LRUCache.__copy__ is still unsound

[cmanallen]

How do you use Sentry?

Sentry Saas (sentry.io)

Version

latest git revision

Steps to Reproduce

Mutable references are copied -- not the underlying value. This is visible here:

sentry-python/sentry_sdk/_lru_cache.py

Line 26 in f6281f5

new._data = self._data.copy()

Where we copy the _data attribute and not deepcopy.

class MutableObject:
    def __init__(self):
        self.count = 0

cache1 = LRUCache(max_size=2)
cache1.set(1, MutableObject())

cache2 = cache1.__copy__()
node = cache2.get(1)
node.count += 1

assert cache1.get(1).count == 0  # fail
assert cache2.get(1).count == 1

We should not be manually implementing __copy__ at all. This is a general helper class and should not assume copy semantics. I lay out this case in this comment and this comment.

Expected Result

Mutable objects do not pollute copied caches.

Actual Result

Mutable objects do pollute copied caches.