Strange behavior with :function output translations and custom output-files method

[Jason Miller]

Hi,

I reduced a  testcase from the metacopy-with-contextl .asd file.  It
defines an output-files method to rename the .fasl so that it can
compile the same lisp files with different features set.

This worked fine when I was using normal output translations, but when I
switched to a :function output translation, it failed.  I'm not sure if
this is a bug in asdf, a bug in my output translation function or a bug
in metacopy, so I'm posting it here for some advice.

Test-case is in a tarball below.  There is a shell script "test.sh"
which invokes sbcl twice.  The first time the output translation is left
unaltered, the second time it specifies a :function translator for all
paths, and this causes an error.

-Jason

https://phab.jasomfiles.org/orfiles/asdtest.tar.gz