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## Summary For a type alias like the one below, where `UnknownClass` is something with a dynamic type, we previously lost track of the fact that this dynamic type was explicitly specialized *with a type variable*. If that alias is then later explicitly specialized itself (`MyAlias[int]`), we would miscount the number of legacy type variables and emit a `invalid-type-arguments` diagnostic ([playground](https://play.ty.dev/886ae6cc-86c3-4304-a365-510d29211f85)). ```py T = TypeVar("T") MyAlias: TypeAlias = UnknownClass[T] | None ``` The solution implemented here is not pretty, but we can hopefully get rid of it via https://github.com/astral-sh/ty/issues/1711. Also, once we properly support `ParamSpec` and `Concatenate`, we should be able to remove some of this code. This addresses many of the `invalid-type-arguments` false-positives in https://github.com/astral-sh/ty/issues/1685. With this change, there are still some diagnostics of this type left. Instead of implementing even more (rather sophisticated) workarounds for these cases as well, it might be much easier to wait for full `ParamSpec`/`Concatenate` support and then try again. A disadvantage of this implementation is that we lose track of some `@Todo` types and replace them with `Unknown`. We could spend more effort and try to preserve them, but I'm unsure if this is the best use of our time right now. ## Test Plan New Markdown tests.
Markdown files within the mdtest/ subdirectory are tests of type inference and type checking;
executed by the tests/mdtest.rs integration test.
See crates/ty_test/README.md for documentation of this test format.