`omit_defaults` does not omit tuples and frozensets about msgspec

[jcrist]

Thanks for opening this - this should be fixed by #653. Note that for these cases specifying the default value by value (rather than via default_factory) already works:

import msgspec


class Backpack(msgspec.Struct, omit_defaults=True):
    a_list: list[str] = []
    a_tuple: tuple[str, ...] = ()
    a_frozenset: frozenset[str] = frozenset()


instance = Backpack()
print(msgspec.json.encode(instance))
#> b'{}'

The reason tuple and frozenset are the special cases here is that they're both immutable types and may always be specified by value. Since there's no functional reason to use a default_factory for these types, we hadn't implemented the logic to check for equivalent defaults based on default_factory for tuple/frozenset.

[jodal]

Thank you for the very swift fix! Especially useful with the tip on how to achieve this without waiting for a new release :-)