From 4ff3f04436e4a2b3d49f57cf25643c94ed4b39a4 Mon Sep 17 00:00:00 2001
From: Vincent Latombe <vincent@latombe.net>
Date: Wed, 7 Oct 2020 14:37:32 +0200
Subject: [PATCH] [JENKINS-63828] It is legal to have a
 CloudProvisioningListener not implementing canProvision

I got confused in
https://github.com/jenkinsci/jenkins/commit/3992a30efb1abf697cae8e02f9e81dd04b92b135
by Cloud#canProvision which was abstract vs.
CloudProvisioningListener#canProvision which wasn't and was returning
null.
---
 core/src/main/java/hudson/Util.java           |  2 +-
 .../slaves/CloudProvisioningListener.java     |  9 +++++---
 core/src/test/java/hudson/UtilTest.java       |  2 +-
 .../slaves/CloudProvisioningListenerTest.java | 21 +++++++++----------
 4 files changed, 18 insertions(+), 16 deletions(-)

diff --git a/core/src/main/java/hudson/Util.java b/core/src/main/java/hudson/Util.java
index 6db16d5b04..0b24f7713f 100644
--- a/core/src/main/java/hudson/Util.java
+++ b/core/src/main/java/hudson/Util.java
@@ -1480,7 +1480,7 @@ public class Util {
         if (isOverridden(base, derived, methodName, types)) {
             return supplier.get();
         } else {
-            throw new AbstractMethodError("You must override at least one of the "
+            throw new AbstractMethodError("The class " + derived.getName() + " must override at least one of the "
                     + base.getSimpleName() + "." + methodName + " methods");
         }
     }
diff --git a/core/src/main/java/hudson/slaves/CloudProvisioningListener.java b/core/src/main/java/hudson/slaves/CloudProvisioningListener.java
index 7eaa77a1f5..2f27a49604 100644
--- a/core/src/main/java/hudson/slaves/CloudProvisioningListener.java
+++ b/core/src/main/java/hudson/slaves/CloudProvisioningListener.java
@@ -42,13 +42,16 @@ public abstract class CloudProvisioningListener implements ExtensionPoint {
      */
     @Deprecated
     public CauseOfBlockage canProvision(Cloud cloud, Label label, int numExecutors) {
-        return Util.ifOverridden(() -> canProvision(cloud, new CloudState(label, 0), numExecutors),
-                CloudProvisioningListener.class,
+        if (Util.isOverridden(CloudProvisioningListener.class,
                 getClass(),
                 "canProvision",
                 Cloud.class,
                 CloudState.class,
-                int.class);
+                int.class)) {
+            return canProvision(cloud, new CloudState(label, 0), numExecutors);
+        } else {
+            return null;
+        }
     }
 
     /**
diff --git a/core/src/test/java/hudson/UtilTest.java b/core/src/test/java/hudson/UtilTest.java
index 87a454f573..7beb38e97b 100644
--- a/core/src/test/java/hudson/UtilTest.java
+++ b/core/src/test/java/hudson/UtilTest.java
@@ -598,7 +598,7 @@ public class UtilTest {
         AbstractMethodError error = Assert.assertThrows(AbstractMethodError.class, () -> {
             Util.ifOverridden(() -> true, BaseClass.class, DerivedClassFailure.class, "method");
         });
-        assertEquals("You must override at least one of the BaseClass.method methods", error.getMessage());
+        assertEquals("The class " + DerivedClassFailure.class.getName() + " must override at least one of the BaseClass.method methods", error.getMessage());
     }
 
     public static class BaseClass {
diff --git a/core/src/test/java/hudson/slaves/CloudProvisioningListenerTest.java b/core/src/test/java/hudson/slaves/CloudProvisioningListenerTest.java
index 46b8378527..641706f887 100644
--- a/core/src/test/java/hudson/slaves/CloudProvisioningListenerTest.java
+++ b/core/src/test/java/hudson/slaves/CloudProvisioningListenerTest.java
@@ -1,37 +1,36 @@
 package hudson.slaves;
 
+import hudson.model.Messages;
 import hudson.model.queue.CauseOfBlockage;
-import org.junit.Assert;
 import org.junit.Test;
 import org.jvnet.hudson.test.Issue;
+import org.jvnet.localizer.Localizable;
 
 import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertNull;
 
 public class CloudProvisioningListenerTest {
-    public static class CloudProvisioningListenerFailing extends CloudProvisioningListener {}
+    public static class CloudProvisioningListenerNoOverride extends CloudProvisioningListener {}
 
-    public static class CloudProvisioningListenerSuccess extends CloudProvisioningListener {
+    public static class CloudProvisioningListenerOverride extends CloudProvisioningListener {
         @Override
         public CauseOfBlockage canProvision(Cloud cloud, Cloud.CloudState state, int numExecutors) {
-            return null;
+            return CauseOfBlockage.fromMessage(Messages._Queue_InProgress());
         }
     }
 
     @Issue("JENKINS-63828")
     @Test
-    public void failing(){
+    public void noOverride(){
         Cloud.CloudState state = new Cloud.CloudState(null, 0);
-        AbstractMethodError error = Assert.assertThrows(AbstractMethodError.class, () -> {
-            new CloudProvisioningListenerFailing().canProvision(null, state, 0);
-        });
-        assertEquals("You must override at least one of the CloudProvisioningListener.canProvision methods", error.getMessage());
+        assertNull(new CloudProvisioningListenerNoOverride().canProvision(null, state, 0));
     }
 
     @Issue("JENKINS-63828")
     @Test
-    public void success() {
+    public void override() {
         Cloud.CloudState state = new Cloud.CloudState(null, 0);
-        assertNull(new CloudProvisioningListenerSuccess().canProvision(null, state, 0));
+        assertNotNull(new CloudProvisioningListenerOverride().canProvision(null, state, 0));
     }
 }