how we handled externs in compiler state was just not very functional

one problem is that we always *compute* extern information when
analyzing files, not having externs in compiler state just means that
extern information is wrong.

another problem is that :infer-externs may be discovered *after* the
compiler evironment is built, meaning we end up back at problem one.

just memoize it, make it easier to change our mind later, fix tests

src/main/clojure/cljs/analyzer.cljc

@@ -168,6 +168,9 @@
 (defn compiler-options []
   (get @env/*compiler* :options))
 
+(defn get-externs []
+  (::externs @env/*compiler*))
+
 (defn checked-arrays
   "Returns false-y, :warn, or :error based on configuration and the
    current value of *unchecked-arrays*."
@@ -1005,7 +1008,7 @@
 
 (defn has-extern?
   ([pre]
-    (has-extern? pre (get @env/*compiler* ::externs)))
+   (has-extern? pre (get-externs)))
   ([pre externs]
    (or (has-extern?* pre externs)
        (when (= 1 (count pre))
@@ -1018,7 +1021,7 @@
   ([pre]
    (js-tag pre :tag))
   ([pre tag-type]
-   (js-tag pre tag-type (get @env/*compiler* ::externs)))
+   (js-tag pre tag-type (get-externs)))
   ([pre tag-type externs]
    (js-tag pre tag-type externs externs))
   ([pre tag-type externs top]

src/main/clojure/cljs/compiler.cljc

@@ -201,7 +201,7 @@
                     (sorted-map))))))))))
   (emit* ast))
 
-(defn emits 
+(defn emits
   ([])
   ([^Object a]
    (cond
@@ -587,12 +587,12 @@
 (defn emit-js-array [items comma-sep]
   (emits "[" (comma-sep items) "]"))
 
-(defmethod emit* :js-object 
+(defmethod emit* :js-object
   [{:keys [keys vals env]}]
   (emit-wrap env
     (emit-js-object (map vector keys vals) identity)))
 
-(defmethod emit* :js-array 
+(defmethod emit* :js-array
   [{:keys [items env]}]
   (emit-wrap env
     (emit-js-array items comma-sep)))
@@ -1133,7 +1133,7 @@
         protocol (:protocol info)
         tag      (ana/infer-tag env (first (:args expr)))
         proto? (and protocol tag
-                 (or (and ana/*cljs-static-fns* protocol (= tag 'not-native)) 
+                 (or (and ana/*cljs-static-fns* protocol (= tag 'not-native))
                      (and
                        (or ana/*cljs-static-fns*
                            (:protocol-inline env))
@@ -1817,8 +1817,7 @@
 (defn emit-externs
   ([externs]
    (emit-externs [] externs (atom #{})
-     (when env/*compiler*
-       (::ana/externs @env/*compiler*))))
+     (when env/*compiler* (ana/get-externs))))
   ([prefix externs top-level known-externs]
    (loop [ks (seq (keys externs))]
      (when ks

src/main/clojure/cljs/env.cljc

@@ -45,13 +45,12 @@ state that is accessed/maintained by many different components."}
 
 (defn default-compiler-env* [options]
   (merge
-    {:cljs.analyzer/namespaces {'cljs.user {:name 'cljs.user}}
+    {:cljs.analyzer/namespaces     {'cljs.user {:name 'cljs.user}}
      :cljs.analyzer/constant-table {}
-     :cljs.analyzer/data-readers {}
-     :cljs.analyzer/externs #?(:clj  (when (:infer-externs options)
-                                       (externs/externs-map (:externs-sources options)))
-                               :cljs nil)
-     :options options}
+     :cljs.analyzer/data-readers   {}
+     :cljs.analyzer/externs        #?(:clj  (externs/externs-map (:externs-sources options))
+                                      :cljs nil)
+     :options                      options}
     #?@(:clj [(when (= (:target options) :nodejs)
                 {:node-module-index deps/native-node-modules})
               {:js-dependency-index (deps/js-dependency-index options)}])))

src/main/clojure/cljs/externs.clj

@@ -182,11 +182,11 @@
         (seq xs) (update-in xs merge {})))
     {} externs))
 
-(defn externs-map
+(defn externs-map*
   ([]
-   (externs-map (CommandLineRunner/getDefaultExterns)))
+   (externs-map* (CommandLineRunner/getDefaultExterns)))
   ([sources]
-   (externs-map sources
+   (externs-map* sources
      '{eval {}
        global {}
        goog {nodeGlobalRequire {}}
@@ -204,6 +204,8 @@
            externs (index-externs (parse-externs externs-file))))
        defaults sources))))
 
+(def externs-map (memoize externs-map*))
+
 (defn ns-match? [ns-segs var-segs]
   (or
     ;; exact match (i.e. ctors)

src/test/clojure/cljs/analyzer_tests.clj

@@ -179,9 +179,9 @@
             (.getMessage (.getCause e))))
         "Only one ")))
 
-(def test-cenv (atom {}))
+(def test-cenv (env/default-compiler-env))
 (def test-env (assoc-in (ana/empty-env) [:ns :name] 'cljs.core))
-(def test-core-env (atom {}))
+(def test-core-env (env/default-compiler-env))
 
 (binding [ana/*unchecked-if* false
           ana/*analyze-deps* false]