Error in type comment points to wrong line

[JukkaL]

This fragment generates an error on the line @deco which is confusing:

def deco(x): return x

@deco   # Error: Name 'bad' is not defined
def f(y):
    # type: (bad) -> None
    pass

[emmatyping]

This is an instance of #3871. I tested on 3.8 and with the better source information, it was able to correctly report the error on the function declaration line.

Perhaps we should document this?

[ilevkivskyi]

Perhaps we should document this?

It probably makes sense to add a short item in Common issues explaining that type errors may rarely appear in strange locations, and # type: ignore must be placed exactly there.

[JukkaL]

Even in 3.8 the error points to the line def f(y):, but it would be better if we can somehow make it point to the type comment line. This may require some hacks if the AST doesn't contain information about the line of the type comment, but it may be worth it.

[AlexWaygood]

I'm changing the priority to "low", since type comments are rarely used in modern Python (parameter and variable annotations are generally preferred).

[JelleZijlstra]

Maybe we should just deprecate type comment support.

[emmatyping]

I believe type comments are part of PEP 484 so they would need to be deprecated and removed as part of the PEP, there is also the consideration of for/with statements, I've opened a new thread on typing-sig about this https://mail.python.org/archives/list/[email protected]/thread/66JDHQ2I3U3CPUIYA43W7SPEJLLPUETG/

[hauntsaninja]

This isn't worth fixing