Hypothesis ≥ 6.130.13 on Python 3.9 doesn't support the LL(1) parser anymore

[the-13th-letter]

CPython 3.9 can optionally still use the older LL(1) parser (Python 3.8 and lower), instead of the newer LL(1) parser (Python 3.10 and higher). The LL(1) parser does not understand the full set of syntax legalized with Python 3.9… in particular, it cannot parse with (expr1 as expr2, expr3 as expr4) statements correctly.

As of hypothesis-python-6.130.13, the code no longer parses under the LL(1) parser. For example, using pytest and coverage in a Python 3.9 hatch environment with PYTHONOLDPARSER=1 set yields the following syntax error [non-public bits have been redacted]:

ImportError while loading conftest '.../tests/conftest.py'.
tests/__init__.py:26: in <module>
    import hypothesis
.../.local/share/hatch/env/virtual/.../lib/python3.9/site-packages/hypothesis/__init__.py:29: in <module>
    from hypothesis.core import example, find, given, reproduce_failure, seed
.../.local/share/hatch/pythons/3.9/python/lib/python3.9/ast.py:50: in parse
    return compile(source, filename, mode, flags,
E     File ".../.local/share/hatch/env/virtual/.../lib/python3.9/site-packages/hypothesis/core.py", line 1108
E       BuildContext(data, is_final=is_final) as context,
E                                             ^
E   SyntaxError: invalid syntax
.../.local/share/hatch/env/virtual/.../lib/python3.9/site-packages/coverage/inorout.py:509: CoverageWarning: Module ... was never imported. (module-not-imported)
  self.warn(f"Module {pkg} was never imported.", slug="module-not-imported")

(The same happens in a PyPy 3.9 environment with PYTHONOLDPARSER=1.)

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The issue is due to f151eec (6.130.13), which specifically refactored this snippet of code into the Py3.9/LL(1)-incompatible form, starting from the compatible form. I suggest reverting this snippet to the LL(1)-compatible form.

[Zac-HD]

I'd be happy to accept a PR reverting this, though note that we'll be dropping support for Python 3.9 in October when it reaches end of life.

[the-13th-letter]

[…] note that we'll be dropping support for Python 3.9 in October when it reaches end of life.

Assuming that the package metadata indicates as such, that's fine. But while Python 3.9 is not yet at EOL and while hypothesis still declares compatibility with Python 3.9, I'd like to ensure this compatibility assertion is reliable, and that no one¹ using the LL(1) parser need explicitly upper-bound their hypothesis installation.

Footnotes

1. As the adage goes: The sanity I'm saving may very well be my own… ↩