A number of vars from clojure.repl, clojure.java.javadoc, and clojure.pprint are unconditionally referred into *ns* by clojure.main/repl. This is fine when it is being used e.g. as the primary driver of a terminal-bound Clojure REPL, but other usages can end up bringing those utility vars into namespaces other than 'user. This can cause problems if clojure.main/repl is used to drive a REPL within namespaces that already have referred or interned vars with the same names as those utility vars, e.g.:
$ java -jar ~/.m2/repository/org/clojure/clojure/1.5.0-alpha6/clojure-1.5.0-alpha6.jar
Clojure 1.5.0-alpha6
user=> (ns foo)
nil
foo=> (defn pp [] "hi!")
#'foo/pp
foo=> (pp)
"hi!"
foo=> (clojure.main/repl)
foo=> (pp)
nil
nil
foo=> (defn pp [] "whoops")
CompilerException java.lang.IllegalStateException: pp already refers to: #'clojure.pprint/pp in namespace: foo, compiling:(NO_SOURCE_PATH:7:1)
Worse, nREPL uses clojure.main/repl (in large part to maximize the consistency of REPL behaviour across different Clojure versions), where each user expression is evaluated through a separate clojure.main/repl invocation. This leads to the same problems as above, but for every nREPL user, session, and expression (reported @ NREPL-31).
A simple fix for this is to perform these refers only if *ns* is 'user (which, AFAICT, was the only intended effect of CLJ-310, CLJ-454, and https://github.com/clojure/clojure/commit/04764db, the changes that added these automatic implicit refers to clojure.main/repl).
Defect
Closed
Major
Patch attached to only refer in the utility vars if in the user namespace.