Improve type hints for BaseTemporalField and JSONField in forms

[01xnikhil]

I have made things!

I noticed that some fields in forms/fields.pyi were still using Any for many important attributes, which makes type-checking less effective. I have updated these to be more specific.

What I changed:
In BaseTemporalField, I changed input_formats to Collection[str] | None. This helps when passing custom date/time formats.
In JSONField, I narrowed encoder and decoder from Any to their respective json module types (type[json.JSONEncoder], etc.).
I also noticed re_decimal in IntegerField was Any, so I've updated that to Pattern[str] as well.
Added a new test file tests/assert_type/forms/test_fields.py to make sure these new types actually work with assert_type.

Testing:
Ran Mypy on the modified files and the new test case, and both returned success.

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[UnknownPlatypus]

Does this align with how we type other regex created by the django util function _lazy_re_compile ?

[01xnikhil]

Does this align with how we type other regex created by the django util function _lazy_re_compile ?

Yeah, it matches the existing patterns in the codebase. I checked django-stubs/utils/functional.pyi and saw that SimpleLazyObject is a Generic[_T]. Since _lazy_re_compile wraps the compiled pattern, using Pattern[str] | SimpleLazyObject[Pattern[str]] makes sure Mypy is happy whether the object is still lazy or already evaluated. It’s consistent with how we've handled other lazy objects here.

[UnknownPlatypus]

Looking at usage in django of _lazy_re_compile, i find these for ex that are annotated like so:

RFC1123_DATE: Pattern[str]
RFC850_DATE: Pattern[str]
ASCTIME_DATE: Pattern[str]

long_open_tag_without_closing_re: SimpleLazyObject

word_split_re: Pattern[str] | SimpleLazyObject

cc_delim_re: Any  # Any: SimpleLazyObject wrapping a compiled regex

So you proposal would be yet another way of expressing the same idea.
What is the correct version ? Can we pick one and use it in every places ?

Given the typing of _lazy_re_compile, I think we should use Pattern everywhere because it reflects the runtime behavior even if it's not 100% correct.

def _lazy_re_compile(regex: _P | Pattern[_P], flags: int = 0) -> Pattern[_P]: ...

[01xnikhil]

Looking at usage in django of _lazy_re_compile, i find these for ex that are annotated like so:

RFC1123_DATE: Pattern[str]
RFC850_DATE: Pattern[str]
ASCTIME_DATE: Pattern[str]

long_open_tag_without_closing_re: SimpleLazyObject

word_split_re: Pattern[str] | SimpleLazyObject

cc_delim_re: Any  # Any: SimpleLazyObject wrapping a compiled regex

So you proposal would be yet another way of expressing the same idea. What is the correct version ? Can we pick one and use it in every places ?

Given the typing of _lazy_re_compile, I think we should use Pattern everywhere because it reflects the runtime behavior even if it's not 100% correct.

def _lazy_re_compile(regex: _P | Pattern[_P], flags: int = 0) -> Pattern[_P]: ...

Thanks for the guidance, I totally agree—sticking with Pattern[str] for consistency makes the most sense.

I have my college minor exams until April 18th, so I will be back on the 18th evening to update the PR and standardize the other occurrences.

Thanks for understanding.

[01xnikhil]

Hello 👋 @UnknownPlatypus ,
Updated all three files to Pattern[str] as you said.
But stubtest is failing because may be these are SimpleLazyObject at runtime. Should I wrap them in SimpleLazyObject[Pattern[str]] or just add a # type: ignore for now?

Let me know what's better !