If array keys are known, they should be used to infer lookup types

[MaartenStaa]

Feature request

If I have two arrays, each of which have a defined shape, PHPStan should be able to figure out the value of array lookups. For example:

<?php declare(strict_types = 1);

/**
 * @return array{
 *	a: int[],
 * 	b: int[],
 *	c: bool
 * }
 */
function foo(): array {
	return [
		'a' => [1, 2],
		'b' => [3, 4, 5],
		'c' => true,
	];
}

$x = foo();
$test = ['a' => true, 'b' => false];
foreach ($test as $key => $value) {
	if ($value) {
		foreach ($x[$key] as $id) {
			echo $id, PHP_EOL;
		}
	}
}

This results in an error on the foreach line: "Argument of an invalid type array|bool supplied for foreach, only iterables are supported." (playground link). However, PHPStan should "know" that $key has type 'a'|'b', both of which would be keys on $x that contain values that are valid to iterate over.

[staabm]

A workaround is to introduce a temp var before the inner foreach, it works like expected
https://phpstan.org/r/8c20db8c-1f23-4af1-bbff-35c5ec6b9cb7

[ondrejmirtes]

This was recently fixed and works in PHPStan 1.4.4.

[github-actions]

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