middleware/debug: Log a single line if app-db not changed by a handler

middleware/debug logs a group to the console even if there has been no
change to app-db. This makes it harder to tell if you've made a mistake
in refactoring, as the same log message will be shown whether or not
app-db is changing.

This change will log a single line if app-db is not changed by a handler

Fixes #166

CHANGES.md

@@ -1,3 +1,8 @@
+## Unreleased
+
+Improvements
+  - `debug` middleware logs a single log line instead of a group if there is no difference in app-db between before and after running the handler.
+
 ## 0.7.0  (2016-03-14)
 
 Breaking:

src/re_frame/middleware.cljs

@@ -47,11 +47,14 @@
     [db v]
     (log "Handling re-frame event: " v)
     (let [new-db  (handler db v)
-          diff    (data/diff db new-db)]
+          [before after] (data/diff db new-db)
-      (group "clojure.data/diff for: " v)
+          db-changed? (or (some? before) (some? after))]
-        (log "only before: " (first diff))
+      (if db-changed?
-        (log "only after : " (second diff))
+        (do (group "clojure.data/diff for: " v
-      (groupEnd)
+              (log "only before: " before)
+              (log "only after : " after))
+            (groupEnd))
+        (log "clojure.data/diff no changes for: " v))
       new-db)))