gh-86298: Ensure that __loader__ and __spec__.loader agree in warnings.warn_explicit()

Doc/reference/import.rst

@@ -558,6 +558,11 @@ listed below.
  It is **strongly** recommended that you rely on :attr:`__spec__`
  instead instead of this attribute.
 
+ .. versionchanged:: 3.12
+ The value of ``__loader__`` is expected to be the same as
+ ``__spec__.loader``. The use of ``__loader__`` is deprecated and slated
+ for removal in Python 3.14.
+
 .. attribute:: __package__
 
  The module's ``__package__`` attribute may be set. Its value must
@@ -568,6 +573,9 @@ listed below.
  submodules, to the parent package's name. See :pep:`366` for further
  details.
 
+ This attribute is used instead of ``__name__`` to calculate explicit
+ relative imports for main modules, as defined in :pep:`366`.
+
  It is **strongly** recommended that you rely on :attr:`__spec__`
  instead instead of this attribute.
 

Lib/importlib/_bootstrap_external.py

@@ -862,6 +862,54 @@ def spec_from_file_location(name, location=None, *, loader=None,
  return spec
 
 
+def _bless_my_loader(module_globals):
+ """Helper function for _warnings.c
+
+ See GH#97850 for details.
+ """
+ # 2022-10-06(warsaw): For now, this helper is only used in _warnings.c and
+ # that use case only has the module globals. This function could be
+ # extended to accept either that or a module object. However, in the
+ # latter case, it would be better to raise certain exceptions when looking
+ # at a module, which should have either a __loader__ or __spec__.loader.
+ # For backward compatibility, it is possible that we'll get an empty
+ # dictionary for the module globals, and that cannot raise an exception.
+ if not isinstance(module_globals, dict):
+ return None
+
+ missing = object()
+ loader = module_globals.get('__loader__', None)
+ spec = module_globals.get('__spec__', missing)
+
+ if loader is None:
+ if spec is missing:
+ # If working with a module:
+ # raise AttributeError('Module globals is missing a __spec__')
+ return None
+ elif spec is None:
+ raise ValueError('Module globals is missing a __spec__.loader')
+
+ spec_loader = getattr(spec, 'loader', missing)
+
+ if spec_loader in (missing, None):
+ if loader is None:
+ exc = AttributeError if spec_loader is missing else ValueError
+ raise exc('Module globals is missing a __spec__.loader')
+ _warnings.warn(
+ 'Module globals is missing a __spec__.loader',
+ DeprecationWarning)
+ spec_loader = loader
+
+ assert spec_loader is not None
+ if loader is not None and loader != spec_loader:
+ _warnings.warn(
+ 'Module globals; __loader__ != __spec__.loader',
+ DeprecationWarning)
+ return loader
+
+ return spec_loader
+
+
 # Loaders #####################################################################
 
 class WindowsRegistryFinder:

Lib/test/test_importlib/import_/test_helpers.py

@@ -2,7 +2,9 @@
 
 from importlib import _bootstrap_external, machinery
 import os.path
+from types import ModuleType, SimpleNamespace
 import unittest
+import warnings
 
 from .. import util
 
@@ -67,5 +69,116 @@ def test_no_loader_no_spec_but_source(self):
 
 FrozenFixUpModuleTests, SourceFixUpModuleTests = util.test_both(FixUpModuleTests)
 
