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I have noticed what I guess is a mistake in clojure.java.io namespace. The do-copy method here https://github.com/clojure/clojure/blob/master/src/clj/clojure/java/io.clj#L388 shoud have a ^File type metadata instead of ^Writer.
I think you're right, logged: https://clojure.atlassian.net/browse/CLJ-2724