Add an executable test for objc_runtime_visible classes + dynamic casting.

Author: DougGregor

test/Interpreter/SDK/Inputs/custom-modules/DispatchObjects.h

@@ -0,0 +1,13 @@
+__attribute__((objc_runtime_visible))
+@interface OS_dispatch_queue
+@end
+
+__attribute__((objc_runtime_visible))
+@interface OS_object
+@end
+
+__attribute__((objc_runtime_visible))
+@interface OS_dispatch_source
+@end
+
+id dispatch_get_current_queue(void);

test/Interpreter/SDK/Inputs/custom-modules/module.map

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+module DispatchObjects {
+  header "DispatchObjects.h"
+}

test/Interpreter/SDK/OS_objects.swift

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+// RUN: rm -rf %t
+// RUN: mkdir -p %t
+//
+// RUN: cp %s %t/main.swift
+// RUN: %target-build-swift %t/main.swift -I %S/Inputs/custom-modules/ -o %t/OS_objects -Xfrontend -disable-access-control
+// RUN: %target-run %t/OS_objects 2>&1 | FileCheck %s
+
+// REQUIRES: objc_interop
+
+// Note: Test the use of the Clang objc_runtime_visible attribute via
+// known OS objects on Darwin.
+
+import ObjectiveC
+import DispatchObjects
+
+// CHECK: Get current queue
+print("Get current queue")
+let obj = dispatch_get_current_queue();
+
+// CHECK-NEXT: Object is a dispatch queue
+if let q = obj as? OS_dispatch_queue {
+  print("Object is a dispatch queue")
+}
+
+// CHECK-NEXT: Object is an OS object
+if let q = obj as? OS_object {
+  print("Object is an OS object")
+}
+
+// CHECK-NEXT: Object is an NSObject
+if let q = obj as? NSObject {
+  print("Object is an NSObject")
+}
+
+// CHECK-NEXT: Object is not a dispatch source
+if let q = obj as? OS_dispatch_source {
+  print("Object is a dispatch source!?!?")
+} else {
+  print("Object is not a dispatch source")
+}
+
+// CHECK-NEXT: DONE
+print("DONE");