATCH] Fix load exception on generic covariant return type (#54790)

---
 src/coreclr/vm/class.cpp                      |  7 ++--
 .../coreclr/GitHub_54719/test54719.cs         | 32 +++++++++++++++++++
 .../coreclr/GitHub_54719/test54719.csproj     | 10 ++++++
 3 files changed, 46 insertions(+), 3 deletions(-)
 create mode 100644 src/tests/Regressions/coreclr/GitHub_54719/test54719.cs
 create mode 100644 src/tests/Regressions/coreclr/GitHub_54719/test54719.csproj

diff --git a/src/coreclr/vm/class.cpp b/src/coreclr/vm/class.cpp
index 6f2da9db3c29d..7fdf25133c12d 100644
--- a/src/coreclr/vm/class.cpp
+++ b/src/coreclr/vm/class.cpp
@@ -1170,12 +1170,13 @@ void ClassLoader::ValidateMethodsWithCovariantReturnTypes(MethodTable* pMT)
                 continue;
 
             // Locate the MethodTable defining the pParentMD.
-            while (pParentMT->GetCanonicalMethodTable() != pParentMD->GetMethodTable())
+            MethodTable* pDefinitionParentMT = pParentMT;
+            while (pDefinitionParentMT->GetCanonicalMethodTable() != pParentMD->GetMethodTable())
             {
-                pParentMT = pParentMT->GetParentMethodTable();
+                pDefinitionParentMT = pDefinitionParentMT->GetParentMethodTable();
             }
 
-            SigTypeContext context1(pParentMT->GetInstantiation(), pMD->GetMethodInstantiation());
+            SigTypeContext context1(pDefinitionParentMT->GetInstantiation(), pMD->GetMethodInstantiation());
             MetaSig methodSig1(pParentMD);
             TypeHandle hType1 = methodSig1.GetReturnProps().GetTypeHandleThrowing(pParentMD->GetModule(), &context1, ClassLoader::LoadTypesFlag::LoadTypes, CLASS_LOAD_EXACTPARENTS);
 
diff --git a/src/tests/Regressions/coreclr/GitHub_54719/test54719.cs b/src/tests/Regressions/coreclr/GitHub_54719/test54719.cs
new file mode 100644
index 0000000000000..64e60e5980085
--- /dev/null
+++ b/src/tests/Regressions/coreclr/GitHub_54719/test54719.cs
@@ -0,0 +1,32 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+
+public class IA { }
+public class IB { }
+
+public abstract class Base
+{
+    public abstract IA Key { get; }
+    public abstract IB Value { get; }
+}
+public sealed class Derived : Base<IB>
+{
+    public class A : IA { }
+    public sealed override A Key => default;
+}
+public abstract class Base<B> : Base where B : IB
+{
+    public sealed override B Value => null;
+}
+
+class Program
+{
+    static int Main()
+    {
+        new Derived();
+
+        return 100;
+    }
+}
diff --git a/src/tests/Regressions/coreclr/GitHub_54719/test54719.csproj b/src/tests/Regressions/coreclr/GitHub_54719/test54719.csproj
new file mode 100644
index 0000000000000..543d7356bbbea
--- /dev/null
+++ b/src/tests/Regressions/coreclr/GitHub_54719/test54719.csproj
@@ -0,0 +1,10 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <CLRTestKind>BuildAndRun</CLRTestKind>
+    <CLRTestPriority>1</CLRTestPriority>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="test54719.cs" />
+  </ItemGroup>
+</Project>