Bug report

On PHPStan 0.12.33 under Windows 10, PHP 7.4.6.

PHPStan hangs on processing this file (chopped down from working code, this code does not make sense):

Code snippet that reproduces the problem

function fred($request)
	{
		$keys = '';
		foreach ($request as $index)
			{
			foreach ($index as $field)
				{
				if (isset($keys[$field]))
					{
					$keys[$field] = 0;
					}
				}
			}
	}

Expected output

PHPStan finishes, probably with some errors, but it never returns.

It is the first and only file processed. Level 1. If you change just about anything, it does not hang. This is the smallest snippet of code I could make hang. It was hanging on old production code, so pretty sure the code is valid PHP and works correctly with no errors or warnings reported.