[move-only] Conditionalize TBDGen's special handling of class destructors just for classes.

Otherwise it triggers for non-class nominal move only types as well, which we do
not want.

Author: gottesmm

lib/TBDGen/TBDGen.cpp

@@ -999,15 +999,16 @@ void TBDGenVisitor::visitConstructorDecl(ConstructorDecl *CD) {
 }
 
 void TBDGenVisitor::visitDestructorDecl(DestructorDecl *DD) {
-  // Class destructors come in two forms (deallocating and non-deallocating),
-  // like constructors above. This is the deallocating one:
+  // Destructors come in two forms (deallocating and non-deallocating), like
+  // constructors above. Classes use both but move only non-class nominal types
+  // only use the deallocating one. This is the deallocating one:
   visitAbstractFunctionDecl(DD);
 
-  auto parentClass = DD->getParent()->getSelfClassDecl();
-
-  // But the non-deallocating one doesn't apply to some @objc classes.
-  if (!Lowering::usesObjCAllocator(parentClass)) {
-    addSymbol(SILDeclRef(DD, SILDeclRef::Kind::Destroyer));
+  if (auto parentClass = DD->getParent()->getSelfClassDecl()) {
+    // But the non-deallocating one doesn't apply to some @objc classes.
+    if (!Lowering::usesObjCAllocator(parentClass)) {
+      addSymbol(SILDeclRef(DD, SILDeclRef::Kind::Destroyer));
+    }
   }
 }