[moving this to slime-devel]
I recently banged my head against something similar. Turns out, mcclim loads swank, so be sure to delete .slime/fasl too.
been there... that's why my slime locally uses asdf:apply-output-translations for a few years now.
slime used to be proudly ASDF free, but maybe that's something to reconsider, at least with an optional support.
this is what i'm running with (which i don't recommend for inclusion in this form):
(defun binary-pathname (src-pathname binary-dir) "Return the pathname where SRC-PATHNAME's binary should be compiled." + (declare (ignore binary-dir)) + #+asdf + (asdf:apply-output-translations src-pathname) + #-asdf (let ((cfp (compile-file-pathname src-pathname))) (merge-pathnames (make-pathname :name (pathname-name cfp) :type (pathname-type cfp)))))
but if the maintainers are open for this direction, then i may look into packaging up and testing a PR for integrating ASDF properly, and optionally.
and not forgetting this either: https://github.com/slime/slime/pull/282/
currently swank can break in funny ways when used together with ASDF. e.g. :depends-on (:swank) can be a source of great bafflement when it reloads swank and undo's half of the contrib's, leaving some stuff crippled. and the .slime/fasl dir can also bite you when you thought you have deleted the fasl's, except one outlier.