Hi
I found a case where my expectations does not meet the results reported by ruff. But first, let's start with the issue basics:

• Keywords searched: "B006", "mutable default"
• Ruff version: ruff 0.4.0
• Command invoked: ruff check case.py --select ALL --ignore D,FA --isolated

Where my case.py contains the following lines:

DEFAULT_ENTRIES = [1, 2, 3]

def append_one(entries: list[int] = DEFAULT_ENTRIES) -> None:
    entries.append(1)

I would have hoped that this would be detected by rule B006 (or any other rule), but sadly it is not.

However, the rule detects the issue if instead of DEFAULT_ENTRIES we use [].
Thanks for checking!