Conditional deduction support with comparison of `sys.hexversion` against integer literal

Feature

Currently, mypy statically evaluates some if branches involving only sys.version_info and sys.platform as always false based on the version and platform it is running on. I propose to have it recognize comparisons against sys.hexversion as well.

Pitch

Some specialized functions targeting bugs patched in a certain alpha, beta or release candidate or internal behavioural differences between patch versions would need this functionality. Also, it may be desirable to give alpha/beta/rc versions a grace period for certain small deprecations, only raising an error on their use in the final python release. Implementation-wise, because the exact value of hexversion can be easily retrieved, and sys.platform and sys.version_info have set precedents, I do not believe it would be unreasonably hard to implement.

Commencez par localiser l’évaluation statique existante de mypy pour les conditions impliquant sys.version_info et sys.platform. Suivez la manière dont les comparaisons de versions sont représentées et testées, puis déterminez le comportement attendu pour les comparaisons entre sys.hexversion et des littéraux entiers. Le travail sera considéré comme terminé lorsque les conditions hexversion prises en charge seront évaluées de manière cohérente avec les cas existants et que des tests couvriront les comparaisons demandées.