CLJS-1516: better error message when calling macros with arity

When expanding a macro with an incorrect number
of arguments, emit invalid arity diagnostic reporting
the number of arguments decremented by 2 in order
to hide the count associated with special variables
&env and &form.

- The approach taken for regular JVM ClojureScript
   is to catch the ArityException and throw a new
   one with the count decremented by two.

- The approach taken for bootstrapped ClojureScript
   ---since a generic js/Error is thrown---is to instead
   add a check for multi-arity-fns to consult the meta
   in the invalid arity path to see if the function is
   actually a bootstrap macroexpander and to
   decrement by two in that case.

Author: mfikes

src/main/clojure/cljs/analyzer.cljc

@@ -34,7 +34,7 @@
                      [cljs.reader :as edn]))
   #?(:clj (:import [java.io File Reader PushbackReader]
                    [java.net URL]
-                   [clojure.lang Namespace Var LazySeq]
+                   [clojure.lang Namespace Var LazySeq ArityException]
                    [cljs.tagged_literals JSValue])))
 
 #?(:clj (set! *warn-on-reflection* true))
@@ -2349,7 +2349,10 @@
         (if-not (nil? mac-var)
           (#?@(:clj [binding [*ns* (create-ns *cljs-ns*)]]
                :cljs [do])
-            (let [form' (apply @mac-var form env (rest form))]
+            (let [form' (try
+                          (apply @mac-var form env (rest form))
+                          #?(:clj (catch ArityException e
+                                    (throw (ArityException. (- (.actual e) 2) (.name e))))))]
               (if #?(:clj (seq? form') :cljs (cljs-seq? form'))
                 (let [sym' (first form')
                       sym  (first form)]

src/main/clojure/cljs/core.cljc

@@ -2784,9 +2784,11 @@
                         (~'cljs$core$IFn$_invoke$arity$variadic
                           ~@(dest-args maxfa)
                           argseq#)))
-                   `(throw (js/Error.
-                             (str "Invalid arity: "
-                               (alength ~args-sym)))))))))
+                   (if (:macro meta)
+                     `(throw (js/Error.
+                               (str "Invalid arity: " (- (alength ~args-sym) 2))))
+                     `(throw (js/Error.
+                               (str "Invalid arity: " (alength ~args-sym))))))))))
          ~@(map fn-method fdecl)
          ;; optimization properties
          (set! (. ~name ~'-cljs$lang$maxFixedArity) ~maxfa)))))