check if file opening failed

Phys/FunctorCore/src/Components/Factory.cpp

@@ -165,10 +165,14 @@ struct FunctorFactory : public extends<Service, Functors::IFactory> {
     } else {
       auto const cpp_filename = m_jit_lib_dir + file_prefix + ".cpp";
       info() << "New functor library will be created." << endmsg;
-      if ( msgLevel( MSG::DEBUG ) ) { debug() << "Generated C++ filename: " << cpp_filename << endmsg; }
+      if ( msgLevel( MSG::DEBUG ) ) { debug() << "Generating C++ file: " << cpp_filename << endmsg; }
 
       {
-        std::ofstream out( cpp_filename );
+        std::ofstream out{cpp_filename};
+        if ( !out.is_open() ) {
+          throw GaudiException{ "Failed to open file " + cpp_filename, "FunctorFactory",
+                                StatusCode::FAILURE };
+        }
         out << full_lib_code;
         out.close();
       }