[Compatibility50] Look up swift_getObjCClassMetadata at runtime.

stdlib/toolchain/Compatibility50/ProtocolConformance.cpp

@@ -20,6 +20,7 @@
 #include "Overrides.h"
 #include "../../public/runtime/Private.h"
 #include "swift/Basic/Lazy.h"
+#include <dlfcn.h>
 #include <mach-o/dyld.h>
 #include <mach-o/getsect.h>
 #include <objc/runtime.h>
@@ -89,13 +90,25 @@ static void registerAddImageCallback(void *) {
   _dyld_register_func_for_add_image(addImageCallback);
 }
 
+static const Metadata *getObjCClassMetadata(const ClassMetadata *c) {
+  // Look up swift_getObjCClassMetadata dynamically. This handles the case
+  // where the main executable can't link against libswiftCore.dylib because
+  // it will be loaded dynamically from a location that isn't known at build
+  // time.
+  using FPtr = const Metadata *(*)(const ClassMetadata *);
+  FPtr func = SWIFT_LAZY_CONSTANT(
+    reinterpret_cast<FPtr>(dlsym(RTLD_DEFAULT, "swift_getObjCClassMetadata")));
+
+  return func(c);
+}
+
 // Clone of private helper swift::_swiftoverride_class_getSuperclass
 // for use in the override implementation.
 static const Metadata *_swift50override_class_getSuperclass(
                                                     const Metadata *theClass) {
   if (const ClassMetadata *classType = theClass->getClassObject()) {
     if (classHasSuperclass(classType))
-      return getMetadataForClass(classType->Superclass);
+      return getObjCClassMetadata(classType->Superclass);
   }
 
   if (const ForeignClassMetadata *foreignClassType

test/CMakeLists.txt

@@ -205,7 +205,7 @@ foreach(SDK ${SWIFT_SDKS})
 
     # NOTE create a stub BlocksRuntime library that can be used for the
     # reflection tests
-    file(WRITE ${test_bin_dir}/BlocksRuntime.c
+    file(WRITE ${test_bin_dir}/Inputs/BlocksRuntime.c
       "void
 #if defined(_WIN32)
 __declspec(dllexport)
@@ -220,7 +220,7 @@ _Block_release(void) { }\n")
       ARCHITECTURE ${ARCH}
       SDK ${SDK}
       INSTALL_IN_COMPONENT dev
-      ${test_bin_dir}/BlocksRuntime.c)
+      ${test_bin_dir}/Inputs/BlocksRuntime.c)
     set_target_properties(BlocksRuntimeStub${VARIANT_SUFFIX} PROPERTIES
       ARCHIVE_OUTPUT_DIRECTORY ${test_bin_dir}
       LIBRARY_OUTPUT_DIRECTORY ${test_bin_dir}

test/lit.cfg

@@ -178,8 +178,8 @@ config.test_format = swift_test.SwiftTest(coverage_mode=config.coverage_mode,
                                           execute_external=not use_lit_shell)
 
 # suffixes: A list of file extensions to treat as test files.
-config.suffixes = ['.swift', '.ll', '.sil', '.gyb', '.m', '.swiftinterface',
-                   '.test-sh']
+config.suffixes = ['.swift', '.ll', '.sil', '.gyb', '.m', '.c',
+                   '.swiftinterface', '.test-sh']
 
 # excludes: A list of directories to exclude from the testsuite. The 'Inputs'
 # subdirectories contain auxiliary inputs for various tests in their parent

test/stdlib/Compatibility50Linking.c

@@ -0,0 +1,13 @@
+// RUN: %empty-directory(%t)
+// RUN: %target-clang %s -all_load %test-resource-dir/%target-sdk-name/libswiftCompatibility50.a -lobjc -o %t/main
+// RUN: %target-run %t/main
+// REQUIRES: objc_interop
+// REQUIRES: executable_test
+
+// The compatibility library needs to have no build-time dependencies on
+// libswiftCore so it can be linked into a program that doesn't link
+// libswiftCore, but will load it at runtime, such as xctest.
+//
+// Test this by linking it into a plain C program and making sure it builds.
+
+int main(void) {}