Fix for issue 23908 - error message reports the exact error when a native extension fails to load.

runtime/bin/extensions_macos.cc

Index: runtime/bin/extensions_macos.cc
diff --git a/runtime/bin/extensions_macos.cc b/runtime/bin/extensions_macos.cc
index 92a5e98cc216ec13291a73bc59a46c1920e26dad..7db0b9a2168573f27e9e3783af91dbae9faf5147 100644
--- a/runtime/bin/extensions_macos.cc
+++ b/runtime/bin/extensions_macos.cc
@@ -15,15 +15,27 @@ namespace bin {
 const char* kPrecompiledLibraryName = "libprecompiled.dylib";
 const char* kPrecompiledSymbolName = "kInstructionsSnapshot";
 
-void* Extensions::LoadExtensionLibrary(const char* library_file) {
-  return dlopen(library_file, RTLD_LAZY);
+Dart_Handle Extensions::LoadExtensionLibrary(const char* library_file,
+                                             void** library_handle) {
+  ASSERT(library_handle != NULL);
+  *library_handle = dlopen(library_file, RTLD_LAZY);
+  if (*library_handle == NULL) {
+    return Dart_NewApiError(dlerror());
+  }
+  return Dart_Null();
 }
 
-void* Extensions::ResolveSymbol(void* lib_handle, const char* symbol) {
+Dart_Handle Extensions::ResolveSymbol(void* lib_handle,
+                                      const char* symbol,
+                                      void** init_function) {
+  ASSERT(init_function != NULL);
   dlerror();
-  void* result = dlsym(lib_handle, symbol);
-  if (dlerror() != NULL) return NULL;
-  return result;
+  *init_function = dlsym(lib_handle, symbol);
+  char* err_str = dlerror();
+  if (err_str != NULL) {
+    return Dart_NewApiError(err_str);
+  }
+  return Dart_Null();
 }
 
 }  // namespace bin