Description:
------------
This case breaks autoloading, because of an apparent assumption in the way spl_autoload processes its registered functions:

namespace BaseLibrary
{
    class Loader
    {
         protected static $ns=__NAMESPACE__;
         protected static $dir=__DIR__;

         function Load($class_name)
         {
             // ...fully tested code for autoloading classes
             // using static::$ns and static:$dir...
         }
    }

    class SomeClass
    {
    }
}

namespace DerivedLibrary
{
    class Loader extends \BaseLibrary\Loader
    {
        protected static $ns=__NAMESPACE__;
        protected static $dir=__DIR__;
    }

    class SomeClass extends \BaseLibrary\SomeClass
    {
    }
}

When an attempt is made to load \DerivedLibrary\SomeClass, spl_autoload finds it correctly, include()s the file, but then never calls \BaseLibrary\Loader::Load('\BaseLibrary\SomeClass') -- which is necessary because \DerivedLibrary\SomeClass extends \BaseLibrary\SomeClass and \DerivedLibrary\Loader extends \BaseLibrary\Loader.

It simply throws "Class does not exist."

My guess is that the spl_autoload queue uses globally scoped data rather than function-scoped (stack) data to manage its traversal of the autoload functions, OR because spl_autoload peeks at the function call stack to ascertain which autoloaders it has already called (probably to avoid loops).

If \DerivedLibrary\Loader is made into a verbatim copy of \BaseLibrary\Loader (i.e., copying the file and changing only the namespace declaration -- thereby implicitly removing the 'extends \BaseLibrary\Loader') ... then immediately everything works!