tuple[Literal[1, 2]] is not assignable to tuple[Literal[1]] | tuple[Literal[2]]

[InSyncWithFoo]

Reproducible example (playground):

from typing import Literal

def f1(x: tuple[Literal[1, 2]]) -> tuple[Literal[1]] | tuple[Literal[2]]:
    return x  # error: "tuple[Literal[1, 2]]" is incompatible with "tuple[Literal[1]] | tuple[Literal[2]]"

tuple[] should distribute over the union Literal[1, 2]/Literal[1] | Literal[2], resulting in tuple[Literal[1]] | tuple[Literal[2]]. Is this a bug or a known limitation?

[erictraut]

This is a known limitation. Pyright does not expand tuples when considering type compatibility. No other Python type checkers do this either.

Pyright, unlike other type checkers, does perform limited tuple expansion for purposes of type narrowing in match statements, but that's the only place where such expansion is performed currently.

The typing spec was recently updated to indicate that such types are equivalent. It indicates that type checkers may treat them as such for purposes of narrowing tuple types, but it doesn't mandate it.