jolshan commented on code in PR #15685:
URL: https://github.com/apache/kafka/pull/15685#discussion_r1610250283


##########
server-common/src/main/java/org/apache/kafka/server/common/Features.java:
##########
@@ -16,72 +16,135 @@
  */
 package org.apache.kafka.server.common;
 
-import java.util.Collections;
-import java.util.HashMap;
+import java.util.Arrays;
+import java.util.Iterator;
+import java.util.List;
 import java.util.Map;
-import java.util.Objects;
+import java.util.stream.Collectors;
 
-import static org.apache.kafka.server.common.MetadataVersion.FEATURE_NAME;
+/**
+ * This is enum for the various features implemented for Kafka clusters.
+ * KIP-584: Versioning Scheme for Features introduced the idea of various 
features, but only added one feature -- MetadataVersion.
+ * KIP-1022: Formatting and Updating Features allowed for more features to be 
added. In order to set and update features,
+ * they need to be specified via the StorageTool or FeatureCommand tools.
+ * <br>
+ * Having a unified enum for the features that will use a shared type in the 
API used to set and update them
+ * makes it easier to process these features.
+ */
+public enum Features {
+
+    /**
+     * Features defined. If a feature is included in this list, and marked to 
be used in production they will also be specified when
+     * formatting a cluster via the StorageTool. MetadataVersion is handled 
separately, so it is not included here.
+     *
+     * See {@link TestFeatureVersion} as an example. See {@link 
FeatureVersion} when implementing a new feature.
+     */
+    TEST_VERSION("test.feature.version", TestFeatureVersion.values(), 
TestFeatureVersion::fromFeatureLevel, false);
 
-public final class Features {
-    private final MetadataVersion version;
-    private final Map<String, Short> finalizedFeatures;
-    private final long finalizedFeaturesEpoch;
+    public static final Features[] FEATURES;
+    public static final List<Features> PRODUCTION_FEATURES;
+    private final String name;
+    private final FeatureVersion[] features;
+    private final CreateMethod createFeatureVersionMethod;
+    private final boolean usedInProduction;
 
-    public static Features fromKRaftVersion(MetadataVersion version) {
-        return new Features(version, Collections.emptyMap(), -1, true);
+    Features(String name,
+             FeatureVersion[] features,
+             CreateMethod createMethod,
+             boolean usedInProduction) {
+        this.name = name;
+        this.features = features;
+        this.createFeatureVersionMethod = createMethod;
+        this.usedInProduction = usedInProduction;
     }
 
-    public Features(
-        MetadataVersion version,
-        Map<String, Short> finalizedFeatures,
-        long finalizedFeaturesEpoch,
-        boolean kraftMode
-    ) {
-        this.version = version;
-        this.finalizedFeatures = new HashMap<>(finalizedFeatures);
-        this.finalizedFeaturesEpoch = finalizedFeaturesEpoch;
-        // In KRaft mode, we always include the metadata version in the 
features map.
-        // In ZK mode, we never include it.
-        if (kraftMode) {
-            this.finalizedFeatures.put(FEATURE_NAME, version.featureLevel());
-        } else {
-            this.finalizedFeatures.remove(FEATURE_NAME);
-        }
+    static {
+        Features[] enumValues = Features.values();
+        FEATURES = Arrays.copyOf(enumValues, enumValues.length);
+
+        PRODUCTION_FEATURES = Arrays.stream(FEATURES).filter(feature ->
+                feature.usedInProduction).collect(Collectors.toList());
     }
 
-    public MetadataVersion metadataVersion() {
-        return version;
+    public String featureName() {
+        return name;
     }
 
-    public Map<String, Short> finalizedFeatures() {
-        return finalizedFeatures;
+    public FeatureVersion[] features() {
+        return features;
     }
 
-    public long finalizedFeaturesEpoch() {
-        return finalizedFeaturesEpoch;
+    /**
+     * Creates a FeatureVersion from a given name and level with the correct 
feature object underneath.
+     *
+     * @param level   the level of the feature
+     * @returns       the FeatureVersionUtils.FeatureVersion for the feature 
the enum is based on.
+     * @throws        IllegalArgumentException if the feature name is not 
valid (not implemented for this method)
+     */
+    public FeatureVersion fromFeatureLevel(short level) {
+        return createFeatureVersionMethod.fromFeatureLevel(level);
     }
 
-    @Override
-    public boolean equals(Object o) {
-        if (o == null || !(o.getClass().equals(Features.class))) return false;
-        Features other = (Features) o;
-        return version == other.version &&
-            finalizedFeatures.equals(other.finalizedFeatures) &&
-                finalizedFeaturesEpoch == other.finalizedFeaturesEpoch;
+    /**
+     * A method to validate the feature can be set. If a given feature relies 
on another feature, the dependencies should be
+     * captured in {@link FeatureVersion#dependencies()}
+     * <p>
+     * For example, say feature X level x relies on feature Y level y:
+     * if feature X >= x then throw an error if feature Y < y.
+     *
+     * All feature levels above 0 require metadata.version=4 (IBP_3_3_IV0) in 
order to write the feature records to the cluster.
+     *
+     * @param feature                   the feature we are validating
+     * @param metadataVersion           the metadata version we have (or want 
to set)
+     * @param features                  the feature versions (besides 
MetadataVersion) we have (or want to set)
+     * @throws IllegalArgumentException if the feature is not valid
+     */
+    public static void validateVersion(FeatureVersion feature, MetadataVersion 
metadataVersion, Map<String, Short> features) {
+        if (feature.featureLevel() >= 1 && 
metadataVersion.isLessThan(MetadataVersion.IBP_3_3_IV0))
+            throw new IllegalArgumentException(feature.featureName() + " could 
not be set to " + feature.featureLevel() +
+                    " because it depends on metadata.version=14 (" + 
MetadataVersion.IBP_3_3_IV0 + ")");

Review Comment:
   yes thank you for catching.



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