there's a problem with WITH-FOREIGN-SLOTS that shows up when a c-struct is defined in one package and used from another one. here's an example:

(in-package :cl-user)

(defpackage :internals (:use :cl :cffi))

(defpackage :mypackage (:use :cl :cffi))

(in-package :internals)

(defcstruct foo (x :int))

(in-package :mypackage)

(with-foreign-object (fooptr 'internals::foo) (with-foreign-slots ((x) fooptr internals::foo) x))

(with-foreign-slots ((x) fooptr internals::foo) x) gets expanded to

(LET ((#:PTR2455 FOOPTR)) (SYMBOL-MACROLET ((X (FOREIGN-SLOT-VALUE #:PTR2455 'INTERNALS::FOO 'X))) X))

instead of

(LET ((#:PTR2455 FOOPTR)) (SYMBOL-MACROLET ((X (FOREIGN-SLOT-VALUE #:PTR2455 'INTERNALS::FOO 'INTERNALS::X))) X)) ; ^^^^^^^^^^^

the attached patch fixes this