importlib: set module as attribute in its parent module

This needs to be done manually, not being done as part of the import mechanism:

https://github.com/python/cpython/blob/73906d5c908c1e0b73c5436faeff7d93698fc074/Lib/importlib/_bootstrap.py#L1335-L1342

Fix pytest-dev#12194

changelog/12194.bugfix.rst

@@ -0,0 +1 @@
+Fixed a bug with ``--importmode=importlib`` and ``--doctest-modules`` where child modules did not appear as attributes in parent modules.

src/_pytest/pathlib.py

@@ -641,11 +641,26 @@ def _import_module_using_spec(
         spec.loader.exec_module(mod)  # type: ignore[union-attr]
         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

@@ -1126,6 +1126,31 @@ def test_safe_exists(tmp_path: Path) -> None:
         assert safe_exists(p) is False
 
 
+def test_import_sets_module_as_attribute(pytester: Pytester) -> None:
+    """Regression 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()
+    f = pytester.makepyfile(
+        """
+        import foo
+        from foo.bar import baz
+        foo.bar.baz
+
+        def test_foo() -> None:
+            pass
+        """
+    )
+
+    pytester.syspathinsert()
+    result = pytester.runpython(f)
+    assert result.ret == 0
+
+    result = pytester.runpytest("--import-mode=importlib", "--doctest-modules")
+    assert result.ret == 0
+
+
 class TestNamespacePackages:
     """Test import_path support when importing from properly namespace packages."""