Add default method support to virtual statics (#64717)

- The preview feature version of virtual statics implemented for .NET 6 does not allow for the interface methods to have a default implementation.
- With this change, we add support for the interface method having an actual implementation to CoreCLR. From what I can tell the Mono runtime already had such support
- There are some small ECMA spec updates to allow this change that are also included

In addition, I've taken the liberty to enable running the coreclr test suite on Mono on Windows. It needed a small amount of fixup.

docs/design/specs/Ecma-335-Augments.md

@@ -453,7 +453,7 @@ https://www.ecma-international.org/publications-and-standards/standards/ecma-335
 
 (Add second paragraph)
 
-Static interface methods may be marked as virtual. Valid object types implementing such interfaces shall provide implementations
+Static interface methods may be marked as virtual. Valid object types implementing such interfaces may provide implementations
 for these methods by means of Method Implementations (II.15.1.4). Polymorphic behavior of calls to these methods is facilitated
 by the constrained. call IL instruction where the constrained. prefix specifies the type to use for lookup of the static interface
 method.
@@ -531,7 +531,6 @@ or static method actually implemented directly on the type.
 (Add to the end of the 1st paragraph)
 
 Interfaces may define static virtual methods that get resolved at runtime based on actual types involved.
-These static virtual methods must be marked as abstract in the defining interfaces.
 
 ### II.12.2 Implementing virtual methods on interfaces
 
@@ -754,7 +753,7 @@ the call itself doesn't involve any instance or `this` pointer.
 (Edit bulleted section "This contains informative text only" starting at the bottom of page
 233):
 
-Edit section *7.b*: Static | Virtual | !Abstract
+Remove section *7.b*: ~~Static | Virtual~~
 
 (Add new section 41 after the last section 40:)
 

src/coreclr/vm/genericdict.cpp

@@ -1081,10 +1081,11 @@ Dictionary::PopulateEntry(
 #if FEATURE_DEFAULT_INTERFACES
                 // If we resolved the constrained call on a value type into a method on a reference type, this is a
                 // default interface method implementation.
+                // If the method is a static method, this is ok, but for instance methods there are boxing issues.
                 // In such case we would need to box the value type before we can dispatch to the implementation.
                 // This would require us to make a "boxing stub". For now we leave the boxing stubs unimplemented.
                 // It's not clear if anyone would need them and the implementation complexity is not worth it at this time.
-                if (!pResolvedMD->GetMethodTable()->IsValueType() && constraintType.GetMethodTable()->IsValueType())
+                if (!pResolvedMD->IsStatic() && !pResolvedMD->GetMethodTable()->IsValueType() && constraintType.GetMethodTable()->IsValueType())
                 {
                     SString assemblyName;
 

src/coreclr/vm/methodtable.cpp

@@ -7580,7 +7580,6 @@ MethodTable::ResolveVirtualStaticMethod(MethodTable* pInterfaceType, MethodDesc*
                 {
                     canonicalEquivalentFound = true;
                     break;
-                    return NULL;
                 }
             }
         }
@@ -7644,6 +7643,12 @@ MethodTable::ResolveVirtualStaticMethod(MethodTable* pInterfaceType, MethodDesc*
                 }
             }
         }
+
+        // Default implementation logic, which only kicks in for default implementations when lookin up on an exact interface target
+        if (!pInterfaceMD->IsAbstract() && !(this == g_pCanonMethodTableClass) && !IsSharedByGenericInstantiations())
+        {
+            return pInterfaceMD->FindOrCreateAssociatedMethodDesc(pInterfaceMD, pInterfaceType, FALSE, pInterfaceMD->GetMethodInstantiation(), FALSE);
+        }
     }
 
     if (allowNullResult)
@@ -7818,7 +7823,7 @@ MethodTable::VerifyThatAllVirtualStaticMethodsAreImplemented()
                 MethodDesc *pMD = it.GetMethodDesc();
                 if (pMD->IsVirtual() &&
                     pMD->IsStatic() &&
-                    !ResolveVirtualStaticMethod(pInterfaceMT, pMD, /* allowNullResult */ TRUE, /* verifyImplemented */ TRUE, /* allowVariantMatches */ FALSE))
+                    (pMD->IsAbstract() && !ResolveVirtualStaticMethod(pInterfaceMT, pMD, /* allowNullResult */ TRUE, /* verifyImplemented */ TRUE, /* allowVariantMatches */ FALSE)))
                 {
                     IMDInternalImport* pInternalImport = GetModule()->GetMDImport();
                     GetModule()->GetAssembly()->ThrowTypeLoadException(pInternalImport, GetCl(), pMD->GetName(), IDS_CLASSLOAD_STATICVIRTUAL_NOTIMPL);

src/coreclr/vm/methodtablebuilder.cpp

@@ -5076,7 +5076,7 @@ MethodTableBuilder::ValidateMethods()
         // Virtual static methods are only allowed on interfaces and they must be abstract.
         if (IsMdStatic(it.Attrs()) && IsMdVirtual(it.Attrs()))
         {
-            if (!IsInterface() || !IsMdAbstract(it.Attrs()))
+            if (!IsInterface())
             {
                 BuildMethodTableThrowException(IDS_CLASSLOAD_STATICVIRTUAL, it.Token());
             }

src/coreclr/vm/typedesc.cpp

@@ -1613,7 +1613,7 @@ BOOL TypeVarTypeDesc::SatisfiesConstraints(SigTypeContext *pTypeContextOfConstra
                                 MethodDesc *pMD = it.GetMethodDesc();
                                 if (pMD->IsVirtual() &&
                                     pMD->IsStatic() &&
-                                    !thElem.AsMethodTable()->ResolveVirtualStaticMethod(pInterfaceMT, pMD, /* allowNullResult */ TRUE, /* verifyImplemented */ TRUE))
+                                    (pMD->IsAbstract() && !thElem.AsMethodTable()->ResolveVirtualStaticMethod(pInterfaceMT, pMD, /* allowNullResult */ TRUE, /* verifyImplemented */ TRUE)))
                                 {
                                     virtualStaticResolutionCheckFailed = true;
                                     break;

src/tests/Common/Directory.Build.targets

@@ -172,7 +172,8 @@
     </ItemGroup>
 
     <ItemGroup Condition="'$(RuntimeFlavor)' == 'mono' and '$(IsDesktopOS)' == 'true' " >
-      <RuntimeDependencyCopyLocal Include="$(MonoArtifactsPath)/libcoreclr$(LibSuffix)" TargetDir=""  />
+      <RuntimeDependencyCopyLocal Condition="'$(TargetOS)' != 'windows'" Include="$(MonoArtifactsPath)/libcoreclr$(LibSuffix)" TargetDir=""  />
+      <RuntimeDependencyCopyLocal Condition="'$(TargetOS)' == 'windows'" Include="$(MonoArtifactsPath)coreclr$(LibSuffix)" TargetDir=""  />
       <RuntimeDependencyCopyLocal Include="$(MonoArtifactsPath)/libmono-component-*" TargetDir=""  />
        <RuntimeDependencyCopyLocal Include="$(MonoArtifactsPath)/*.dll" TargetDir="/"  />
     </ItemGroup>