Report oversized regex repeat count as invalid instead of crashing

[vineethsaivs]

The regex format checker is declared with raises=re.error:

@_checks_drafts(name="regex", raises=re.error)
def is_regex(instance: object) -> bool:
    if not isinstance(instance, str):
        return True
    return bool(re.compile(instance))

FormatChecker.check only converts the declared exception(s) into a FormatError. But re.compile raises OverflowError (which is not an re.error subclass) when a repetition count is too large, e.g. re.compile("a{99999999999999}"). That OverflowError escapes uncaught, so a regex-format check on such a string crashes instead of reporting it as an invalid regex, unlike every other malformed pattern (which raises re.error and is caught).

>>> from jsonschema import FormatChecker
>>> fc = FormatChecker()
>>> fc.conforms("[unterminated", "regex")   # re.error -> caught
False
>>> fc.conforms("a{99999999999999}", "regex")   # OverflowError -> escapes
Traceback (most recent call last):
  ...
OverflowError: the repetition number is too large

The same escape happens through iter_errors/validate when format checking is enabled.

Fix

Declare the checker with raises=(re.error, OverflowError) so the oversized-repeat case is reported as an invalid regex like the rest. This matches sibling checkers that already pass exception tuples (e.g. raises=(idna.IDNAError, UnicodeError)). No behavior change for valid patterns or for re.error cases.

Tests

Added TestFormatChecker.test_regex_format_rejects_overflowing_repeat_count, mirroring the existing test_format_checkers_come_with_defaults (uses checker.check(...) + assertRaises(FormatError)).

• Before: the new test errors with an uncaught OverflowError.
• After: it passes; conforms("a{99999999999999}", "regex") returns False, while conforms("[unterminated", "regex") stays False and conforms("valid.*regex", "regex") stays True.
• python -m pytest jsonschema/tests/test_format.py -> 9 passed.

Added a CHANGELOG entry.

[read-the-docs-community]

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