B030 doesn't allow splatted exceptions

[samueljsb]

I think there's a false-report coming from B030 where we have some exceptions types defined in a constant. A minimal example:

EXCEPTIONS_TO_IGNORE = (
    ValueError,
    TypeError,
)

try:
    pass
except (SyntaxError, *EXCEPTIONS_TO_IGNORE):
    pass

$ flake8 t.py
t.py:8:1: B030 Except handlers should only be names of exception classes

This isn't incorrect, so I don't think the intention of B030 is to stop this kind of thing.

versions etc

I'm using Macos 13.1, we're also seeing this in CI using Ubuntu 20.04.5.

$ python --version --version
Python 3.10.8 (main, Oct 13 2022, 10:17:43) [Clang 14.0.0 (clang-1400.0.29.102)]

$ flake8 --version
6.0.0 (flake8-bugbear: 23.2.13, mccabe: 0.7.0, pycodestyle: 2.10.0, pyflakes: 3.0.1) CPython 3.10.8 on Darwin

[samueljsb]

It also doesn't allow function calls:

def exceptions_to_ignore():
    return (ValueError, TypeError)

try:
    pass
except exceptions_to_ignore():
    pass

$ flake8 t.py
t.py:6:1: B030 Except handlers should only be names of exception classes

Whether or not this is a good way to write code or not is an open question, but should it be disallowed?

[jakkdl]

flake8-bugbear/bugbear.py

Lines 336 to 340 in fa49539

	for handler in handlers:
	if isinstance(handler, (ast.Name, ast.Attribute)):
	good_handlers.append(handler)
	else:
	bad_handlers.append(handler)

is the current logic.
Starred expressions seems reasonable to allow, and function calls are probably intentional too? But feels like there's not a ton left for the error to catch after that, the test currently just tests constants. https://github.com/PyCQA/flake8-bugbear/blob/main/tests/b030.py

[JelleZijlstra]

We should definitely allow splats, I'll send a PR. We discussed this a bit on #346 and landed on disallowing calls, but if there's real use cases where people use calls, we can revisit that decision.

[samueljsb]

To be clear, the function call happened once in our 35k-module codebase -- I've refactored it to assign the returned set of exceptions to a variable and it's now much clearer what's going on so please don't take this as a vote to allow function calls from me!