Crash of interpreter due to assign before global declaration

[Eclips4]

Crash report

What happened?

def bar():
    x = 11
    global x
    return x

bar()

Traceback:

File "/Users/admin/Projects/cpython/example.py", line 3
    global x
    ^^^^^^^^
SyntaxError: name 'x' is assigned to before global declaration
Assertion failed: ((gc->_gc_next & NEXT_MASK_UNREACHABLE) == next_value), function validate_list, file gcmodule.c, line 403.
zsh: abort      ./python.exe example.py

CPython versions tested on:

CPython main branch

Operating systems tested on:

macOS

Output from running 'python -VV' on the command line:

No response

Linked PRs

• gh-111132: Fix crash on interactive_filename in run_mod #111136

[Eclips4]

Bisected to e1d8c65
cc @pablogsal

[chgnrdv]

FYI, these are examples of code that hit the same assertion:

def f(x):
    global x

def f():
    global x
    nonlocal x

def f():
    nonlocal x

nonlocal x

[chgnrdv]

Commenting out this decref made issue go away.

cpython/Python/pythonrun.c

Lines 1279 to 1281 in 37e4e20

	if (co == NULL) {
	Py_DECREF(interactive_filename);
	return NULL;

[pablogsal]

Thanks a lot @sobolevn for the fix and @Eclips4 for the report!