+
+class TestBlessMyLoader(unittest.TestCase):
+ # GH#86298 is part of the migration away from module attributes and toward
+ # __spec__ attributes. There are several cases to test here. This will
+ # have to change in Python 3.14 when we actually remove/ignore __loader__
+ # in favor of requiring __spec__.loader.
+
+ def test_gh86298_no_loader_and_no_spec(self):
+ bar = ModuleType('bar')
+ del bar.__loader__
+ del bar.__spec__
+ # 2022-10-06(warsaw): For backward compatibility with the
+ # implementation in _warnings.c, this can't raise an
+ # AttributeError. See _bless_my_loader() in _bootstrap_external.py
+ # If working with a module:
+ ## self.assertRaises(
+ ## AttributeError, _bootstrap_external._bless_my_loader,
+ ## bar.__dict__)
+ self.assertIsNone(_bootstrap_external._bless_my_loader(bar.__dict__))
+
+ def test_gh86298_loader_is_none_and_no_spec(self):
+ bar = ModuleType('bar')
+ bar.__loader__ = None
+ del bar.__spec__
+ # 2022-10-06(warsaw): For backward compatibility with the
+ # implementation in _warnings.c, this can't raise an
+ # AttributeError. See _bless_my_loader() in _bootstrap_external.py
+ # If working with a module:
+ ## self.assertRaises(
+ ## AttributeError, _bootstrap_external._bless_my_loader,
+ ## bar.__dict__)
+ self.assertIsNone(_bootstrap_external._bless_my_loader(bar.__dict__))
+
+ def test_gh86298_no_loader_and_spec_is_none(self):
+ bar = ModuleType('bar')
+ del bar.__loader__
+ bar.__spec__ = None
+ self.assertRaises(
+ ValueError,
+ _bootstrap_external._bless_my_loader, bar.__dict__)
+
+ def test_gh86298_loader_is_none_and_spec_is_none(self):
+ bar = ModuleType('bar')
+ bar.__loader__ = None
+ bar.__spec__ = None
+ self.assertRaises(
+ ValueError,
+ _bootstrap_external._bless_my_loader, bar.__dict__)
+
+ def test_gh86298_loader_is_none_and_spec_loader_is_none(self):
+ bar = ModuleType('bar')
+ bar.__loader__ = None
+ bar.__spec__ = SimpleNamespace(loader=None)
+ self.assertRaises(
+ ValueError,
+ _bootstrap_external._bless_my_loader, bar.__dict__)
+
+ def test_gh86298_no_spec(self):
+ bar = ModuleType('bar')
+ bar.__loader__ = object()
+ del bar.__spec__
+ with warnings.catch_warnings():
+ self.assertWarns(
+ DeprecationWarning,
+ _bootstrap_external._bless_my_loader, bar.__dict__)
+
+ def test_gh86298_spec_is_none(self):
+ bar = ModuleType('bar')
+ bar.__loader__ = object()
+ bar.__spec__ = None
+ with warnings.catch_warnings():
+ self.assertWarns(
+ DeprecationWarning,
+ _bootstrap_external._bless_my_loader, bar.__dict__)
+
+ def test_gh86298_no_spec_loader(self):
+ bar = ModuleType('bar')
+ bar.__loader__ = object()
+ bar.__spec__ = SimpleNamespace()
+ with warnings.catch_warnings():
+ self.assertWarns(
+ DeprecationWarning,
+ _bootstrap_external._bless_my_loader, bar.__dict__)
+
+ def test_gh86298_loader_and_spec_loader_disagree(self):
+ bar = ModuleType('bar')
+ bar.__loader__ = object()
+ bar.__spec__ = SimpleNamespace(loader=object())
+ with warnings.catch_warnings():
+ self.assertWarns(
+ DeprecationWarning,
+ _bootstrap_external._bless_my_loader, bar.__dict__)
+
+ def test_gh86298_no_loader_and_no_spec_loader(self):
+ bar = ModuleType('bar')
+ del bar.__loader__
+ bar.__spec__ = SimpleNamespace()
+ self.assertRaises(
+ AttributeError,
+ _bootstrap_external._bless_my_loader, bar.__dict__)
+
+ def test_gh86298_no_loader_with_spec_loader_okay(self):
+ bar = ModuleType('bar')
+ del bar.__loader__
+ loader = object()
+ bar.__spec__ = SimpleNamespace(loader=loader)
+ self.assertEqual(
+ _bootstrap_external._bless_my_loader(bar.__dict__),
+ loader)
+
+
 if __name__ == "__main__":
  unittest.main()

Misc/NEWS.d/next/Core and Builtins/2022-10-04-14-04-40.gh-issue-86298.QVM7G1.rst

@@ -0,0 +1,3 @@
+In cases where ``warnings.warn_explicit()`` consults the module's loader, an
+``DeprecationWarning`` is issued when ``m.__loader__`` differs from
+``m.__spec__.loader``.

Python/_warnings.c

@@ -977,19 +977,26 @@ warnings_warn_impl(PyObject *module, PyObject *message, PyObject *category,
 static PyObject *
 get_source_line(PyInterpreterState *interp, PyObject *module_globals, int lineno)
 {
+ PyObject *external;
  PyObject *loader;
  PyObject *module_name;
  PyObject *get_source;
  PyObject *source;
  PyObject *source_list;
  PyObject *source_line;
 
- /* Check/get the requisite pieces needed for the loader. */
- loader = _PyDict_GetItemWithError(module_globals, &_Py_ID(__loader__));
+ /* stolen from import.c */
+ external = PyObject_GetAttrString(interp->importlib, "_bootstrap_external");
+ if (external == NULL) {
+ return NULL;
+ }
+
+ loader = PyObject_CallMethod(external, "_bless_my_loader", "O", module_globals, NULL);
+ Py_DECREF(external);
  if (loader == NULL) {
  return NULL;
  }
- Py_INCREF(loader);
+
  module_name = _PyDict_GetItemWithError(module_globals, &_Py_ID(__name__));
  if (!module_name) {
  Py_DECREF(loader);