From 9a4a38352952c83a0ba039a7e0ac8959bfc9ca76 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Yoann=20Rodi=C3=A8re?= <yoann@hibernate.org>
Date: Wed, 27 Jul 2022 16:26:58 +0200
Subject: [PATCH] Throw an exception on extension loading if a build step
 doesn't produce anything

---
 core/builder/pom.xml                          |  6 +++++
 .../io/quarkus/builder/BuildStepBuilder.java  |  9 +++++++
 .../java/io/quarkus/builder/BasicTests.java   | 27 +++++++++++++++++++
 3 files changed, 42 insertions(+)

diff --git a/core/builder/pom.xml b/core/builder/pom.xml
index b2160369dbd27..d0cf9c314a729 100644
--- a/core/builder/pom.xml
+++ b/core/builder/pom.xml
@@ -49,6 +49,12 @@
             <artifactId>junit-jupiter</artifactId>
             <scope>test</scope>
         </dependency>
+
+        <dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+            <scope>test</scope>
+        </dependency>
     </dependencies>
 
     <build>
diff --git a/core/builder/src/main/java/io/quarkus/builder/BuildStepBuilder.java b/core/builder/src/main/java/io/quarkus/builder/BuildStepBuilder.java
index 85190c18661b1..254694796a5f6 100644
--- a/core/builder/src/main/java/io/quarkus/builder/BuildStepBuilder.java
+++ b/core/builder/src/main/java/io/quarkus/builder/BuildStepBuilder.java
@@ -194,6 +194,15 @@ public BuildStepBuilder consumes(Class<? extends BuildItem> type, ConsumeFlags f
      */
     public BuildChainBuilder build() {
         final BuildChainBuilder chainBuilder = this.buildChainBuilder;
+        if (produces.isEmpty()) {
+            throw new IllegalArgumentException(
+                    "Build step '" + buildStep.getId()
+                            + "' does not produce any build item and thus will never get executed."
+                            + " Either change the return type of the method to a build item type,"
+                            + " add a parameter of type BuildProducer<[some build item type]>/Consumer<[some build item type]>,"
+                            + " or annotate the method with @Produces."
+                            + " Use @Produce(EmptyBuildItem.class) if you want to always execute this step.");
+        }
         if (BuildChainBuilder.LOG_CONFLICT_CAUSING) {
             chainBuilder.addStep(this, new Exception().getStackTrace());
         } else {
diff --git a/core/builder/src/test/java/io/quarkus/builder/BasicTests.java b/core/builder/src/test/java/io/quarkus/builder/BasicTests.java
index f9efe4c9a36ca..fcece83ea3625 100644
--- a/core/builder/src/test/java/io/quarkus/builder/BasicTests.java
+++ b/core/builder/src/test/java/io/quarkus/builder/BasicTests.java
@@ -1,5 +1,6 @@
 package io.quarkus.builder;
 
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
 import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertNotNull;
 import static org.junit.jupiter.api.Assertions.assertTrue;
@@ -176,6 +177,32 @@ public void execute(final BuildContext context) {
         assertFalse(ran.get());
     }
 
+    @Test
+    public void testMissingProduces() {
+        final BuildChainBuilder builder = BuildChain.builder();
+        BuildStepBuilder stepBuilder = builder.addBuildStep(new BuildStep() {
+            @Override
+            public void execute(final BuildContext context) {
+                context.produce(new DummyItem());
+            }
+
+            @Override
+            public String getId() {
+                return "myBuildStepId";
+            }
+        });
+        stepBuilder.consumes(DummyItem.class);
+        assertThatThrownBy(stepBuilder::build)
+                .isInstanceOf(IllegalArgumentException.class)
+                .hasMessageContainingAll(
+                        "Build step 'myBuildStepId'",
+                        "does not produce any build item and thus will never get executed",
+                        "change the return type of the method to a build item type",
+                        "add a parameter of type BuildProducer<[some build item type]>/Consumer<[some build item type]>",
+                        "annotate the method with @Produces",
+                        "Use @Produce(EmptyBuildItem.class) if you want to always execute this step");
+    }
+
     @Test
     public void testCircular() {
         final BuildChainBuilder builder = BuildChain.builder();