d6dcc377f7
## Summary Currently our `Type::Callable` wraps a four-variant `CallableType` enum. But as time has gone on, I think we've found that the four variants in `CallableType` are really more different to each other than they are similar to each other: - `GeneralCallableType` is a structural type describing all callable types with a certain signature, but the other three types are "literal types", more similar to the `FunctionLiteral` variant - `GeneralCallableType` is not a singleton or a single-valued type, but the other three are all single-valued types (`WrapperDescriptorDunderGet` is even a singleton type) - `GeneralCallableType` has (or should have) ambiguous truthiness, but all possible inhabitants of the other three types are always truthy. - As a structural type, `GeneralCallableType` can contain inner unions and intersections that must be sorted in some contexts in our internal model, but this is not true for the other three variants. This PR flattens `Type::Callable` into four distinct `Type::` variants. In the process, it fixes a number of latent bugs that were concealed by the current architecture but are laid bare by the refactor. Unit tests for these bugs are included in the PR.
Markdown files within the mdtest/ subdirectory are tests of type inference and type checking;
executed by the tests/mdtest.rs integration test.
See crates/red_knot_test/README.md for documentation of this test format.