Don't throw when subscribing to a non-existent sub

Fixes bug where we were logging if a sub didn't exist, but then trying
to create it still.

CHANGES.md

@@ -10,9 +10,13 @@
 - [#200](https://github.com/Day8/re-frame/pull/200) Remove trailing spaces from console logging 
 - [#248](https://github.com/Day8/re-frame/pull/200) Provide after interceptor with `db` coeffect, if no `db` effect was produced.
 - Add re-frame.loggers/get-loggers function to well, you know.
-- [#259](https://github.com/Day8/re-frame/pull/259) Fix a bug where registering a subscription would create and close over dependent subscriptions, meaning that they would never be garbage collected, and doing more work than necessary.
 - Added `clear-subscription-cache!` function. This should be used when hot reloading code to ensure that any bad subscriptions that cause rendering exceptions are removed. See [reagent-project/reagent#272](https://github.com/reagent-project/reagent/issues/272) for more details on this.
 
+#### Fixes
+
+- [#259](https://github.com/Day8/re-frame/pull/259) Fix a bug where registering a subscription would create and close over dependent subscriptions, meaning that they would never be garbage collected, and doing more work than necessary.
+- Fix a bug where subscribing to a subscription that didn't exist would throw an exception, instead of returning nil.
+
 ## 0.8.0  (2016.08.19)
 
 Staying on the leading edge of new buzzwords is obviously critical for any framework. 

src/re_frame/subs.cljc

@@ -70,9 +70,9 @@
      (let [query-id   (first-in-vector query-v)
            handler-fn (get-handler kind query-id)]
        ;(console :log "Subscription created: " query-v)
-       (if-not handler-fn
-         (console :error (str "re-frame: no subscription handler registered for: \"" query-id "\". Returning a nil subscription.")))
-       (cache-and-return query-v [] (handler-fn app-db query-v)))))
+       (if (nil? handler-fn)
+         (console :error (str "re-frame: no subscription handler registered for: \"" query-id "\". Returning a nil subscription."))
+         (cache-and-return query-v [] (handler-fn app-db query-v))))))
 
   ([v dynv]
    (if-let [cached (cache-lookup v dynv)]

test/re-frame/subs_test.cljs

@@ -1,15 +1,15 @@
 (ns re-frame.subs-test
-  (:require [cljs.test         :refer-macros [is deftest]]
+  (:require [cljs.test         :as test :refer-macros [is deftest]]
             [reagent.ratom     :refer-macros [reaction]]
             [re-frame.subs     :as subs]
             [re-frame.db       :as db]
             [re-frame.core     :as re-frame]))
 
+(test/use-fixtures :each {:before (fn [] (subs/clear-all-handlers!))})
+
 ;=====test basic subscriptions  ======
 
 (deftest test-reg-sub
-  (subs/clear-all-handlers!)
-
   (re-frame/reg-sub-raw
     :test-sub
     (fn [db [_]] (reaction (deref db))))
@@ -20,8 +20,6 @@
     (is (= 1 @test-sub))))
 
 (deftest test-chained-subs
-  (subs/clear-all-handlers!)
-
   (re-frame/reg-sub-raw
     :a-sub
     (fn [db [_]] (reaction (:a @db))))
@@ -44,8 +42,6 @@
     (is (= {:a 1 :b 3} @test-sub))))
 
 (deftest test-sub-parameters
-  (subs/clear-all-handlers!)
-
   (re-frame/reg-sub-raw
     :test-sub
     (fn [db [_ b]] (reaction [(:a @db) b])))
@@ -56,8 +52,6 @@
 
 
 (deftest test-sub-chained-parameters
-  (subs/clear-all-handlers!)
-
   (re-frame/reg-sub-raw
     :a-sub
     (fn [db [_ a]] (reaction [(:a @db) a])))
@@ -77,12 +71,13 @@
     (reset! db/app-db {:a 1 :b 2})
     (is (= {:a [1 :c], :b [2 :c]} @test-sub))))
 
+(deftest test-nonexistent-sub
+  (is (nil? (re-frame/subscribe [:non-existence]))))
 
 ;============== test cached-subs ================
 (def side-effect-atom (atom 0))
 
 (deftest test-cached-subscriptions
-  (subs/clear-all-handlers!)
   (reset! side-effect-atom 0)
 
   (re-frame/reg-sub-raw
@@ -106,8 +101,6 @@
 ;============== test register-pure macros ================
 
 (deftest test-reg-sub-macro
-  (subs/clear-all-handlers!)
-
   (subs/reg-sub
     :test-sub
     (fn [db [_]] db))
@@ -118,8 +111,6 @@
     (is (= 1 @test-sub))))
 
 (deftest test-reg-sub-macro-singleton
-  (subs/clear-all-handlers!)
-
   (subs/reg-sub
     :a-sub
     (fn [db [_]] (:a db)))
@@ -138,8 +129,6 @@
     (is (= {:a 1} @test-sub))))
 
 (deftest test-reg-sub-macro-vector
-  (subs/clear-all-handlers!)
-
   (subs/reg-sub
     :a-sub
     (fn [db [_]] (:a db)))
@@ -163,8 +152,6 @@
     (is (= {:a 1 :b 3} @test-sub))))
 
 (deftest test-reg-sub-macro-map
-  (subs/clear-all-handlers!)
-
   (subs/reg-sub
     :a-sub
     (fn [db [_]] (:a db)))
@@ -188,8 +175,6 @@
     (is (= {:a 1 :b 3} @test-sub))))
 
 (deftest test-sub-macro-parameters
-  (subs/clear-all-handlers!)
-
   (subs/reg-sub
     :test-sub
     (fn [db [_ b]] [(:a db) b]))
@@ -199,8 +184,6 @@
     (is (= [1 :c] @test-sub))))
 
 (deftest test-sub-macros-chained-parameters
-  (subs/clear-all-handlers!)
-
   (subs/reg-sub
     :a-sub
     (fn [db [_ a]] [(:a db) a]))
@@ -222,8 +205,6 @@
 
 (deftest test-sub-macros-<-
   "test the syntactial sugar"
-  (subs/clear-all-handlers!)
-
   (subs/reg-sub
     :a-sub
     (fn [db [_]] (:a db)))
@@ -239,8 +220,6 @@
 
 (deftest test-sub-macros-chained-parameters-<-
   "test the syntactial sugar"
-  (subs/clear-all-handlers!)
-
   (subs/reg-sub
     :a-sub
     (fn [db [_]] (:a db)))
@@ -260,7 +239,6 @@
     (is (= {:a 1 :b 2} @test-sub) )))
 
 (deftest test-registering-subs-doesnt-create-subscription
-  (subs/clear-all-handlers!)
   (let [sub-called? (atom false)]
     (with-redefs [subs/subscribe (fn [& args] (reset! sub-called? true))]
       (subs/reg-sub