type annotations for Config allow mismatched default type

[chdsbd]

With the current type stubs, it's possible to specify a default of a different type from the cast type. In some cases this works (int cast with a bool default), in other cases it doesn't (int cast with a str default).

Additionally, this type annotation isn't supported by mypy:

BOOL_DEFAULT_STR = config("BOOL_DEFAULT_STR", cast=bool, default="true")
reveal_type(BOOL_DEFAULT_STR) # Revealed type is "builtins.list[builtins.object]"mypy(note)

I suggest we make the types more strict to disallow this error case, at the cost of disallowing the valid use case of an int cast with a bool default.

from starlette.config import Config

config = Config()
# valid. Default converts to 1
INT_WITH_BOOL_DEFAULT = config("INT_WITH_BOOL_DEFAULT", cast=int, default=True)
INT_WITH_STR_DEFAULT = config("INT_WITH_BOOL_DEFAULT", cast=int, default="True")


# >>> INT_WITH_STR_DEFAULT = config("INT_WITH_BOOL_DEFAULT", cast=int, default="True")
# Traceback (most recent call last):
#   File "/Users/christopherdignam/projects/starlette/starlette/config.py", line 146, in _perform_cast
#     return cast(value)
# ValueError: invalid literal for int() with base 10: 'True'

# During handling of the above exception, another exception occurred:

# Traceback (most recent call last):
#   File "<stdin>", line 1, in <module>
#   File "/Users/christopherdignam/projects/starlette/starlette/config.py", line 102, in __call__
#     return self.get(key, cast, default)
#   File "/Users/christopherdignam/projects/starlette/starlette/config.py", line 117, in get
#     return self._perform_cast(key, default, cast)
#   File "/Users/christopherdignam/projects/starlette/starlette/config.py", line 148, in _perform_cast
#     raise ValueError(
# ValueError: Config 'INT_WITH_BOOL_DEFAULT' has value 'True'. Not a valid int.

Would a PR be accepted that made the type stricter to disallow both of these examples?

[Kludex]

Yes. PR is welcome.

[Kludex]

btw, I couldn't find you anywhere, now I just did... @chdsbd Thanks for sponsoring me! ❤️