Comment 1 for bug 1515372

See also duplicate bug #1532584 where the same pathological behavior is reached by using an invalid component type while parsing the system.

The way defsystem is parsed should be revised.

Solution 1: have an unwind-protect unregister the system if the evaluation failed.

Solution 2: have a flag in the system that indicates whether it's been successfully parsed; if not, report error, or reparse, or ouch. [Sounds more complex, for less results]

Solution 3: rewrite the entire parsing infrastructure inherited from ASDF 1, with something better that works bottom up rather than top down (though it will have to maintain a top-down context; so I suppose that really means, distinguishing build-time component context objects from finished component objects; meh).