Invalid Match Pattern

What it does

Checks for invalid match patterns.

Why is this bad?

Invalid match patterns can cause a TypeError at runtime. This includes:

• Using a non-type object in a class pattern.
• Providing positional subpatterns when __match_args__ is missing or has an invalid static type.
• Matching against collections.abc.Callable with positional subpatterns.
• Matching against a non-runtime-checkable protocol.
• Matching against a TypedDict.

Examples

class Point:
    __match_args__ = ("x", "y")


def describe(p: Point) -> None:
    match p:
        # TypeError at runtime: Point() accepts 2 positional sub-patterns (3 given)
        case Point(x, y, z):  # error: [invalid-match-pattern]
            ...

NotAClass = 42

match object():
    # TypeError at runtime: called match pattern must be a class
    case NotAClass():  # error: [invalid-match-pattern]
        ...