CLJS-1918: case needs a type hint for keywords case when using *warn-on-infer*

add keyword hint

Author: dnolen

src/main/clojure/cljs/core.cljc

@@ -2294,7 +2294,7 @@
                  tests (mapv #(if (seq? %) (mapv kw-str %) [(kw-str %)]) (take-nth 2 no-default))
                  thens (vec (take-nth 2 (drop 1 no-default)))]
         `(let [~esym ~e
-               ~esym (if (keyword? ~esym) (.-fqn ~esym) nil)]
+               ~esym (if (keyword? ~esym) (.-fqn ~(vary-meta esym assoc :tag 'cljs.core/Keyword)) nil)]
            (case* ~esym ~tests ~thens ~default)))
 
       ;; equality

src/test/clojure/cljs/analyzer_tests.clj

@@ -1009,3 +1009,16 @@
                :warnings ws
                :with-core? true})]
     (is (zero? (count @ws)))))
+
+(deftest test-cljs-1918-infer-with-case-keywords
+  (let [ws  (atom [])
+        res (infer-test-helper
+              {:forms '[(ns cjls-1918.core)
+                        (defn foo [x]
+                          (cljs.core/case x
+                            :foo 1
+                            nil))]
+               :externs ["src/test/externs/test.js"]
+               :warnings ws
+               :with-core? true})]
+    (is (zero? (count @ws)))))