'Superclass' has not been declared

[dzenanz]

It looks like #2653 introduced a regression failure in itkLabelGeometryImageFilterTest:
open.cdash.org/viewBuildError.php?onlydeltap&buildid=7354628:

In file included from /home/kitware/DashboardsITK/Modules/Nonunit/Review/test/itkLabelGeometryImageFilterTest.cxx:26:0:
/home/kitware/Dashboards/src/ITK/Modules/Nonunit/Review/test/itkLabelGeometryImageFilterTest.cxx: In function 'int LabelGeometryImageFilterTest(std::__cxx11::string, std::__cxx11::string, std::__cxx11::string, std::__cxx11::string, std::__cxx11::string)':
/home/kitware/DashboardsITK/Modules/Core/TestKernel/include/itkTestingMacros.h:69:51: error: 'Superclass' has not been declared
   std::cout << "Name of Superclass = " << object->Superclass::GetNameOfClass() << std::endl;                           \
                                                   ^
[CTest: warning matched] /home/kitware/DashboardsITK/Modules/Core/TestKernel/include/itkTestingMacros.h:69:51: note: in definition of macro 'ITK_EXERCISE_BASIC_OBJECT_METHODS'
   std::cout << "Name of Superclass = " << object->Superclass::GetNameOfClass() << std::endl;                           \
                                                   ^~~~~~~~~~
/home/kitware/DashboardsITK/Modules/Core/TestKernel/include/itkTestingMacros.h:79:28: error: 'Superclass' has not been declared
   if (!std::strcmp(object->Superclass::GetNameOfClass(), #SuperclassName))                                             \
                            ^
[CTest: warning matched] /home/kitware/DashboardsITK/Modules/Core/TestKernel/include/itkTestingMacros.h:79:28: note: in definition of macro 'ITK_EXERCISE_BASIC_OBJECT_METHODS'
   if (!std::strcmp(object->Superclass::GetNameOfClass(), #SuperclassName))                                             \
                            ^~~~~~~~~~

This was also encountered earlier, #2319 attempted to clarify the error message.

[dzenanz]

From Lee

Because Superclass is an alias rather than the actual name of the base class, that could be causing trouble for some compilers. For example, often we have to use the typename keyword to refer to an alias defined with using within a class so that the compiler knows that the alias is a type rather than a data member or member function. So, instead of

object->Superclass::GetNameOfClass()

I might have written

static_cast<const typename decltype(*object)::Superclass *>(object)->GetNameOfClass()

with the explicit typename (and perhaps without the const if we are guaranteed that object won't be const).

[dzenanz]

From Lee

I've tried my own suggestion static_cast<const typename decltype(*object)::Superclass *>(object)->GetNameOfClass() on my Ubuntu 20.04 machine with gcc-10.3.0 and it does not work. The issue appears to be that decltype(*object) is not well defined during the declaration of object; for example when an (inline) method is defined within a class declaration rather than as a separate definition, which is quite common for ITK's templated classes.

[Leengit]

Not understanding a using statement defined within a class declaration to refer to the superclass is also a piece of the problem with #2759 / #2780. There the solution to make VS2017 happy is to replace the definition of a member function (outside the class declaration; that is, in a *.hxx file) so that the type is trailing (->) rather than before the function name. Here the solution to make GCC happy (#2653) is to strip out the offending code for the offending compiler. I don't see how the solution for #2759 / #2780 would apply here, but am raising the possibility that there is something to be gleaned, in the hopes that it triggers an aha moment for any of you smart folks out there.

[dzenanz]

Workaround applied by #2720.