Recommend to Maven users to enable the Maven extensions for the Quarkus plugin

Author: Sanne

devtools/maven/src/main/java/io/quarkus/maven/QuarkusBootstrapMojo.java

@@ -175,6 +175,7 @@ public abstract class QuarkusBootstrapMojo extends AbstractMojo {
 
     @Override
     public void execute() throws MojoExecutionException, MojoFailureException {
+        hintEnableExtensions();
         if (!beforeExecute()) {
             return;
         }
@@ -199,6 +200,22 @@ public void execute() throws MojoExecutionException, MojoFailureException {
         }
     }
 
+    private void hintEnableExtensions() {
+        if (!bootstrapSessionListener.isEnabled()) {
+            super.getLog().warn("The Maven extensions for the Quarkus Maven plugin are not enabled for this build. " +
+                    "We recommend enabling this, so that the plugin can verify essential build settings have been configured as required. "
+                    +
+                    "Please enable by adding \"<extensions>true</extensions>\" in your quarkus-maven-plugin declaration; it should look like:\n"
+                    +
+                    "\n\t<plugin>\n" +
+                    "\t\t<groupId>${quarkus.platform.group-id}</groupId>\n" +
+                    "\t\t<artifactId>quarkus-maven-plugin</artifactId>\n" +
+                    "\t\t<version>${quarkus.platform.version}</version>\n" +
+                    "\t\t<extensions>true</extensions> <!-- THIS ONE -->\n" +
+                    "\t\t...\n");
+        }
+    }
+
     @Override
     public void setLog(Log log) {
         super.setLog(log);