CLJS-806: support ^:const

def now supports const making the var a constant (i.e. no redefining or setting).
The emitted definition has the @const JSDoc tag added to it. Support for constants
has been added to the case macro.

Author: spinningtopsofdoom

src/clj/cljs/analyzer.clj

@@ -684,10 +684,13 @@
         tests    (mapv #(mapv (fn [t] (analyze expr-env t)) %) tests)
         thens    (mapv #(analyze env %) thens)
         default  (analyze env default)]
-    (assert (every? (fn [t] (and (= :constant (:op t))
-                              ((some-fn number? string? char?) (:form t))))
+    (assert (every? (fn [t]
+                      (or
+                        (-> t :info :const)
+                        (and (= :constant (:op t))
+                             ((some-fn number? string? char?) (:form t)))))
               (apply concat tests))
-      "case* tests must be numbers or strings")
+      "case* tests must be numbers, strings, or constants")
     {:env env :op :case* :form form
      :v v :tests tests :thens thens :default default
      :children (vec (concat [v] tests thens (if default [default])))}))
@@ -783,6 +786,8 @@
          :var (symbol (str ns-name) (str sym))}))
     (when (namespace sym)
       (throw (error env "Can't def ns-qualified name")))
+    (when (:const (resolve-var (dissoc env :locals) sym))
+      (throw (error env "Can't redefine a constant")))
     (when-let [doc (:doc args)]
       (when-not (string? doc)
         (throw (error env "Too many arguments to def"))))
@@ -1178,6 +1183,8 @@
 
                        (symbol? target)
                        (do
+                         (when (:const (resolve-var (dissoc env :locals) target))
+                           (throw (error env "Can't set! a constant")))
                          (let [local (-> env :locals target)]
                            (when-not (or (nil? local)
                                          (and (:field local)

src/clj/cljs/core.clj

@@ -1481,9 +1481,10 @@
                            (assoc-test m test expr env)))
                      {} (partition 2 clauses))
              esym    (gensym)
+             const? #(:const (and (list? %) (ana/resolve-var env (last %))))
              tests   (keys pairs)]
     (cond
-      (every? (some-fn core/number? core/string? core/char?) tests)
+      (every? (some-fn core/number? core/string? core/char? const?) tests)
       (core/let [no-default (if (odd? (count clauses)) (butlast clauses) clauses)
                  tests      (mapv #(if (seq? %) (vec %) [%]) (take-nth 2 no-default))
                  thens      (vec (take-nth 2 (drop 1 no-default)))]

test/clj/cljs/analyzer_tests.clj

@@ -328,4 +328,19 @@
 (deftest test-cljs-1105
   ;; munge turns - into _, must preserve the dash first
   (is (not= (a/gen-constant-id :test-kw)
-            (a/gen-constant-id :test_kw))))
+            (a/gen-constant-id :test_kw))))
+;; Constants
+
+(deftest test-constants
+ (is (.startsWith
+        (try
+          (a/analyze test-env '(do (def ^:const foo 123)  (def foo 246)))
+          (catch Exception e
+            (.getMessage e)))
+        "Can't redefine a constant"))
+  (is (.startsWith
+        (try
+          (a/analyze test-env '(do (def ^:const foo 123)  (set! foo 246)))
+          (catch Exception e
+            (.getMessage e)))
+        "Can't set! a constant")))