From 00f52b96e6464af142c658ab05a697276b07ae49 Mon Sep 17 00:00:00 2001
From: Simon Cooper <simon.cooper@elastic.co>
Date: Wed, 8 Jan 2025 14:56:04 +0000
Subject: [PATCH] Fix test, and update javadoc

---
 .../org/elasticsearch/features/FeatureSpecification.java  | 8 +++++++-
 .../autosharding/DataStreamAutoShardingServiceTests.java  | 6 +++++-
 2 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/server/src/main/java/org/elasticsearch/features/FeatureSpecification.java b/server/src/main/java/org/elasticsearch/features/FeatureSpecification.java
index c37bc4488f109..2f016349e5fce 100644
--- a/server/src/main/java/org/elasticsearch/features/FeatureSpecification.java
+++ b/server/src/main/java/org/elasticsearch/features/FeatureSpecification.java
@@ -20,8 +20,14 @@
  * unless they also support that feature (this is known as the 'feature ratchet').
  * So once a feature is supported by a cluster, it will always be supported by that cluster in the future.
  * <p>
+ * The only situation where features can be removed is on a compatibility boundary (normally a new major version).
+ * Because a new major version can only form a cluster with the highest minor of the previous major,
+ * any features introduced before that point can be assumed to always be present on that cluster.
+ * The feature itself can be removed by marking it as assumed by {@link NodeFeature#assumedAfterNextCompatibilityBoundary()},
+ * in the last minor, and then removing it and associated conditions in the new major version.
+ * <p>
  * The feature information in cluster state should not normally be directly accessed.
- * All feature checks should be done through {@code FeatureService} to ensure that Elasticsearch's
+ * All feature checks should be done through {@link FeatureService} to ensure that Elasticsearch's
  * guarantees on the introduction of new functionality are followed;
  * that is, new functionality is not enabled until all nodes in the cluster support it.
  * <p>
diff --git a/server/src/test/java/org/elasticsearch/action/datastreams/autosharding/DataStreamAutoShardingServiceTests.java b/server/src/test/java/org/elasticsearch/action/datastreams/autosharding/DataStreamAutoShardingServiceTests.java
index ba0f04d174f43..3a43a1df9bf88 100644
--- a/server/src/test/java/org/elasticsearch/action/datastreams/autosharding/DataStreamAutoShardingServiceTests.java
+++ b/server/src/test/java/org/elasticsearch/action/datastreams/autosharding/DataStreamAutoShardingServiceTests.java
@@ -144,7 +144,11 @@ public Set<NodeFeature> getFeatures() {
 
         {
             // cluster doesn't have feature
-            ClusterState stateNoFeature = ClusterState.builder(ClusterName.DEFAULT).metadata(Metadata.builder()).build();
+            ClusterState stateNoFeature = ClusterState.builder(ClusterName.DEFAULT)
+                .nodes(DiscoveryNodes.builder().add(DiscoveryNodeUtils.create("n1")).add(DiscoveryNodeUtils.create("n2")))
+                .nodeFeatures(Map.of("n1", Set.of(), "n2", Set.of()))
+                .metadata(Metadata.builder())
+                .build();
 
             Settings settings = Settings.builder().put(DataStreamAutoShardingService.DATA_STREAMS_AUTO_SHARDING_ENABLED, true).build();
             DataStreamAutoShardingService noFeatureService = new DataStreamAutoShardingService(