How does intellisense infer the __init__ method from dataclass annotation?

[dvargas92495]

Hey everyone! Not sure where the best place was to answer this question but was hoping this was a good place to start.

I'm interested in understanding how IDEs, mypy, etc understand that a class annotated with @dataclass is able to infer what the type signature of the __init__ method of that new class is. In other words, how the signature on that appears on hover is generated (see below):

I understand how it works at runtime. From reading the source code, I see how the annotation creates an __init__ methods using exec and then attaches to the annotated class as an attribute. However, my interest is on the static analysis side. What is the key piece that allows other systems to know the type hints of __init__ dynamically?

I created a repro repo where I'm interested in replicating this behavior for another annotation. In that example, I tried copy pasting the exact source code and typeshed annotations for dataclasses.py, resolved all mypy errors that arose, switched the name from dataclass to vargas, and saw that I was still unable to get the desired end effect, as evidenced my the type: ignore needed next to the initialization of B. My end goal is discovering how to make an annotation that could generate type hints for any attribute, using whatever magic dataclass's are using under the hood.

Thanks in advance!

[dvargas92495]

Oh is this the key? https://github.com/python/mypy/blob/4554bd0c6d49506a4a1c77dcf344dca4efee92e1/mypy/plugins/dataclasses.py#L204

[dvargas92495]

Was able to unblock myself in mypy, but discovered that VSCode actually uses pyright under the hood and have taken my conversation there. Closing this for now