importlib: _import_module_using_spec also imports parent modules

According to the Python import implementation:

https://github.com/python/cpython/blob/73906d5c908c1e0b73c5436faeff7d93698fc074/Lib/importlib/_bootstrap.py#L1308-L1311

When we import a module we should also import its parents, and set the child as attribute of its parent.

Author: nicoddemus

src/_pytest/pathlib.py

@@ -636,31 +636,30 @@ def _import_module_using_spec(
 
     if spec_matches_module_path(spec, module_path):
         assert spec is not None
+        # Attempt to import the parent module, seems is our responsibility:
+        # https://github.com/python/cpython/blob/73906d5c908c1e0b73c5436faeff7d93698fc074/Lib/importlib/_bootstrap.py#L1308-L1311
+        parent_module_name, _, name = module_name.rpartition(".")
+        parent_module: Optional[ModuleType] = sys.modules.get(parent_module_name)
+        if parent_module is None and parent_module_name:
+            with contextlib.suppress(ModuleNotFoundError, ImportWarning):
+                parent_module = importlib.import_module(parent_module_name)
+
+        # Find spec and import this module.
         mod = importlib.util.module_from_spec(spec)
         sys.modules[module_name] = mod
         spec.loader.exec_module(mod)  # type: ignore[union-attr]
+
+        # Set this module as an attribute of the parent module (#12194).
+        if parent_module is not None:
+            setattr(parent_module, name, mod)
+
         if insert_modules:
             insert_missing_modules(sys.modules, module_name)
-        _set_name_in_parent(mod)
         return mod
 
     return None
 
 
-def _set_name_in_parent(module: ModuleType) -> None:
-    """
-    Sets an attribute in the module's parent pointing to the module itself (#12194).
-
-    Based on https://github.com/python/cpython/blob/73906d5c908c1e0b73c5436faeff7d93698fc074/Lib/importlib/_bootstrap.py#L1335-L1342.
-    """
-    parent, _, name = module.__name__.rpartition(".")
-    if not parent:
-        return
-    parent_module = sys.modules.get(parent)
-    if parent_module is not None:
-        setattr(sys.modules[parent], name, module)
-
-
 def spec_matches_module_path(
     module_spec: Optional[ModuleSpec], module_path: Path
 ) -> bool:

testing/test_pathlib.py

@@ -1127,6 +1127,41 @@ def test_safe_exists(tmp_path: Path) -> None:
 
 
 def test_import_sets_module_as_attribute(pytester: Pytester) -> None:
+    """Unittest test for #12194."""
+    pytester.path.joinpath("foo/bar/baz").mkdir(parents=True)
+    pytester.path.joinpath("foo/__init__.py").touch()
+    pytester.path.joinpath("foo/bar/__init__.py").touch()
+    pytester.path.joinpath("foo/bar/baz/__init__.py").touch()
+    pytester.syspathinsert()
+
+    # Import foo.bar.baz and ensure parent modules also ended up imported.
+    baz = import_path(
+        pytester.path.joinpath("foo/bar/baz/__init__.py"),
+        mode=ImportMode.importlib,
+        root=pytester.path,
+        consider_namespace_packages=False,
+    )
+    assert baz.__name__ == "foo.bar.baz"
+    foo = sys.modules["foo"]
+    assert foo.__name__ == "foo"
+    bar = sys.modules["foo.bar"]
+    assert bar.__name__ == "foo.bar"
+
+    # Check parent modules have an attribute pointing to their children.
+    assert bar.baz is baz
+    assert foo.bar is bar
+
+    # Ensure we returned the "foo.bar" module cached in sys.modules.
+    bar_2 = import_path(
+        pytester.path.joinpath("foo/bar/__init__.py"),
+        mode=ImportMode.importlib,
+        root=pytester.path,
+        consider_namespace_packages=False,
+    )
+    assert bar_2 is bar
+
+
+def test_import_sets_module_as_attribute_regression(pytester: Pytester) -> None:
     """Regression test for #12194."""
     pytester.path.joinpath("foo/bar/baz").mkdir(parents=True)
     pytester.path.joinpath("foo/__init__.py").touch()