XWIKI-17338: Handle getting cached async content with JSX with an AJAX request

  * Add a boolean in AsyncRendererConfiguration to allow forcing to send
    back a placeholder even if the data are available already
  * Use that boolean in the default existing renderer executors to
    return the placeholder if it's forced
  * Consider the execution as async if the placeholder is forced.

xwiki-platform-core/xwiki-platform-rendering/xwiki-platform-rendering-async/xwiki-platform-rendering-async-api/src/main/java/org/xwiki/rendering/async/internal/AsyncRendererConfiguration.java

@@ -40,6 +40,8 @@ public class AsyncRendererConfiguration
 
     protected boolean secureSet;
 
+    protected boolean placeHolderForced;
+
     /**
      * @return the list of context entries to take remember for the execution
      */
@@ -90,4 +92,28 @@ public void setSecureReference(DocumentReference documentReference, DocumentRefe
         this.secureAuthorReference = authorReference;
         this.secureSet = true;
     }
+
+    /**
+     * @return {@code true} if the renderer should display a placeholder even if the data is already available.
+     * @see #setPlaceHolderForced(boolean).
+     * @since 12.5RC1
+     */
+    public boolean isPlaceHolderForced()
+    {
+        return placeHolderForced;
+    }
+
+    /**
+     * Set to {@code true} to force the renderer to return an async placeholder even if the data is available.
+     * This allows to use easily the Async rendering framework with AJAX requests: we can force the async renderers
+     * in an AJAX request to return always placeholders, so they are resolved once added in the current DOM by using
+     * Javascript.
+     *
+     * @param placeHolderForced {@code true} to force using a placeholder.
+     * @since 12.5RC1
+     */
+    public void setPlaceHolderForced(boolean placeHolderForced)
+    {
+        this.placeHolderForced = placeHolderForced;
+    }
 }

xwiki-platform-core/xwiki-platform-rendering/xwiki-platform-rendering-async/xwiki-platform-rendering-async-api/src/main/java/org/xwiki/rendering/async/internal/block/DefaultBlockAsyncRendererExecutor.java

@@ -127,7 +127,7 @@ public Block execute(BlockAsyncRenderer renderer, AsyncRendererConfiguration con
         // Get result
         BlockAsyncRendererResult result = (BlockAsyncRendererResult) response.getStatus().getResult();
 
-        if (result != null) {
+        if (result != null && !configuration.isPlaceHolderForced()) {
             return result.getBlock();
         }
 
@@ -156,7 +156,7 @@ public String render(BlockAsyncRenderer renderer, AsyncRendererConfiguration con
         // Get result
         BlockAsyncRendererResult result = (BlockAsyncRendererResult) response.getStatus().getResult();
 
-        if (result != null) {
+        if (result != null && !configuration.isPlaceHolderForced()) {
             return result.getResult();
         }
 

xwiki-platform-core/xwiki-platform-rendering/xwiki-platform-rendering-async/xwiki-platform-rendering-async-default/src/main/java/org/xwiki/rendering/async/internal/DefaultAsyncRendererExecutor.java

@@ -150,7 +150,9 @@ public AsyncRendererJobStatus getAsyncStatus(List<String> id, String clientId, l
     public AsyncRendererExecutorResponse render(AsyncRenderer renderer, AsyncRendererConfiguration configuration)
         throws JobException, RenderingException
     {
-        boolean asyncAllowed = renderer.isAsyncAllowed() && this.asyncContext.isEnabled();
+        // if placeholder is forced, then we always consider it as async.
+        boolean asyncAllowed = configuration.isPlaceHolderForced()
+                                || (renderer.isAsyncAllowed() && this.asyncContext.isEnabled());
         boolean cacheAllowed = renderer.isCacheAllowed();
 
         // Get context and job id
@@ -167,7 +169,7 @@ public AsyncRendererExecutorResponse render(AsyncRenderer renderer, AsyncRendere
 
                 if (status != null
                     && (status.getEndDate() == null || this.cacheControl.isCacheReadAllowed(status.getEndDate()))) {
-                    if (status.getResult() != null) {
+                    if (status.getResult() != null && !configuration.isPlaceHolderForced()) {
                         // Available cached result, return it
 
                         injectUses(status);