Detect variable reuse with different type

[szepeviktor]

Feature request

I think this is okay.

$var = 'apple';
$var = 'nice ' . $var;

But many developers tend to stuff other type into the same variable.

$list = [1, 2, 3];
$list = \implode(', ', $list);

Could PHPStan warn me when a variable's type changes?

[szepeviktor]

Even this.

$list = [1, 2, 3];
$list = 'apple';

[ondrejmirtes]

It's really easy to implement your custom rule that checks this, but it's hard to not be too annoying, for example in cases like these:

$test = null;
if (rand(0, 1)) {
    $test = new Foo();
}

[szepeviktor]

implement your custom rule

Okay :) so it is up to me?

Could you start me up with 2 sentences?

[szepeviktor]

/** @var Foo|null $test */
$test = null;
if (rand(0, 1)) {
    $test = new Foo();
}

[ondrejmirtes]

1. https://phpstan.org/developing-extensions/rules
2. getNodeType should return Assign::class
3. in processNode you should check that on the left side (var property of $node) there's Variable node. If not, return [].
4. Ask scope about $scope->hasVariableType. If it's not yes(), return []
5. Get current type of the variable from scope, and compare it with $scope->getType($node->expr). You can use Type::equals() or Type::isSuperTypeOf, depends on your requirements.
6. Return message if the types are different enough.

[szepeviktor]

Thank you.