CLJS-982: Var derefing should respect Clojure semantics

Var derefing now happens via a thunk. This supports the Clojure pattern
of passing a function to some library you don't control where you still
want redef to work correctly.

src/clj/cljs/compiler.clj

@@ -254,8 +254,10 @@
 
 (defmethod emit* :var-special
   [{:keys [env var sym meta] :as arg}]
-  (emit-wrap env
-    (emits "new cljs.core.Var(" var "," sym ","  meta ")")))
+  (let [{:keys [name]} (:info var)]
+    (emit-wrap env
+      (emits "new cljs.core.Var(function(){return " (munge name) ";},"
+        sym "," meta ")"))))
 
 (defmethod emit* :meta
   [{:keys [expr meta env]}]

src/cljs/cljs/core.cljs

@@ -631,55 +631,55 @@
 
 (deftype Var [val sym _meta]
   IDeref
-  (-deref [_] val)
+  (-deref [_] (val))
   IMeta
   (-meta [_] _meta)
   Fn
   IFn
   (-invoke [_]
-    (val))
+    ((val)))
   (-invoke [_ a]
-    (val a))
+    ((val) a))
   (-invoke [_ a b]
-    (val a b))
+    ((val) a b))
   (-invoke [_ a b c]
-    (val a b c))
+    ((val) a b c))
   (-invoke [_ a b c d]
-    (val a b c d))
+    ((val) a b c d))
   (-invoke [_ a b c d e]
-    (val a b c d e))
+    ((val) a b c d e))
   (-invoke [_ a b c d e f]
-    (val a b c d e f))
+    ((val) a b c d e f))
   (-invoke [_ a b c d e f g]
-    (val a b c d e f g))
+    ((val) a b c d e f g))
   (-invoke [_ a b c d e f g h]
-    (val a b c d e f g h))
+    ((val) a b c d e f g h))
   (-invoke [_ a b c d e f g h i]
-    (val a b c d e f g h i))
+    ((val) a b c d e f g h i))
   (-invoke [_ a b c d e f g h i j]
-    (val a b c d e f g h i j))
+    ((val) a b c d e f g h i j))
   (-invoke [_ a b c d e f g h i j k]
-    (val a b c d e f g h i j k))
+    ((val) a b c d e f g h i j k))
   (-invoke [_ a b c d e f g h i j k l]
-    (val a b c d e f g h i j k l))
+    ((val) a b c d e f g h i j k l))
   (-invoke [_ a b c d e f g h i j k l m]
-    (val a b c d e f g h i j k l m))
+    ((val) a b c d e f g h i j k l m))
   (-invoke [_ a b c d e f g h i j k l m n]
-    (val a b c d e f g h i j k l m n))
+    ((val) a b c d e f g h i j k l m n))
   (-invoke [_ a b c d e f g h i j k l m n o]
-    (val a b c d e f g h i j k l m n o))
+    ((val) a b c d e f g h i j k l m n o))
   (-invoke [_ a b c d e f g h i j k l m n o p]
-    (val a b c d e f g h i j k l m n o p))
+    ((val) a b c d e f g h i j k l m n o p))
   (-invoke [_ a b c d e f g h i j k l m n o p q]
-    (val a b c d e f g h i j k l m n o p q))
+    ((val) a b c d e f g h i j k l m n o p q))
   (-invoke [_ a b c d e f g h i j k l m n o p q r]
-    (val a b c d e f g h i j k l m n o p q r))
+    ((val) a b c d e f g h i j k l m n o p q r))
   (-invoke [_ a b c d e f g h i j k l m n o p q r s]
-    (val a b c d e f g h i j k l m n o p q r s))
+    ((val) a b c d e f g h i j k l m n o p q r s))
   (-invoke [_ a b c d e f g h i j k l m n o p q r s t]
-    (val a b c d e f g h i j k l m n o p q r s t))
+    ((val) a b c d e f g h i j k l m n o p q r s t))
   (-invoke [_ a b c d e f g h i j k l m n o p q r s t rest]
-    (apply val a b c d e f g h i j k l m n o p q r s t rest)))
+    (apply (val) a b c d e f g h i j k l m n o p q r s t rest)))
 
 ;;;;;;;;;;;;;;;;;;; fundamentals ;;;;;;;;;;;;;;;
 

test/cljs/cljs/core_test.cljs

@@ -2624,6 +2624,19 @@
     (is (= (get m 3) 4))
     (is (= m {1 2 3 4}))))
 
+(defn foo-var [f]
+  (fn [x]
+    (f x)))
+
+(defn foo-set [x]
+  (first x))
+
+(deftest test-cljs-982-var-deref []
+  (let [f (foo-var #'foo-set)]
+    (is (= (f [1 2 3]) 1))
+    (set! foo-set (fn [x] :oops))
+    (is (= (f [1 2 3]) :oops))))
+
 (comment
   ;; ObjMap
   ;; (let [ks (map (partial str "foo") (range 500))