Phan doesn't narrow property types after explicit tests

[jdwx]

Given the following example:

<?php

function DoubleInt( int $i ) : int {
	return $i * 2;
}

function DoubleIntOrNull( ?int $i ) : ?int {
	if ( is_int( $i ) )
		return DoubleInt( $i );
	return null;
}

class Example {

	/** @var ?int */
	protected $i;

	function __construct( ?int $i ) {
		$this->i = $i;
	}

	function doubleMe() : ?int {
		if ( is_int( $this->i ) )
			return DoubleInt( $this->i );
		return null;
	}

}

$ex = new Example( 5 );
echo $ex->doubleMe(), "\n";

Phan will produce a warning for the Example::doubleMe() method, but not for the DoubleIntOrNull() function:

$ phan types.php
types.php:24 PhanTypeMismatchArgument Argument 1 (i) is ?int but \DoubleInt() takes int defined at types.php:3

It looks like Phan doesn't allow the type union of $this->i to be updated within the scope of the if statement the way it does for local variables and parameters. (Or after it, when an else clause appears or simplify_ast is used.)

Workarounds in the code are to copy the property to a local variable, or to explicitly cast it at the point of use when its type has been checked.

Thanks!

[TysonAndre]

This issue is a consequence of pre-existing issues: #204 and #538

[jdwx]

Updating this with a shorter self-contained example that has come up today:

<?php

class Foo {
	/** @var ?string $bar */
	public $bar;
}

$foo = new Foo;
if ( is_string( $foo->bar ) )
	echo "strlen = ", strlen( $foo->bar ), "\n";

[TysonAndre]

Early (broken) work is included in TysonAndre#113 . This needs to be rebased, and tests are still failing.

Additionally, inferences in the global scope may require more work.