itkMacros less robust / break external code that also has an itk namespace

[kislinsk]

Description

In 24e7b45, leading colons for namespaces have been removed with an automated search and replace. Unfortunately this also affected some macros and made them less robust resp. introduced a regression. We have a few projects that also have itk (sub-)namespaces and the lookup for classes like LightObject and ObjectFactory used in macros like itkNewMacro() is now broken in these cases. It is not a compiler-specific issue as it happens on MSVC, gcc, and clang.

Expected behavior

Macros always should be as robust as possible in particular regarding parenthesis or namespaces.

Versions

Worked in ITK v5.2.1, broken in ITK v5.3.0.

Environment

Windows, Ubuntu, macOS, MSVC, GCC, clang.

Additional Information

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[dzenanz]

Having a minimal example demonstrating the problem would probably be helpful. @Leengit could you tackle this without a demonstrative example?

[kislinsk]

Here's a minimal example:

example.cpp:

#include <itkLightObject.h>
#include <itkObjectFactory.h>

namespace example
{
  namespace itk
  {
    // These two lines shouldn't be necessary and weren't until ITK v5.3.0.
    // Please keep the absolute ::itk namespaces in macros like itkNewMacro().
    using LightObject = ::itk::LightObject;
    template<typename T> using ObjectFactory = ::itk::ObjectFactory<T>;

    class Example : public ::itk::LightObject
    {
    public:
      using Self = Example;

      itkTypeMacro(Example, ::itk::LightObject)
      itkNewMacro(Self)

    protected:
      Example() = default;
      ~Example() override = default;
    };
  }
}

CMakeLists.txt:

cmake_minimum_required(VERSION 3.16.3...3.19.7 FATAL_ERROR)
project(Example)
find_package(ITK 5.3 REQUIRED COMPONENTS ITKCommon)
add_library(example example.cpp)
target_link_libraries(example PRIVATE ITKCommon)

[thewtex]

@kislinsk thanks for the report. Can you please verify that #4087 addresses your use case?

[kislinsk]

@thewtex Thanks, it works!

Not an issue for us but you may want to consider to do the same for the std namespace in macros.

[thewtex]

@kislinsk thanks for the verification!

Good idea regarding std -- let's add that if it is found that it is needed.