IRGen: Take enable-testing into account when computing whether a class has resilient metadata

lib/IRGen/ClassMetadataVisitor.h

@@ -116,7 +116,17 @@ template <class Impl> class ClassMetadataVisitor
       if (superclassDecl->hasClangNode()) {
         // Nothing to do; Objective-C classes do not add new members to
         // Swift class metadata.
-      } else if (IGM.hasResilientMetadata(superclassDecl, ResilienceExpansion::Maximal)) {
+
+      // Super class metadata is resilient if
+      // the superclass is resilient when viewed from the currrent module.
+      // But not if the current class is defined in an external module and
+      //    not publically accessible (e.g private or internal). This would
+      //    normally not happen except if we compile theClass's module with
+      //    enable-testing.
+      } else if (IGM.hasResilientMetadata(superclassDecl, ResilienceExpansion::Maximal) &&
+                 (theClass->getModuleContext() == IGM.getSwiftModule() ||
+                 theClass->getFormalAccessScope(/*useDC=*/nullptr,
+                            /*treatUsableFromInlineAsPublic=*/true).isPublic())) {
         // Runtime metadata instantiation will initialize our field offset
         // vector and vtable entries.
         //

test/IRGen/Inputs/resilient-class.swift

@@ -0,0 +1,7 @@
+open class Base {
+    var x = 1
+}
+
+internal class SubClass : Base {
+    var y = 2
+}

test/IRGen/testing-enabled-resilient-super-class.swift

@@ -0,0 +1,20 @@
+// RUN: %empty-directory(%t)
+// RUN: %target-swift-frontend -enable-testing -enable-library-evolution -module-name=resilient %S/Inputs/resilient-class.swift -emit-module -emit-module-path %t/resilient.swiftmodule
+// RUN: %target-swift-frontend -I %t -emit-ir %s | %FileCheck %s
+
+// Check that linking succeeds.
+// RUN: %empty-directory(%t)
+// RUN: %target-build-swift-dylib(%t/%target-library-name(resilient)) %S/Inputs/resilient-class.swift -module-name resilient -emit-module -emit-module-path %t/resilient.swiftmodule -enable-library-evolution -enable-testing
+// RUN: %target-build-swift -I %t -L %t -lresilient %s -o %t/main %target-rpath(%t)
+// RUN: %target-build-swift -O -I %t -L %t -lresilient %s -o %t/main %target-rpath(%t)
+
+@testable import resilient
+
+// Don't access via the class offset global. Use a fragile access pattern instead.
+
+// CHECK-NOT: s9resilient8SubClassCMo
+
+public func testCase() {
+  let t = SubClass()
+  print(t.y)
+}