[mono][metadata] Fixes for static virtual methods with interface variance

src/mono/mono/metadata/class-setup-vtable.c

@@ -1035,6 +1035,37 @@ apply_override (MonoClass *klass, MonoClass *override_class, MonoMethod **vtable
 	return TRUE;
 }
 
+/*
+ * Interface method `decl` is overridden in `klass` with `override`. In addition to overriding the method slot
+ * for this interface method, if parent klass implements a different variant compatible interface, then we also
+ * need to override the correpsonding method slot in this other interface.
+ */
+static void
+apply_override_variant_interface (MonoClass *klass, MonoMethod *decl, MonoMethod *override, MonoMethod **vtable)
+{
+	MonoClass *parent = klass->parent;
+
+	// This handles variant overrides for static virtual methods only
+	if (!m_method_is_static (decl))
+		return;
+
+	if (mono_class_has_variant_generic_params (decl->klass) && parent) {
+		for (int k = 0; k < klass->parent->interface_offsets_count; k++) {
+			MonoClass *impl_itf = parent->interfaces_packed [k];
+			if (decl->klass != impl_itf &&
+					mono_class_has_variant_generic_params (impl_itf) &&
+					mono_class_get_generic_type_definition (impl_itf) == mono_class_get_generic_type_definition (decl->klass)) {
+				if (mono_class_is_variant_compatible (impl_itf, decl->klass, FALSE)) {
+					int vt_slot = parent->interface_offsets_packed [k] + decl->slot;
+					vtable [vt_slot] = override;
+					TRACE_INTERFACE_VTABLE (printf ("\tvariance override slot %d with method %s\n", vt_slot, mono_method_full_name (override, TRUE)));
+					break;
+				}
+			}
+		}
+	}
+}
+
 static void
 handle_dim_conflicts (MonoMethod **vtable, MonoClass *klass, GHashTable *conflict_map)
 {
@@ -1788,6 +1819,7 @@ mono_class_setup_vtable_general (MonoClass *klass, MonoMethod **overrides, int o
 			g_assert (override->klass == klass);
 			if (!apply_override (klass, klass, vtable, decl, override, &override_map, &override_class_map, &conflict_map))
 				goto fail;
+			apply_override_variant_interface (klass, decl, override, vtable);
 		}
 	}
 

src/mono/mono/metadata/class.c

@@ -1921,6 +1921,31 @@ mono_class_interface_offset (MonoClass *klass, MonoClass *itf)
 	return -1;
 }
 
+static MonoClass*
+lookup_variant_compatible_interface (MonoClass *klass, MonoClass *itf)
+{
+	if (!m_class_is_interfaces_inited (klass)) {
+		ERROR_DECL(error);
+		mono_class_setup_interfaces (klass, error);
+		if (!is_ok (error)) {
+			mono_error_cleanup (error);
+			return NULL;
+		}
+	}
+	for (int i = 0; i < m_class_get_interface_count (klass); i++) {
+		MonoClass *impl_itf = m_class_get_interfaces (klass) [i];
+		if (mono_class_is_variant_compatible (itf, impl_itf, FALSE))
+			return impl_itf;
+
+		// Look up also in all the interfaces it implements
+		impl_itf = lookup_variant_compatible_interface (impl_itf, itf);
+		if (impl_itf)
+			return impl_itf;
+	}
+
+	return NULL;
+}
+
 /**
  * mono_class_interface_offset_with_variance:
  *
@@ -1973,11 +1998,19 @@ mono_class_interface_offset_with_variance (MonoClass *klass, MonoClass *itf, gbo
 	if (!mono_class_has_variant_generic_params (itf))
 		return -1;
 
-	for (i = 0; i < klass_interface_offsets_count; i++) {
-		if (mono_class_is_variant_compatible (itf, m_class_get_interfaces_packed (klass) [i], FALSE)) {
+	// Look up first variant interface in the current class, and then in parent slots.
+	while (klass) {
+		MonoClass *impl_itf = lookup_variant_compatible_interface (klass, itf);
+		if (impl_itf) {
+			// Found compatible implemented interface. Look up its slot in the vtable
 			*non_exact_match = TRUE;
-			return m_class_get_interface_offsets_packed (klass) [i];
+			for (i = 0; i < klass_interface_offsets_count; i++) {
+				if (m_class_get_interfaces_packed (klass) [i] == impl_itf)
+					return m_class_get_interface_offsets_packed (klass) [i];
+			}
 		}
+
+		klass = m_class_get_parent (klass);
 	}
 
 	return -1;

src/tests/issues.targets

@@ -1192,9 +1192,6 @@
         <ExcludeList Include="$(XunitTestBinBase)/Loader/classloader/StaticVirtualMethods/Reabstraction/**">
             <Issue>https://github.com/dotnet/runtime/issues/88775</Issue>
         </ExcludeList>
-        <ExcludeList Include="$(XunitTestBinBase)/Loader/classloader/StaticVirtualMethods/InterfaceVariance/**">
-            <Issue>https://github.com/dotnet/runtime/issues/88689</Issue>
-        </ExcludeList>
         <ExcludeList Include="$(XunitTestBinBase)/Regressions/coreclr/GitHub_85240/test85240/**">
             <Issue>https://github.com/dotnet/runtime/issues/71095</Issue>
         </ExcludeList>
@@ -1297,9 +1294,6 @@
         <ExcludeList Include="$(XunitTestBinBase)/Loader/classloader/StaticVirtualMethods/DiamondShape/**">
             <Issue>https://github.com/dotnet/runtime/issues/80350</Issue>
         </ExcludeList>
-        <ExcludeList Include="$(XunitTestBinBase)/Loader/classloader/StaticVirtualMethods/InterfaceVariance/**">
-            <Issue>Static virtual methods are not yet implemented in the Mono runtime.</Issue>
-        </ExcludeList>
         <ExcludeList Include="$(XunitTestBinBase)/Loader/classloader/StaticVirtualMethods/NegativeTestCases/**">
             <Issue>Static virtual methods are not yet implemented in the Mono runtime.</Issue>
         </ExcludeList>