fix Pydantic lax-mode rewrites Pattern[str] to Pattern[LaxStr] and rejects re.Pattern[str] #2991

[asukaminato0721]

Summary

Fixes #2991

Pydantic lax conversion now special-cases regex patterns so re.Pattern[T] expands to re.Pattern[T] | T instead of recursively widening the inner type to LaxStr.

Test Plan

add test

[Copilot]

Pull request overview

Fixes Pyrefly’s Pydantic lax-mode type expansion for regex patterns so that re.Pattern[T] (and typing.Pattern[T]) accepts both a compiled pattern and the underlying input type T, without recursively widening T (e.g., avoiding Pattern[LaxStr]).

Changes:

• Add a dedicated lax-mode conversion path for regex Pattern types to produce Pattern[T] | T.
• Add a regression test asserting correct __init__ signature and acceptance/rejection behavior for re.Pattern[str] fields.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
pyrefly/lib/alt/class/pydantic_lax.rs	Special-cases re.Pattern/typing.Pattern during lax expansion to union the pattern type with its type argument.
pyrefly/lib/test/pydantic/strictness.rs	Adds a testcase covering re.Pattern[str] lax-mode initialization and rejects bytes input.

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[github-actions]

According to mypy_primer, this change doesn't affect type check results on a corpus of open source code. ✅

[meta-codesync]

@stroxler has imported this pull request. If you are a Meta employee, you can view this in D100036927.

[migeed-z]

Review automatically exported from Phabricator review in Meta.

[meta-codesync]

@stroxler merged this pull request in c12e9d6.