Source value can be nil to remove rendered component.

Previously only the initial value of a live component's source could
be nil and a placeholder will be rendered instead of the component.

Now the source value can change back to nil and the component will be
replaced with a placeholder.

This is because we aren't using go blocks as the conveyence mechanism anymore.

README.md

@@ -102,6 +102,9 @@ see namespace docstring for an integration source in `ripley.integration.<type>`
 
 ## Changes
 
+### 2023-06-28
+- Source value can be `nil` now and component is replaced with placeholder
+
 ### 2023-06-10
 - Support client side success and failure callbacks
 

src/ripley/html.clj

@@ -396,6 +396,15 @@
   `(let ~bindings
      ~(compile-html body)))
 
+(defn wrap-placeholder [component-fn]
+  (fn [value]
+    (if (some? value)
+      (component-fn value)
+      (let [id (dynamic/consume-component-id!)]
+        (out! "<script type=\"ripley/placeholder\" data-rl=\""
+              id
+              "\"></script>")))))
+
 (defn compile-live
   "Compile special :ripley.html/live element."
   [live-element]
@@ -413,7 +422,7 @@
            ~comp-sym ~(or component
                           `(fn [thing#]
                              (out! (str thing#))))
-           ~id-sym (p/register! dynamic/*live-context* ~source-sym ~comp-sym
+           ~id-sym (p/register! dynamic/*live-context* ~source-sym (wrap-placeholder ~comp-sym)
                                 ~(merge
                                   {}
                                   (when patch

src/ripley/live/context.clj

@@ -65,7 +65,7 @@
       (p/close! source)
 
       :else
-      (when (and update? (some? val)) ;; PENDING: allow nil as value now that we are not using channels
+      (when update?
         (let [target-id (if (patch/target-parent? patch)
                           parent
                           id)