ClangImporter: Targeted fix for <rdar://problem/29081276>

Author: slavapestov

lib/ClangImporter/ImportDecl.cpp

@@ -3892,6 +3892,27 @@ namespace {
       }
       result->setSuperclass(superclassType);
 
+      // Mark the class as runtime-only if it is named 'OS_object', even
+      // if it doesn't have the runtime-only Clang attribute. This is a
+      // targeted fix allowing IRGen to emit convenience initializers
+      // correctly.
+      //
+      // FIXME: Remove this once SILGen gets proper support for factory
+      // initializers.
+      if (result->getName() ==
+          result->getASTContext().getIdentifier("OS_object")) {
+        result->setForeignClassKind(ClassDecl::ForeignKind::RuntimeOnly);
+      }
+
+      // If the superclass is runtime-only, our class is also. This only
+      // matters in the case above.
+      if (superclassType) {
+        auto superclassDecl = cast<ClassDecl>(superclassType->getAnyNominal());
+        auto kind = superclassDecl->getForeignClassKind();
+        if (kind != ClassDecl::ForeignKind::Normal)
+          result->setForeignClassKind(kind);
+      }
+
       // Import protocols this class conforms to.
       importObjCProtocols(result, decl->getReferencedProtocols(),
                           inheritedTypes);