[ty] Reject type[Callable] special form

[charliermarsh]

Summary

The typing spec says:

Any other special forms like Callable are not allowed as an argument to type.

We already reject Generic and TypedDict. We should probably also reject Literal. But this PR adds Callable.

Closes astral-sh/ty#2964.

[astral-sh-bot]

Typing conformance results

No changes detected ✅

Current numbers

The percentage of diagnostics emitted that were expected errors held steady at 87.07%. The percentage of expected errors that received a diagnostic held steady at 77.62%.

[astral-sh-bot]

mypy_primer results

No ecosystem changes detected ✅

[astral-sh-bot]

Memory usage report

Memory usage unchanged ✅

[carljm]

Thanks! Would be great to just clear out all these todo types with tighter validation instead (in separate PRs). It might reveal missing cases we should handle. If those are bigger features, they can remain more narrowly focused todo types.

[carljm]

By not calling self.infer_type_expression(parameters) here (as the catch-all below does) we regress in missing out on some actionable nested diagnostics, e.g. in a case like type[Callable[..., Missing]] or a malformed Callable type expression inside type[].

[KotlinIsland]

Any other special forms like Callable are not allowed as an argument to type.

Callable isn't a special form though, it's a normal class. i think this is a spec issue

[carljm]

@KotlinIsland Every type checker treats it as a special form, and typeshed defines it that way. Let's not debate that here. If you want to propose a spec change, go ahead, and we can discuss in the Discuss thread for that proposed change.