`used-before-assignment` false negative after conditionals

[eddieViscosity]

Running pylint on this simple example does not detect that x can be used before assignment. This is a very common programming mistake and should be caught.

def a_function(d):
    if d:
        x=1
    return x

Current behavior - Fails to detect x is used before assignment

Expected behavior: detect variable use inside logic branches.

pylint --version output: pylint-2 1.7.4

[kylebebak]

Just here to second this.

[nickdrozd]

Ran into this at work today!

[DanielNoord]

Do we want to create a new checker called possibly-used-before-assignment checker for this? Similar to how there is possibly-unused-variable. If we can't infer d we will never be able to emit used-before-assignment without any doubt.

[Pierre-Sassoulas]

possibly-unused-before-assignment

Did you mean "possibly-used-before-assignment" ?

[DanielNoord]

Yeah 😅

[Pierre-Sassoulas]

I think it makes sense. Adding a good control flow to astroid would be nice but is also difficult.

[nickdrozd]

This kind of problem would be avoided entirely if the variable were set with a ternary expression!

[jacobtylerwalls]

Duplicate of #267 but some good discussion here, so maybe we can choose one issue to keep open.

We can possibly explore handling this after the precedent in #5402 of storing consumed_uncertain (name to be finalized before merge).

[Pierre-Sassoulas]

There's some more example in #267 or #1807 for functional tests.