[PyROOT] Type `UInt64_t`/`unsigned long long` can cause problems in template resolutions

[guitargeek]

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• Checked for duplicates

Description

There was a regression in using unsigned longs in ROOT 6.32 with the cppyy upgrade.

I open the issue here because it can't be reproduced with upstream cppyy, so this is definitely a PyROOT issue.

Reproducer

import cppyy
import ROOT

cppyy.gbl.std.pair["int", "unsigned long long"]() # works!
cppyy.gbl.std.function["void(int, int)"]() # works!
cppyy.gbl.std.function["void(int, unsigned long long)"]() # doesn't work!

Gives you this output:

Traceback (most recent call last):
  File "/home/rembserj/root-support/forum/problems-with-onpartialresultslot-in-new-root-version-6-32-02/simple.py", line 6, in <module>
    cppyy.gbl.std.function["void(int, unsigned long long)"]() # doesn't work!
    ~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/rembserj/spaces/master/install/lib/root/cppyy/_cpython_cppyy.py", line 88, in __getitem__
    pyclass = _backend.MakeCppTemplateClass(*newargs)
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
TypeError: 'std::function<void(int,unsigned long long)>' is not a known C++ class

ROOT version

master

Installation method

build from source

Operating system

Arch Linux

Additional context

https://root-forum.cern.ch/t/problems-with-onpartialresultslot-in-new-root-version-6-32-02/60257

[vepadulano]

Might be related to #15872

[x0rw]

runing
cppyy.gbl.std.function["void(int, long)"]()
works fine
but cppyy.gbl.std.function["void(int, long long)"]() gives the same problem