slurp erroneously prints a warning unless encoding is explicitly provided:
$ touch foo
$ clojure -M -e '(slurp "foo")'
$ Clojure.Main -e '(slurp "foo")'
WARNING: (slurp f enc) is deprecated, use (slurp f :encoding enc).
The cause of this is found in the
normalize-slurp-opts function, which differs from the JVM version here.