(where "not otherwise typecheckable" means types that can't be expressed with stubs - e.g., Django, dataclasses pre-PEP-681, pytest fixtures, etc.)
(It's also more difficult to support plugins effectively in a type checker like ty, than in a linter like ruff, since any non-trivial use case would likely require deep changes to how we represent types and how we implement type inference. That's not something that lends itself to a couple of simple hook extension points.)
Considering how fast uv and ruff took off, I am sure you are aware of the impact your project could have. I understand that supporting plugins is hard. However, if you are considering adding support for some popular libraries, IMHO, it would be really beneficial for the community if you could evaluate the feasibility of implementing things in a somewhat generic way, which could be then maybe leveraged by third-party authors.
In any case, thanks for all the amazing work.
I don’t have any such experience (short of a macro system, which requires code generation or runtime support) and it always makes me curious when people ask for type system plugins whether this is a standard feature in a type system I’ve never used.
So if we were to do this for ty, we would have to carefully design the internal data types and algorithms that we use to model Python code, so that they're extensible in a robust way.
But we would also have to decide what kind of Rust plugin architecture to use. (Embed a Lua interpreter? dlopen plugins at runtime? Sidecar process communication over stdin/stdout?)
Solvable problems, to be sure, but it adds to the amount of work that's needed to support this well — which in turn affects our decisions about whether/when to prioritize this relative to other features.
Regarding type checkers: while I don't love optimizing code just to make them run faster, most Python patterns can be implemented in statically checkable ways without much compromise. The benefits typically outweigh the costs. Python's dynamic features are powerful but rarely essential for everyday tasks.