gh-128965: pickle load_build function checks if state is None, not False

[Legoclones]

Inside of the load_build() function for pickle's BUILD opcode, the C accelerator at one point checks if state is Py_None, while the Python version only checks if state.

cpython/Modules/_pickle.c

Line 6638 in 34ded1a

if (state != Py_None) {

cpython/Lib/pickle.py

Line 1765 in 34ded1a

if state:

This means if state is something like an empty dictionary or tuple, the code block under the if statement WILL be run in _pickle.c, but NOT in pickle.py.

As an example, the bytestream b']]b.' has the following disassembly:

    0: ]    EMPTY_LIST
    1: ]    EMPTY_LIST
    2: b    BUILD
    3: .    STOP
highest protocol among opcodes = 1

This will do nothing in pickle.py but error out in _pickle.c with the message state is not a dictionary. The easy solution is to change if state to if state != None, and it shouldn't break any existing functionality. I've attached a pull request.

• Issue: pickle load_build function checks if state is None, not False #128965

[picnixz]

Can we have tests that check this code path? Namely check that non-dict objects raise a TypeError and that falsey dicts do not raise exceptions? In addition, we need a NEWS entry for the bugfix, e.g:

Fix :meth:`!pickle._Pickler.load_build` for non-dictionary states.

(My NEWS entry is definitely poorly worded but I don't have a better suggestion for now. Maybe you can come up with a better formulation).

[picnixz]

Suggested change

	if state != None:
	if state is not None: