OOP: issues with parameter default values and inheritance

Summary

The code generated for the following TTCN-3 module produces several C++ compilation errors (details below).

Steps and/or TTCN-3 code to reproduce

type component CT { }

type class @trait CommonInterface {
  public function @abstract f_do_common(charstring p_test/* := "test"*/);
}

type class @abstract Base extends CommonInterface {
 public function f_do_common(charstring p_test:="test") {
    log("called from Base: "&p_test)
  } 
}

type class @final Sub extends Base {
  public function f_do_common(charstring p_test:="test") {
    log("called from Sub: "&p_test);
  } 
}

testcase tc() runs on CT {
  var Sub sub := Sub.create();
  sub.f_do_common();
  sub.f_do_common("test2");
}

control {
  execute(tc())
}

What is the current bug behavior?

There are 3 issues in the generated code:

1. The parameter default values generated for functions 'Base.f_do_common' and 'Sub.f_do_common' have the same name: 'f__do__common_p__test_defval'.
2. The type of the parameter in the 3 'f_do_common' functions are different (wrapper types are generated for parameters with default values in class methods, so they can contain references to class members). Because of this, the 3 'f_do_common' functions are interpreted as different functions by the C++ compiler, which results in 'Sub' being interpreted as an abstract class.
3. Class 'Base' inherits both 'CommonInterface' and the built-in class 'object'. Both of these inherit a separate version of 'CLASS_BASE' in C++. The compiler can't decide which of the reference counter functions ('add_ref' and 'remove_ref') inherited from 'CLASS_BASE' it should call.

What is the expected correct behavior?

The generated code should compile successfully.

Relevant logs and/or screenshots

Possible fixes

Titan version

8.2.0

Platform details (OS type and version)

Ubuntu 20.04.1

/cc @aknappqwt