runtime existence check for :require-global libs under :optimizations :none (#270)

Author: swannodette

src/main/clojure/cljs/compiler.cljc

@@ -1312,19 +1312,24 @@
       (apply str
         (map #(str "['" % "']") xs)))))
 
-(defn emit-global-export [ns-name global-exports lib]
-  (let [[lib' sublib] (ana/lib&sublib lib)]
+(defn emit-global-export [ns-name global-exports lib opts]
+  (let [[lib' sublib] (ana/lib&sublib lib)
+        ref (str "goog.global"
+              ;; Convert object dot access to bracket access
+              (->> (string/split (name (or (get global-exports (symbol lib'))
+                                           (get global-exports (name lib'))))
+                     #"\.")
+                (map (fn [prop] (str "[\"" prop "\"]")))
+                (apply str)))]
+    (when (and (ana/external-dep? lib')
+               (= :none (:optimizations opts)))
+      (emitln
+        "if(!" ref ") throw new Error(\"External library, " lib' ", never provided\");"))
     (emitln
       (munge ns-name) "."
       (ana/munge-global-export lib)
-      " = goog.global"
-      ;; Convert object dot access to bracket access
-      (->> (string/split (name (or (get global-exports (symbol lib'))
-                                   (get global-exports (name lib'))))
-             #"\.")
-        (map (fn [prop]
-               (str "[\"" prop "\"]")))
-        (apply str))
+      " = "
+      ref
       (sublib-select sublib)
       ";")))
 
@@ -1409,7 +1414,7 @@
     ;; Global Exports
     (doseq [lib global-exports-libs]
       (let [{:keys [global-exports]} (get js-dependency-index (name (-> lib ana/lib&sublib first)))]
-        (emit-global-export ns-name global-exports lib)))
+        (emit-global-export ns-name global-exports lib options)))
     (when (-> libs meta :reload-all)
       (emitln "if(!COMPILED) " loaded-libs " = cljs.core.into(" loaded-libs-temp ", " loaded-libs ");"))))