Allow "key" to be specified with meta-data

These are now equivalent
[foo {:key 1}] and
(with-meta [foo] {:key 1})

demo/reagentdemo/news/async.cljs

@@ -59,7 +59,7 @@
             :value @ncolors
             :on-change #(reset! ncolors (-> % .-target .-value))}]])
 
-(defn color-plate [{color :color}]
+(defn color-plate [color]
   [:div.color-plate
    {:style {:background-color color}}])
 
@@ -69,11 +69,12 @@
     [:div
      [:div
       [:p "base color: "]
-      [color-plate {:color (to-rgb color)}]]
+      [color-plate (to-rgb color)]]
      [:div.color-samples
       [:p n " random matching colors:"]
       (map-indexed (fn [k v]
-                     [color-plate {:key k :color v}])
+                     (with-meta [color-plate v]
+                       {:key k}))
                    (take n @random-colors))]]))
 
 (defn color-demo []

src/reagent/impl/template.cljs

@@ -194,18 +194,22 @@
             (set! (.-cljsReactClass tag) (wrap-component tag nil nil))
             (fn-to-class tag)))))))
 
+(defn get-key [x]
+  (when (map? x) (get x :key)))
+
 (defn vec-to-comp [v level]
   (assert (pos? (count v)) "Hiccup form should not be empty")
   (assert (valid-tag? (v 0))
           (str "Invalid Hiccup form: " (pr-str v)))
-  (let [props (get v 1)
-        c (as-class (v 0))
+  (let [c (as-class (v 0))
         jsprops (js-obj cljs-argv v
                         cljs-level level)]
-    (when (map? props)
-      (let [key (:key props)]
-        (when-not (nil? key)
-          (aset jsprops "key" key))))
+    (let [k (-> v meta get-key)
+          k' (if (nil? k)
+               (-> v (get 1) get-key)
+               k)]
+      (when-not (nil? k')
+        (aset jsprops "key" k')))
     (c jsprops)))
 
 (def tmp #js {})