When running bdist_wheel on Windows, warning appears: "Config variable 'Py_DEBUG' is unset, Python ABI tag may be incorrect"

Note that this issue is related to https://github.com/pypa/wheel/issues/171 .

When building a wheel with "python -m build --wheel" on Windows, it ends up executing wheel/bdist_wheel.py, and outputs this warning to screen:

C:\temp\build-env-wi_m8kpm\lib\site-packages\wheel\bdist_wheel.py:80: RuntimeWarning: Config variable 'Py_DEBUG' is unset, Python ABI tag may be incorrect
  if get_flag('Py_DEBUG',

This is because wheel/src/wheel/bdist_wheel.py has a local implementation of get_abi_tag() that's called by bdist_wheel.get_tag(), which is called by bdist_wheel.run(). This local implementation isn't able to detect the debug attribute properly on Windows, so it issues a warning.

But wheel/src/wheel/vendored/packaging/tags.py has another implementation of this functionality in _cpython_abis() that detects the debug attribute more correctly:

    debug = pymalloc = ucs4 = ""
    with_debug = _get_config_var("Py_DEBUG", warn)
    has_refcount = hasattr(sys, "gettotalrefcount")
    # Windows doesn't set Py_DEBUG, so checking for support of debug-compiled
    # extension modules is the best option.
    # https://github.com/pypa/pip/issues/3383#issuecomment-173267692
    has_ext = "_d.pyd" in EXTENSION_SUFFIXES
    if with_debug or (with_debug is None and (has_refcount or has_ext)):
        debug = "d"

tags._cpython_abis() is called by tags.cpython_tags(), which is called by tags.sys_tags(). See https://github.com/pypa/packaging/issues/194 and https://github.com/pypa/packaging/issues/172 for the relevant recent work that improved this debug attribute detection on Windows.

wheel/src/wheel/bdist_wheel.py already has:

from .vendored.packaging import tags

...and uses tags.interpreter_name(), tags.interpreter_version(), and tags.sys_tags(). So it seems like using the tags module a little more extensively should be safe, as long as it gives the same behavior on all Python versions still supported by wheel (>=3.7 according to wheel/setup.py).

It seems to me that the local implementation of get_abi_tag() could be replaced with an appropriate call to tags.sys_tags(), and get_abi_tag() could be removed. The current code does:

            impl_name = tags.interpreter_name()
            impl_ver = tags.interpreter_version()
            impl = impl_name + impl_ver
            # We don't work on CPython 3.1, 3.0.
            if self.py_limited_api and (impl_name + impl_ver).startswith("cp3"):
                impl = self.py_limited_api
                abi_tag = "abi3"
            else:
                abi_tag = str(get_abi_tag()).lower()
            tag = (impl, abi_tag, plat_name)

...where I could imagine it instead doing:

            impl_name = tags.interpreter_name()
            impl_ver = tags.interpreter_version()
            impl = impl_name + impl_ver
            # We don't work on CPython 3.1, 3.0.
            if self.py_limited_api and (impl_name + impl_ver).startswith("cp3"):
                impl = self.py_limited_api
                abi_tag = "abi3"
                tag = (impl, abi_tag, plat_name)
            else:
                tag = tags.sys_tags()[0]

If this isn't feasible for some reason, another option would be to change the local implementation of get_abi_tag() to imitate the relevant packaging.tags._cpython_abis() code that detects the debug and with_pymalloc attributes, with a particular care not to warn on Windows in an expected situation that is immediately going to be rectified by an appropriate alternate detection mechanism. This is more complicated, so I won't attempt to suggest the exact patch for this option.

pypa / wheel

When running bdist_wheel on Windows, warning appears: "Config variable 'Py_DEBUG' is unset, Python ABI tag may be incorrect" #461