mypy CSTTypedTransformerFunctions issue

[zhammer]

context

ran into a peculiar bug where the CSTTypedTransformerFunctions types seem to not work with mypy. leave_{Node} calls fail mypy type check with Signature of "leave_{Node}" is incompatible with supertype "CSTTypedTransformerFunctions".

the type definition that mypy says is incompatible doesnt look incompatible to me, though:

LibCST/libcst/_typed_visitor.py

Lines 5785 to 5787 in c9b10fe

	@mark_no_op
	def leave_Module(self, original_node: "Module", updated_node: "Module") -> "Module":
	return updated_node

i'm not sure yet if this is an issue with mypy or libcst, but wanted to share here for replication. (mypy's error messages aren't super descriptive so am still trying to figure out where mypy is getting the incompatible defintion from.)

replicate (using: python 3.7.5)

./requirements.txt

libcst==0.2.4
mypy==0.750

./transformer.py

import libcst

class Transformer(libcst.CSTTransformer):

    def leave_Module(self, original_node: libcst.Module, updated_node: libcst.Module) -> libcst.Module:
        return updated_node

    def leave_Call(self, original_node: libcst.Call, updated_node: libcst.Call) -> libcst.Call:
        return updated_node

mypy errors

$ mypy transformer.py 
transformer.py:5: error: Signature of "leave_Module" incompatible with supertype "CSTTypedTransformerFunctions"
transformer.py:8: error: Signature of "leave_Call" incompatible with supertype "CSTTypedTransformerFunctions"
Found 2 errors in 1 file (checked 1 source file)