CLJS-667: validate extend-type and extend-protocol shape

Author: swannodette

src/clj/cljs/analyzer.clj

@@ -70,7 +70,8 @@
    :protocol-multiple-impls true
    :single-segment-namespace true
    :munged-namespace true
-   :ns-var-clash true})
+   :ns-var-clash true
+   :extend-type-invalid-method-shape true})
 
 (def js-reserved
   #{"abstract" "boolean" "break" "byte" "case"
@@ -214,6 +215,11 @@
   [warning-type {:keys [ns var] :as info}]
   (str "Namespace " ns " clashes with var " var))
 
+(defmethod error-message :extend-type-invalid-method-shape
+  [warning-type {:keys [protocol method] :as info}]
+  (str "Bad extend-type method shape for protocol " protocol " method " method
+       ", method arities must be grouped together"))
+
 (defn ^:private default-warning-handler [warning-type env extra]
   (when (warning-type *cljs-warnings*)
     (when-let [s (error-message warning-type extra)]

src/clj/cljs/core.clj

@@ -875,8 +875,14 @@
             impls   (drop-while seq? (next impls))]
         (when (contains? protos proto)
           (ana/warning :protocol-multiple-impls env {:protocol proto}))
-        (core/doseq [method methods]
-          (validate-impl-sigs env proto method))
+        (loop [seen #{} methods methods]
+          (when (seq methods)
+            (let [[fname :as method] (first methods)]
+              (when (contains? seen fname)
+                (ana/warning :extend-type-invalid-method-shape env
+                  {:protocol proto :method fname}))
+              (validate-impl-sigs env proto method)
+              (recur (conj seen fname) (next methods)))))
         (recur (conj protos proto) impls)))))
 
 (defmacro extend-type