[syntax-errors] Document behavior of `global` declarations in `try` nodes before 3.13 (#17285)
Summary
--
This PR extends the documentation of the `LoadBeforeGlobalDeclaration`
check to specify the behavior on versions of Python before 3.13. Namely,
on Python 3.12, the `else` clause of a `try` statement is visited before
the `except` handlers:
```pycon
Python 3.12.9 (main, Feb 12 2025, 14:50:50) [Clang 19.1.6 ] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> a = 10
>>> def g():
... try:
... 1 / 0
... except:
... a = 1
... else:
... global a
...
>>> def f():
... try:
... pass
... except:
... global a
... else:
... print(a)
...
File "<stdin>", line 5
SyntaxError: name 'a' is used prior to global declaration
```
The order is swapped on 3.13 (see
[CPython#111123](https://github.com/python/cpython/issues/111123)):
```pycon
Python 3.13.2 (main, Feb 5 2025, 08:05:21) [GCC 14.2.1 20250128] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> a = 10
... def g():
... try:
... 1 / 0
... except:
... a = 1
... else:
... global a
...
File "<python-input-0>", line 8
global a
^^^^^^^^
SyntaxError: name 'a' is assigned to before global declaration
>>> def f():
... try:
... pass
... except:
... global a
... else:
... print(a)
...
>>>
```
The current implementation of PLE0118 is correct for 3.13 but not 3.12:
[playground](https://play.ruff.rs/d7467ea6-f546-4a76-828f-8e6b800694c9)
(it flags the first case regardless of Python version).
We decided to maintain this incorrect diagnostic for Python versions
before 3.13 because the pre-3.13 behavior is very unintuitive and
confirmed to be a bug, although the bug fix was not backported to
earlier versions. This can lead to false positives and false negatives
for pre-3.13 code, but we also expect that to be very rare, as
demonstrated by the ecosystem check (before the version-dependent check
was reverted here).
Test Plan
--
N/a
ruff
2fbc4d57 - [syntax-errors] Document behavior of `global` declarations in `try` nodes before 3.13 (#17285)
