Hook for VertxBuilder customization

Given methods like TracingOptions#setTracer have been deprecated, a new hook can help users configure the Vert.x instance.

Signed-off-by: Thomas Segismont <tsegismont@gmail.com>

src/main/java/io/vertx/core/impl/launcher/VertxLifecycleHooks.java

@@ -14,7 +14,9 @@
 import io.vertx.core.DeploymentOptions;
 import io.vertx.core.Vertx;
 import io.vertx.core.VertxOptions;
+import io.vertx.core.impl.VertxBuilder;
 import io.vertx.core.json.JsonObject;
+import io.vertx.core.spi.tracing.VertxTracer;
 
 /**
  * Interface that let sub-classes of launcher to be notified on different events.
@@ -31,6 +33,18 @@ public interface VertxLifecycleHooks {
    */
   void afterConfigParsed(JsonObject config);
 
+  /**
+   * Default implementation for the {@link VertxBuilder} creation.
+   * <p>
+   * This can be overridden in order to customize, for example, the tracer, with {@link VertxBuilder#tracer(VertxTracer)}.
+   *
+   * @param config the Vert.x options to use, in JSON format
+   * @return the Vert.x builder instance
+   */
+  default VertxBuilder createVertxBuilder(JsonObject config) {
+    return config == null ? new VertxBuilder() : new VertxBuilder(config);
+  }
+
   /**
    * Hook for sub-classes of the {@link io.vertx.core.Launcher} class before the vertx instance is started. Options
    * can still be updated.

src/main/java/io/vertx/core/impl/launcher/commands/BareCommand.java

@@ -201,15 +201,8 @@ public void run(Runnable action) {
   protected Vertx startVertx() {
     JsonObject optionsJson = getJsonFromFileOrString(vertxOptions, "options");
 
-    EventBusOptions eventBusOptions;
-    VertxBuilder builder;
-    if (optionsJson == null) {
-      eventBusOptions = getEventBusOptions();
-      builder = new VertxBuilder();
-    } else {
-      eventBusOptions = getEventBusOptions(optionsJson.getJsonObject("eventBusOptions"));
-      builder = new VertxBuilder(optionsJson);
-    }
+    EventBusOptions eventBusOptions = optionsJson == null ? getEventBusOptions() : getEventBusOptions(optionsJson.getJsonObject("eventBusOptions"));
+    VertxBuilder builder = createVertxBuilder(optionsJson);
     options = builder.options();
     options.setEventBusOptions(eventBusOptions);
 
@@ -338,6 +331,14 @@ protected void beforeStartingVertx(VertxOptions options) {
     }
   }
 
+  protected VertxBuilder createVertxBuilder(JsonObject config) {
+    Object main = executionContext.main();
+    if (main instanceof VertxLifecycleHooks) {
+      return ((VertxLifecycleHooks) main).createVertxBuilder(config);
+    }
+    return new VertxBuilder(config);
+  }
+
   /**
    * @return the event bus options.
    */