Add test for weak-linked Objective-C resilient class stubs

Author: slavapestov

validation-test/Runtime/Inputs/class-stubs-weak/first.swift

@@ -0,0 +1,11 @@
+import Foundation
+
+open class BaseClass : NSObject {
+  @objc dynamic open func instanceMethod() -> Int {
+    return 42
+  }
+
+  @objc dynamic open class func classMethod() -> Int {
+    return 31337
+  }
+}

validation-test/Runtime/Inputs/class-stubs-weak/module.map

@@ -0,0 +1,3 @@
+module first {
+  header "first.h"
+}

validation-test/Runtime/Inputs/class-stubs-weak/second.swift

@@ -0,0 +1,5 @@
+import first
+
+#if BEFORE
+@_weakLinked public class DerivedClass : BaseClass {}
+#endif

validation-test/Runtime/class_stubs_weak.m

@@ -0,0 +1,50 @@
+// Check that Objective-C is able to use a resilient class stub emitted
+// by the Swift compiler.
+
+// RUN: %empty-directory(%t)
+// RUN: %target-build-swift -emit-library -emit-module -o %t/libfirst.dylib -emit-objc-header-path %t/first.h %S/Inputs/class-stubs-weak/first.swift -Xlinker -install_name -Xlinker @executable_path/libfirst.dylib -enable-library-evolution
+// RUN: %target-build-swift -emit-library -o %t/libsecond.dylib -emit-objc-header-path %t/second.h -I %t %S/Inputs/class-stubs-weak/second.swift -Xlinker -install_name -Xlinker @executable_path/libsecond.dylib -lfirst -L %t -Xfrontend -enable-resilient-objc-class-stubs -DBEFORE
+// RUN: cp %S/Inputs/class-stubs-weak/module.map %t/
+// RUN: xcrun %clang %s -I %t -L %t -fmodules -fobjc-arc -o %t/main -lfirst -lsecond -Wl,-U,_objc_loadClassref
+
+// Now rebuild the library, omitting the weak-exported class
+// RUN: %target-build-swift -emit-library -o %t/libsecond.dylib -I %t %S/Inputs/class-stubs-weak/second.swift -Xlinker -install_name -Xlinker @executable_path/libsecond.dylib -lfirst -L %t -Xfrontend -enable-resilient-objc-class-stubs
+
+// RUN: %target-codesign %t/main %t/libfirst.dylib %t/libsecond.dylib
+// RUN: %target-run %t/main %t/libfirst.dylib %t/libsecond.dylib
+
+// REQUIRES: executable_test
+// REQUIRES: objc_interop
+
+#import <dlfcn.h>
+#import <stdio.h>
+#import "second.h"
+
+@implementation DerivedClass (MyCategory)
+
+- (int)instanceMethod {
+  return [super instanceMethod] + 1;
+}
+
++ (int)classMethod {
+  return [super classMethod] + 1;
+}
+
+@end
+
+int main(int argc, const char * const argv[]) {
+  // Only test the new behavior on a new enough libobjc.
+  if (!dlsym(RTLD_NEXT, "_objc_loadClassref")) {
+    fprintf(stderr, "skipping evolution tests; OS too old\n");
+    return EXIT_SUCCESS;
+  }
+
+  Class cls = [DerivedClass class];
+  if (cls) {
+    printf("Class is not null");
+    return EXIT_FAILURE;
+  }
+
+  printf("Class is null");
+  return EXIT_SUCCESS;
+}