overloads_evaluation error

Overload union expansion failure

When a function-body call passes a union-typed argument to an overloaded function and, after expanding the union, at least one member fails to match any overload signature, Basilisk reports the error.

@overload
def example(x: int, y: str, z: int) -> str: ...
@overload
def example(x: int, y: int, z: int) -> int: ...
def example(x: int, y: int | str, z: int) -> int | str:
    return 1

def check(v: int | str) -> None:
    example(v, v, 1)  # E -- str not assignable to int in any overload

How to handle it

Every rule is on by default — strict is the default, not a cage. You can dial overloads_evaluation down per-file or per-path from your editor or pyproject.toml, or fix the code so it type-checks. See the Type System rules and the complete diagnostic reference.

Canonical URL: https://www.basilisk-python.dev/errors/overloads_evaluation