str not compatible with StrOrLiteralStr

[solaluset]

Bug Report

mypy doesn't accept str for StrOrLiteralStr

To Reproduce

from string import Formatter
from typing import Iterable, Tuple

class MyFormatter(Formatter):
    def parse(self, s: str) -> Iterable[Tuple[str, str, str, str]]:
        for text, field, spec, conversion in super().parse(s):
            yield "a", "b", "c", "d"

(playground)

Actual Behavior

error: Return type "Iterable[tuple[str, str, str, str]]" of "parse" incompatible with return type "Iterable[tuple[StrOrLiteralStr, StrOrLiteralStr | None, StrOrLiteralStr | None, StrOrLiteralStr | None]]" in supertype "Formatter" [override]

Details

I've asked a question on SO about this and didn't get an answer (yet). As indicated in the comments:

this code passes type checking in mypy 0.971, and fails in mypy 0.981 through 1.5.0

Perhaps it's related to mypy lack of support for LiteralStr #12554

[erictraut]

The error is because you're overriding the Formatter.parse method in an incompatible way. The Formatter base class defines the return type using a constrained TypeVar and includes unions with None, but your override does not. Your override also uses an incompatible parameter name (s versus format_string) and parameter type.

[solaluset]

Perhaps you're right about TypeVar - this code passes the check:

from string import Formatter
from typing import Iterable, Tuple, TypeVar

Str = TypeVar("Str", str, str)

class MyFormatter(Formatter):
    def parse(self, s: Str) -> Iterable[Tuple[Str, Str, Str, Str]]:
        for text, field, spec, conversion in super().parse(s):
            yield "a", "b", "c", "d"

However, why doesn't mypy display error about argument type in the first example? It's also StrOrLiteralStr in the superclass.

And, more importantly, where can I get (import?) StrOrLiteralStr? StrOrLiteralStr = TypeVar("StrOrLiteralStr", str, str) doesn't look like a clean solution in my opinion.