Allow handling of multiple calls of the same option.

src/main/clojure/clojure/tools/cli.clj

@@ -51,7 +51,7 @@
   [specs]
   (reduce (fn [m s]
             (if (contains? s :default)
-              (assoc m (:name s) (:default s))
+              ((:assoc-fn s) m (:name s) (:default s))
               m))
           {} specs))
 
@@ -72,12 +72,12 @@
          (throw (Exception. (str "'" opt "' is not a valid argument")))
 
          (and (opt? opt) (spec :flag))
-         (recur (assoc options (spec :name) (flag-for opt))
+         (recur ((spec :assoc-fn) options (spec :name) (flag-for opt))
                 extra-args
                 (rest args))
 
          (opt? opt)
-         (recur (assoc options (spec :name) ((spec :parse-fn) (second args)))
+         (recur ((spec :assoc-fn) options (spec :name) ((spec :parse-fn) (second args)))
                 extra-args
                 (drop 2 args))
 
@@ -105,6 +105,7 @@
             :aliases  (set aliases)
             :name     (keyword (last aliases))
             :parse-fn identity
+            :assoc-fn assoc
             :flag     flag}
            (when flag {:default false})
            options)))

src/test/clojure/clojure/tools/cli_test.clj

@@ -58,6 +58,17 @@
              (first (cli ["-s" "localhost"]
                          ["-s" "--server"]))))))
 
+  (testing "merging args"
+    (deftest should-merge-identical-arguments
+      (let [assoc-fn (fn [previous key val]
+                       (assoc previous key
+                         (if-let [oldval (get previous key)]
+                           (merge oldval val)
+                           (hash-set val))))
+            [options args _] (cli ["-p" "1" "--port" "2"]
+                                  ["-p" "--port" "description" :assoc-fn assoc-fn])]
+        (is (= {:port #{"1" "2"}} options)))))
+
   (testing "extra arguments"
     (deftest should-provide-access-to-trailing-args
       (let [[options args _] (cli ["--foo" "bar" "a" "b" "c"]