Description:
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The second argument of php_check_syntax is supposed to be passed by reference. However, you need to specify the reference where the function is called, like php_check_syntax($file, &$error); resulting in

Warning: Call-time pass-by-reference has been deprecated - argument passed by value;  If you would like to pass it by reference, modify the declaration of php_check_syntax().  If you would like to enable call-time pass-by-reference, you can set allow_call_time_pass_reference to true in your INI file.  However, future versions may not support this any longer.

Reproduce code:
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php_check_syntax("test.php", $error);

Expected result:
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errorstring in $error

Actual result:
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Notice: Undefined variable:  error