If I add an explicit dependency on setup in the :simple ASDF system above like this:
:depends-on (:net.didierverna.clon.setup :net.didierverna.clon))
the problem goes away. This doesn't happen with the 5 other Lisp implementations that I've tested.
Also, it may be worth mentioning that Clon's setup system gets a special treatment. It's loaded explicitly at the top of several .asd files like this (with the utmost disrespect for the Almighty ASDF Gods recommendations):
(asdf:load-system :net.didierverna.clon.setup)
I'm wondering if this may have something to do with the problem.
Your system definition was wrong, and you found the way to fix it.
Your manual (asdf:load-system ...) from the .asd file is equivalent to a :defsystem-depends-on dependency. It creates a dependency at system-definition-time, but not at runtime. Not at runtime, ergo, not to be included in the executable.
If it defines packages that are required in the executable, it MUST be added as a load-time dependency as well as a system-definition-time dependency. It is a BUG in YOUR code that clon fails to depend on clon.setup.
—♯ƒ • François-René ÐVB Rideau •Reflection&Cybernethics• http://fare.tunes.org Director is a misnomer. You're a hoper. You put all these people together and you hope it all works out. — Frank Oz, director of "Dirty Rotten Scoundrels"