fix AttributeError crash when using --import-mode=importlib

[dongfangtianyu]

closes #13026 .

• Include new tests or update existing tests when applicable.
• Allow maintainers to push and squash when merging my commits.
• Create a new changelog file in the changelog folder.

Only parent modules with the __path__ attribute can be used by the find_spec function, and most of the standard library does not meet this condition.

https://github.com/python/cpython/blob/3.9/Lib/importlib/_bootstrap_external.py#L1223

   def _find_parent_path_names(self):
        """Returns a tuple of (parent-module-name, parent-path-attr-name)"""
        parent, dot, me = self._name.rpartition('.')
        if dot == '':
            # This is a top-level module. sys.path contains the parent path.
            return 'sys', 'path'
        # Not a top-level module. parent-module.__path__ contains the
        #  parent path.
        return parent, '__path__'

So this PR adds a condition check.

[nicoddemus]

Thanks @dongfangtianyu for investigating it and opening a fix so quickly!

Left some small comments, can you take a look?

[nicoddemus]

Thanks!

[patchback]

Backport to 8.3.x: 💚 backport PR created

✅ Backport PR branch: patchback/backports/8.3.x/8cff12865691b14b4bce70e0e304524619be385d/pr-13029

Backported as #13037

🤖 @patchback
I'm built with octomachinery and
my source is open — https://github.com/sanitizers/patchback-github-app.

[manueljacob]

This is very dangerous, as it will override an already imported module if it’s not a package (i.e. lacks the __path__ attribute).

For example:

pyproject.toml:

[build-system]
requires = ["setuptools"]
build-backend = "setuptools.build_meta"

[project]
name = "foo"
version = "0.0"

[tool.setuptools.packages.find]
where = ["code"]

[tool.pytest.ini_options]
addopts = [
    "--import-mode=importlib",
]

code/foo/__init__.py:

code/foo/repl.py:

def compile_command(source):
    from code import compile_command

    return compile_command(source)

code/foo/test/test_foo.py:

from foo.repl import compile_command


def test_foo():
    assert compile_command("42") is not None

Running pytest fails with:

    def test_foo():
>       assert compile_command("42") is not None
               ^^^^^^^^^^^^^^^^^^^^^

code/foo/test/test_foo.py:6: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

source = '42'

    def compile_command(source):
>       from code import compile_command
E       ImportError: cannot import name 'compile_command' from 'code' (unknown location)

code/foo/repl.py:5: ImportError

A shorter, but more artificial example:

time/test.py:

def test():
    from time import time

    assert time() > 0

Running pytest --rootdir=. --import-mode=importlib time/test.py fails with:

    def test():
>       from time import time
E       ImportError: cannot import name 'time' from 'time' (unknown location)

time/test.py:2: ImportError