Keywords: extend-immutable-calls, B008, script, module, __main__
Ruff version: 0.3.7

Working MWE

In a directory containing just the file test.py:

from other_module import A

def f(a=A()):
    pass

checking with:

ruff check --isolated --select=B008 \
    --config 'lint.flake8-bugbear.extend-immutable-calls=["other_module.A"]' \
    test.py

yields no errors.

Buggy MWE

If I declare A in the script instead of importing it:

class A: pass

def f(a=A()):
    pass

now ruff will find a B008 error in the def line, no matter what I configure in extend-immutable-calls. I tried A, test.A, __main__.A, and even builtins.A and __builtins__.A. Nothing makes it recognize A() as an immutable call.