CLJS-3373: Externs Inference issue with vars invoked from foreign libs (#173)

Fix invoke inference to handle invokes on vars from foreign libs. If
we have a :js-var we cannot know whether it is a function or property.
Note this is different from the `:js-fn-var` case where a provided
extern did disambiguate.

In the case of `:js-var` we throw away the leading prefix since the
types simply cannot be known.

Add a test case based on the one provided by Timothy Pratley.

Author: swannodette

src/main/clojure/cljs/analyzer.cljc

@@ -1514,15 +1514,31 @@
                              else-tag #{else-tag})]
               (into then-tag else-tag))))))))
 
-(defn infer-invoke [env {f :fn :keys [args] :as e}]
-  (let [me (assoc (find-matching-method f args) :op :fn-method)]
+(defn js-var? [ast]
+  (= :js-var (:op ast)))
+
+(defn js-var-fn? [fn-ast]
+  (js-var? (:info fn-ast)))
+
+(defn fn-ast->tag
+  [{:keys [info] :as fn-ast}]
+  (cond
+    ;; ClojureScript Fn
+    (:fn-var info)      (:ret-tag info)
+    ;; Global foreign JS Fn inferred via externs
+    (:js-fn-var info)   (:ret-tag info)
+    ;; Node foreign JS *var*, we cannot distinguish between properties
+    ;; and functions from such libs at this time, we cannot possibly
+    ;; know the returns so break the leading prefix (start with raw 'js tag)
+    (js-var-fn? fn-ast) 'js
+    :else               (when (= 'js (:ns info)) 'js)))
+
+(defn infer-invoke [env {fn-ast :fn :keys [args] :as e}]
+  (let [me (assoc (find-matching-method fn-ast args) :op :fn-method)]
     (if-some [ret-tag (infer-tag env me)]
       ret-tag
-      (let [{:keys [info]} f]
-        (if-some [ret-tag (if (or (true? (:fn-var info))
-                                  (true? (:js-fn-var info)))
-                            (:ret-tag info)
-                            (when (= 'js (:ns info)) 'js))]
+      (let []
+        (if-some [ret-tag (fn-ast->tag fn-ast)]
           ret-tag
           impl/ANY_SYM)))))
 

src/test/clojure/cljs/externs_infer_tests.clj

@@ -413,6 +413,26 @@
                  :with-core? true}))]
     (is (empty? @ws))))
 
+(deftest test-cljs-3373
+  (testing "var from foreign libraries that are invoked as fn should propagate 'js hints"
+    (let [ws  (atom [])
+          res (infer-test-helper
+                {:js-dependency-index {"firebase" {:global-exports '{firebase Firebase}}}
+                 :forms '[(ns foo.core
+                            (:require [firebase :refer [getAuth]]))
+                          (def auth
+                            (doto (getAuth)
+                              (.useDeviceLanguage)
+                              (.onAuthStateChanged (fn [user]))))]
+                 :warnings ws
+                 :warn true
+                 :with-core? false})]
+      (is (= (unsplit-lines
+               ["Object.getAuth;"
+                "Object.useDeviceLanguage;"
+                "Object.onAuthStateChanged;"])
+              res)))))
+
 (comment
   (binding [ana/*cljs-ns* ana/*cljs-ns*]
     (ana/no-warn