Cppyy doesn't recognize explicitly instantiated template when the template is a custom enum

[davidmarttila]

Platform into:

• MacOS 14.1.1 (arm64-apple-darwin23.1.0)
• clang version 18.1.8
• Python 3.11
• cppyy 3.1.2

Here's a minimal example test.cpp file for reproduction:

template<int T>
class IntTemplate {
public:
    void doSomethingInt();
};

template<> void IntTemplate<0>::doSomethingInt() {}
template class IntTemplate<0>;

enum class DemoEnum {
    A,
};

template<DemoEnum T>
class EnumTemplate {
public:
    void doSomethingEnum();
};

template<> void EnumTemplate<DemoEnum::A>::doSomethingEnum() {}
template class EnumTemplate<DemoEnum::A>;

Compile with clang++ -dynamiclib -o libtest.dylib test.cpp and run the following python code:

import cppyy
cppyy.include('test.cpp')
cppyy.load_library('test.dylib')

from cppyy.gbl import IntTemplate, EnumTemplate, DemoEnum

IntTemplate[0]() # this works

EnumTemplate[DemoEnum.A]()

Instantiating the IntTemplate works, but instantiating the EnumTemplate throws an error:

Traceback (most recent call last):
  File "/[...]/test.py", line 8, in <module>
    EnumTemplate[DemoEnum.A]()
    ~~~~~~~~~~~~^^^^^^^^^^^^
  File "[...]/python3.11/site-packages/cppyy/_cpython_cppyy.py", line 88, in __getitem__
    pyclass = _backend.MakeCppTemplateClass(*newargs)
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
TypeError: 'EnumTemplate<A>' is not a known C++ class