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gh-86298: Ensure that __loader__ and __spec__.loader agree in warnings.warn_explicit() (GH-97803)

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In `_warnings.c`, in the C equivalent of `warnings.warn_explicit()`, if the module globals are given (and not None), the warning will attempt to get the source line for the issued warning.  To do this, it needs the module's loader.

Previously, it would only look up `__loader__` in the module globals.  In https://github.com/python/cpython/issues/86298 we want to defer to the `__spec__.loader` if available.

The first step on this journey is to check that `loader == __spec__.loader` and issue another warning if it is not.  This commit does that.

Since this is a PoC, only manual testing for now.

```python
# /tmp/foo.py
import warnings

import bar

warnings.warn_explicit(
    'warning!',
    RuntimeWarning,
    'bar.py', 2,
    module='bar knee',
    module_globals=bar.__dict__,
    )
```

```python
# /tmp/bar.py
import sys
import os
import pathlib

# __loader__ = pathlib.Path()
```

Then running this: `./python.exe -Wdefault /tmp/foo.py`

Produces:

```
bar.py:2: RuntimeWarning: warning!
  import os
```

Uncomment the `__loader__ = ` line in `bar.py` and try it again:

```
sys:1: ImportWarning: Module bar; __loader__ != __spec__.loader (<_frozen_importlib_external.SourceFileLoader object at 0x109f7dfa0> != PosixPath('.'))
bar.py:2: RuntimeWarning: warning!
  import os
```

Automerge-Triggered-By: GH:warsaw
This commit is contained in:
Barry Warsaw 2022-10-06 19:32:53 -07:00 • committed by GitHub
parent 27369ef56f
commit 13d4489142
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8
Doc/reference/import.rst
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@ -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.