False positive `used-before-assignment` when usage and assignment guarded by the same test in different statements

[tvandeveenzepp]

Bug description

The used-before-assignment check reports false positive for using the same variable inside multiple if __name__ == '__main__' statements.

# pylint: disable=missing-docstring

if __name__ == '__main__':
    X = 1

if __name__ == '__main__':
    print(X)

Configuration

No response

Command used

pylint test.py

Pylint output

************* Module test
test.py:7:10: E0601: Using variable 'X' before assignment (used-before-assignment)

-----------------------------------
Your code has been rated at 0.00/10

Expected behavior

No error.

Pylint version

pylint 2.16.0
astroid 2.14.1
Python 3.7.4 (tags/v3.7.4:e09359112e, Jul  8 2019, 20:34:20) [MSC v.1916 64 bit (AMD64)]

OS / Environment

No response

Additional dependencies

No response

[clavedeluna]

It would appear if __name__ == '__main__': is causing different behavior because if you do:

# pylint: disable=missing-docstring

if True:
    X = 1

if True:
    print(X)

the msg is not emitted. My hunch is this is happening because pylint isn't loading it as a script which is what if __name__ == '__main__': requires.

[jacobtylerwalls]

Likely met the "always false" test in #6677.

[jacobtylerwalls]

We may need to check if the variable is guarded again by the same(ish) test.

[saranti]

This bug wasn't present in v2.15.10. I'll take this up if no one objects

[jacobtylerwalls]

This also affects if TYPE_CHECKING: e.g.:

if TYPE_CHECKING:
    import math

if TYPE_CHECKING:
    assert math

This is because TYPE_CHECKING, like __name__ == '__main__', is false at runtime except under special circumstances, see #6677.