From c8c8fa5a29ac7c4e724b38756932c26aaf3cdece Mon Sep 17 00:00:00 2001
From: Jesse Glick <jglick@cloudbees.com>
Date: Tue, 8 Oct 2024 15:42:24 -0400
Subject: [PATCH 1/2] `Job.BuildNumberAssigner`

---
 core/src/main/java/hudson/model/Job.java | 48 +++++++++++++++++++++---
 1 file changed, 43 insertions(+), 5 deletions(-)

diff --git a/core/src/main/java/hudson/model/Job.java b/core/src/main/java/hudson/model/Job.java
index e4d54d44b375..36bd9407e7d4 100644
--- a/core/src/main/java/hudson/model/Job.java
+++ b/core/src/main/java/hudson/model/Job.java
@@ -34,6 +34,7 @@
 import hudson.BulkChange;
 import hudson.EnvVars;
 import hudson.Extension;
+import hudson.ExtensionList;
 import hudson.ExtensionPoint;
 import hudson.FeedAdapter;
 import hudson.PermalinkList;
@@ -346,12 +347,49 @@ public boolean isKeepDependencies() {
     }
 
     /**
-     * Allocates a new buildCommand number.
+     * Allocates a new build number.
+     * @see BuildNumberAssigner
      */
-    public synchronized int assignBuildNumber() throws IOException {
-        int r = nextBuildNumber++;
-        saveNextBuildNumber();
-        return r;
+    public int assignBuildNumber() throws IOException {
+        var bna = ExtensionList.lookupFirst(BuildNumberAssigner.class).assignBuildNumber(this);
+        if (bna.needsSave) {
+            saveNextBuildNumber();
+        }
+        return bna.assignedNumber;
+    }
+
+    /**
+     * Alternate strategy for assigning build numbers.
+     * @see #assignBuildNumber()
+     */
+    @Restricted(Beta.class)
+    public interface BuildNumberAssigner extends ExtensionPoint {
+        /**
+         * Strategy outcome.
+         * @param assignedNumber the return value for {@link #assignBuildNumber()}
+         * @param needsSave whether {@link #saveNextBuildNumber} should be called afterwards
+         */
+        record BuildNumberAssignment(int assignedNumber, boolean needsSave) {};
+
+        /**
+         * Assign a unique number for a new build of a given job.
+         * @see #getNextBuildNumber
+         * @see #fastUpdateNextBuildNumber
+         */
+        BuildNumberAssignment assignBuildNumber(Job<?, ?> job) throws IOException;
+    }
+
+    @Restricted(DoNotUse.class)
+    @Extension(ordinal = -1000)
+    public static final class DefaultBuildNumberAssigner implements BuildNumberAssigner {
+        @Override
+        public BuildNumberAssignment assignBuildNumber(Job<?, ?> job) throws IOException {
+            synchronized (job) {
+                int r = job.nextBuildNumber++;
+                job.saveNextBuildNumber();
+                return new BuildNumberAssignment(r, false);
+            }
+        }
     }
 
     /**

From b73a0c5baefdf63e9f153ed137f7ceb66d3562eb Mon Sep 17 00:00:00 2001
From: Jesse Glick <jglick@cloudbees.com>
Date: Wed, 9 Oct 2024 10:21:32 -0400
Subject: [PATCH 2/2] Clearer API for `saveNextBuildNumber`
 https://github.com/jenkinsci/jenkins/pull/9846#discussion_r1792991572

---
 core/src/main/java/hudson/model/Job.java | 29 +++++++++---------------
 1 file changed, 11 insertions(+), 18 deletions(-)

diff --git a/core/src/main/java/hudson/model/Job.java b/core/src/main/java/hudson/model/Job.java
index 36bd9407e7d4..a393e33c9a6b 100644
--- a/core/src/main/java/hudson/model/Job.java
+++ b/core/src/main/java/hudson/model/Job.java
@@ -351,43 +351,36 @@ public boolean isKeepDependencies() {
      * @see BuildNumberAssigner
      */
     public int assignBuildNumber() throws IOException {
-        var bna = ExtensionList.lookupFirst(BuildNumberAssigner.class).assignBuildNumber(this);
-        if (bna.needsSave) {
-            saveNextBuildNumber();
-        }
-        return bna.assignedNumber;
+        return ExtensionList.lookupFirst(BuildNumberAssigner.class).assignBuildNumber(this, this::saveNextBuildNumber);
     }
 
     /**
      * Alternate strategy for assigning build numbers.
-     * @see #assignBuildNumber()
      */
     @Restricted(Beta.class)
     public interface BuildNumberAssigner extends ExtensionPoint {
         /**
-         * Strategy outcome.
-         * @param assignedNumber the return value for {@link #assignBuildNumber()}
-         * @param needsSave whether {@link #saveNextBuildNumber} should be called afterwards
+         * Implementation of {@link Job#assignBuildNumber}.
          */
-        record BuildNumberAssignment(int assignedNumber, boolean needsSave) {};
-
+        int assignBuildNumber(Job<?, ?> job, SaveNextBuildNumber saveNextBuildNumber) throws IOException;
         /**
-         * Assign a unique number for a new build of a given job.
-         * @see #getNextBuildNumber
-         * @see #fastUpdateNextBuildNumber
+         * Provides an externally accessible alias for {@link Job#saveNextBuildNumber}, which is {@code protected}.
+         * ({@link #getNextBuildNumber} and {@link #fastUpdateNextBuildNumber} are already accessible.)
          */
-        BuildNumberAssignment assignBuildNumber(Job<?, ?> job) throws IOException;
+        interface SaveNextBuildNumber {
+            void call() throws IOException;
+        }
     }
 
     @Restricted(DoNotUse.class)
     @Extension(ordinal = -1000)
     public static final class DefaultBuildNumberAssigner implements BuildNumberAssigner {
         @Override
-        public BuildNumberAssignment assignBuildNumber(Job<?, ?> job) throws IOException {
+        public int assignBuildNumber(Job<?, ?> job, SaveNextBuildNumber saveNextBuildNumber) throws IOException {
             synchronized (job) {
                 int r = job.nextBuildNumber++;
-                job.saveNextBuildNumber();
-                return new BuildNumberAssignment(r, false);
+                saveNextBuildNumber.call();
+                return r;
             }
         }
     }