PHPStan assumes that an array passed by reference to a callable cannot be changed inside the callable

[steffenweber]

Bug report

$ phpstan --version
PHPStan - PHP Static Analysis Tool 0.12.94

PHPStan seems to assume that an array passed by reference to a callable cannot be changed inside the callable. In the following code snippet, PHPStan claims that the array is empty ("Empty array passed to foreach" on line 14) although it could have been changed by the callable.

Code snippet that reproduces the problem

<?php declare(strict_types = 1);

class HelloWorld
{
	/**
	 * @param string $key
	 * @param callable(array<string> &$tags): string $callback
	 */
	public function get($key, callable $callback): string
	{
		$tags = [];
		$value = $callback($tags);

		foreach ($tags as $tag)
		{
			echo "$tag\n";
		}

		return $value;
	}
}

 ------ -------------------------------- 
  Line   phpstan-testcase.php                    
 ------ -------------------------------- 
  14     Empty array passed to foreach.  
 ------ --------------------------------

https://phpstan.org/r/8912aef0-2aba-4301-b268-647406e82999

Expected output

No errors.

Did PHPStan help you today? Did it make you happy in any way?

PHPStan helped me find unreachable code last Friday. :)

[steffenweber]

So I guess this issue is similar to issue #5429 but I'm not sure how to tell PHPStan that the callback function is impure. 🤔

[ondrejmirtes]

In theory PHPStan should be able to pick up the &$tags part and invalidate the variable based on that.

[phpstan-bot]

@steffenweber After the latest commit in dev-master, PHPStan now reports different result with your code snippet:

@@ @@
-14: Empty array passed to foreach.
+No errors

[ondrejmirtes]

Fixed: phpstan/phpstan-src@109bf99

[github-actions]

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