Fix a case in MethodImpl overriding which wasn't handled as expected in ilc.exe for native aot (#106716)

* Fix a case in MethodImpl overriding which wasn't handled as expected in ilc.exe for native aot
- This was causing real C# applications to fail to behave correctly on NativeAOT builds
- Enable testing for covariant byref returns on nativeaot (split testing up so that the tests do not expect TypeLoadException, which NativeAOT doesn't reliably generate)
- Put copy of attributetesting.il test into the managed type system unit test suite
- Add regression test of issue noted in #96175 into managed type system unit test suite
- Update workflow documentation to include a better path to finding details on how to run CoreCLR and Libraries tests for Native AOT

Fixes #96175

Author: davidwrighton

docs/workflow/README.md

@@ -78,12 +78,14 @@ Now you know about configurations and how we use them, so now you will want to r
 
 * [Building CoreCLR runtime](/docs/workflow/building/coreclr/README.md)
 * [Building Mono runtime](/docs/workflow/building/mono/README.md)
+* [Building NativeAOT runtime](/docs/workflow/building/coreclr/nativeaot.md)
 * [Building Libraries](/docs/workflow/building/libraries/README.md)
 
 After that, here's information about how to run tests:
 
 * [Testing CoreCLR runtime](/docs/workflow/testing/coreclr/testing.md)
 * [Testing Mono runtime](/docs/workflow/testing/mono/testing.md)
+* [Testing NativeAOT runtime](/docs/workflow/building/coreclr/nativeaot.md#running-tests)
 * [Testing Libraries](/docs/workflow/testing/libraries/testing.md)
 
 And how to measure performance:

docs/workflow/building/coreclr/nativeaot.md

@@ -87,6 +87,8 @@ If you haven't built the tests yet, run `src\tests\build.cmd nativeaot [Debug|Re
 
 To run all the tests that got built, run `src\tests\run.cmd runnativeaottests [Debug|Release]` on Windows, or `src/tests/run.sh --runnativeaottests [Debug|Release]` on Linux. The `Debug`/`Release` flag should match the flag that was passed to `build.cmd` in the previous step.
 
+To build an individual test, follow the instructions for compiling a individual test project located in [Building an Individual Test](/docs/workflow/testing/coreclr/testing.md#building-an-individual-test), but add `/t:BuildNativeAot /p:TestBuildMode=nativeaot` to the build command.
+
 To run an individual test (after it was built), navigate to the `artifacts\tests\coreclr\[windows|linux|osx[.x64.[Debug|Release]\$path_to_test` directory. `$path_to_test` matches the subtree of `src\tests`. You should see a `[.cmd|.sh]` file there. This file is a script that will compile and launch the individual test for you. Before invoking the script, set the following environment variables:
 
 * CORE_ROOT=$repo_root\artifacts\tests\coreclr\[windows|linux|osx].x64.[Debug|Release]\Tests\Core_Root

src/coreclr/tools/Common/TypeSystem/Common/MetadataVirtualMethodAlgorithm.cs

@@ -461,7 +461,26 @@ private static void FindBaseUnificationGroup(MetadataType currentType, Unificati
             // Unless the current type has a name/sig match for the group, look to the base type to define the unification group further
             if ((nameSigMatchMethod == null) && (baseType != null))
             {
+                // TODO! Consider if we should do this check even if the virtual name/sig match finds something.
+                // We may want to build up a unification group for the base just to check the further MethodImpl case here.
                 FindBaseUnificationGroup(baseType, unificationGroup);
+
+                // We should check to see if a the DefiningMethod on the base unification group is overriden via MethodImpl
+                // TODO! check to see if we need to check for MethodImpls affecting other members of the unification group
+                // other than the defining method
+                if (unificationGroup.DefiningMethod != null)
+                {
+                    methodImpl = FindImplFromDeclFromMethodImpls(currentType, unificationGroup.DefiningMethod);
+                    if (methodImpl != null)
+                    {
+                        if (methodImpl.RequiresSlotUnification())
+                        {
+                            unificationGroup.AddMethodRequiringSlotUnification(unificationGroup.DefiningMethod);
+                            unificationGroup.AddMethodRequiringSlotUnification(methodImpl);
+                        }
+                        unificationGroup.SetDefiningMethod(methodImpl);
+                    }
+                }
             }
 
             Debug.Assert(unificationGroup.IsInGroupOrIsDefiningSlot(originalDefiningMethod));

src/coreclr/tools/aot/ILCompiler.TypeSystem.Tests/CoreTestAssembly/Platform.cs

@@ -247,11 +247,17 @@ public static class RuntimeFeature
         public const string ByRefLikeGenerics = nameof(ByRefLikeGenerics);
         public const string UnmanagedSignatureCallingConvention = nameof(UnmanagedSignatureCallingConvention);
         public const string VirtualStaticsInInterfaces = nameof(VirtualStaticsInInterfaces);
+        public const string CovariantReturnsOfClasses = "CovariantReturnsOfClasses";
     }
 
     internal sealed class IntrinsicAttribute : Attribute
     {
     }
+
+    public sealed partial class PreserveBaseOverridesAttribute : System.Attribute
+    {
+        public PreserveBaseOverridesAttribute() { }
+    }
 }
 
 namespace System.Runtime.Intrinsics

src/coreclr/tools/aot/ILCompiler.TypeSystem.Tests/CoreTestAssembly/VirtualFunctionOverride.cs

@@ -60,4 +60,44 @@ unsafe class FunctionPointerOverloadDerived : FunctionPointerOverloadBase
         public override Type Method(delegate* unmanaged[Stdcall, SuppressGCTransition]<void> p) => null;
         public override Type Method(delegate*<void> p) => null;
     }
+
+    class BaseCovariant
+    {
+        public virtual BaseCovariant FromType()
+        {
+            return new BaseCovariant();
+        }
+    }
+
+    class ImplCovariant : BaseCovariant
+    {
+        public override ImplCovariant FromType()
+        {
+            return new ImplCovariant();
+        }
+    }
+
+    class SubImplCovariant : ImplCovariant
+    {
+        public override SubImplCovariant FromType()
+        {
+            return new SubImplCovariant();
+        }
+    }
+
+    class SubImplCovariant2 : ImplCovariant
+    {
+        public override ImplCovariant FromType()
+        {
+            return new ImplCovariant();
+        }
+    }
+
+    class SubSubImplCovariant : SubImplCovariant2
+    {
+        public override SubSubImplCovariant FromType()
+        {
+            return new SubSubImplCovariant();
+        }
+    }
 }

src/coreclr/tools/aot/ILCompiler.TypeSystem.Tests/ILTestAssembly/ILTestAssembly.ilproj

@@ -19,6 +19,7 @@
     <Compile Include="Signature.il" />
     <Compile Include="MethodImplOverride1.il" />
     <Compile Include="MDArrayFunctionResolution.il" />
+    <Compile Include="PreserveBaseOverridesAttibuteTesting.il" />
   </ItemGroup>
 
 </Project>