Cannot infer empty functions

[brycepg]

Steps to reproduce

import astroid
astroid.extract_node("""
def f():
    pass
f()
""").inferred()

Current behavior

raises StopIteration

Expected behavior

Returns [const.NoneType]

python -c "from astroid import __pkginfo__; print(__pkginfo__.version)" output

2.0.0

This also applies to procedural functions which don't explicitly return any values.

[PCManticore]

Makes sense.

This happens because the inference for functions looks through each return value here (https://github.com/PyCQA/astroid/blob/629c92db2dc1b016f4bf47645c95c42e65fd3bd6/astroid/scoped_nodes.py#L1558) and tries to infer the result from there. But since functions like this don't have an explicit return value, the inference gets into raise_if_nothing_inferred over here (https://github.com/PyCQA/astroid/blob/ac3e82e9bd8678086325a71a927a06bbc43d415e/astroid/decorators.py#L140), resulting in the exception you see.

[brycepg]

What should we infer for a function that always raises an exception? I don't think it should be None. Uninferable I guess?

---

I tried to add this, but It caused a cascade of errors where we are looking for Uninferable instead of const.None

[PCManticore]

@brycepg I would say it should return Uninferable, as raising exceptions is not necessarily returning a value from the function. Although we'd want some mechanism to get what exceptions a function could raise.

Regarding your last statement, you mean you added Uninferable for functions that raise exceptions or for functions that return None? Which of these failed with the cascade of errors?

[brycepg]

@PCManticore I made functions that do not have any return/yield nodes infer to None instead of Uninferable, and it broke a lot of tests.