DeprecationInfoAction refactoring (elastic#121181) (elastic#121638)

This refactoring was motivated by the following issues with the current
state of the code:

- The `TransformDeprecationChecker` is listed as plugin checker, but later we remove is from the `plugin_settings` and add it to the `cluster_settings`. This made me consider that the checker might be dealing with transform deprecation warnings but if they are listed under the `cliuster_settings`, it fits better to be part of `ClusterDeprecationChecker`.
- The `DeprecationInfo` is a data class, but it has a method `from` which constructs an `DeprecationInfo.Response` instance. However, this is not a simple factory class but it actually runs all the checks and it also tries to assert that it is not executed on a transport thread. Considering this, I thought it might fit better to the `TransportDeprecationInfoAction`, this way all the logic is in one place and all the checkers are wired and used in the same class.
- Constructing the node settings deprecation issues requires to merge the deprecation warnings of the individual nodes. We considered bringing together the execution of the remote request and the construction of the response in a new class called `NodeDeprecationChecker` that resembles the patterns of the other Checker classes.
- Reinstated the `PLUGIN_CHECKERS` even if we have only one check, so other developers can easier add their plugin checks.
- Finally, we noticed that the way we synthesise the remote requests is difficult to read and maintain because each call is nested under the previous one. We propose in this PR a different pattern that uses the `RefCountingListener` to combine the different remote calls and store their results in a container class named `PrecomputedData`
- **Bonus**: Removed the `LegacyIndexTemplateDeprecationChecker.java` which was not used.

Author: gmarouli

qa/rolling-upgrade/src/javaRestTest/java/org/elasticsearch/upgrades/SourceModeRollingUpgradeIT.java

@@ -18,7 +18,6 @@
 import java.util.List;
 import java.util.Map;
 
-import static org.hamcrest.Matchers.containsString;
 import static org.hamcrest.Matchers.equalTo;
 
 public class SourceModeRollingUpgradeIT extends AbstractRollingUpgradeTestCase {
@@ -83,20 +82,10 @@ public void testConfigureStoredSourceWhenIndexIsCreatedLegacy() throws IOExcepti
     private void assertDeprecationWarningForTemplate(String templateName) throws IOException {
         var request = new Request("GET", "/_migration/deprecations");
         var response = entityAsMap(client().performRequest(request));
-        if (response.containsKey("templates")) {
-            // Check the newer version of the deprecation API that contains the templates section
-            Map<?, ?> issuesByTemplate = (Map<?, ?>) response.get("templates");
-            assertThat(issuesByTemplate.containsKey(templateName), equalTo(true));
-            var templateIssues = (List<?>) issuesByTemplate.get(templateName);
-            assertThat(((Map<?, ?>) templateIssues.getFirst()).get("message"), equalTo(SourceFieldMapper.DEPRECATION_WARNING));
-        } else {
-            // Bwc version with 8.18 until https://github.com/elastic/elasticsearch/pull/120505/ gets backported, clean up after backport
-            var nodeSettings = (Map<?, ?>) ((List<?>) response.get("node_settings")).getFirst();
-            assertThat(nodeSettings.get("message"), equalTo(SourceFieldMapper.DEPRECATION_WARNING));
-            assertThat(
-                (String) nodeSettings.get("details"),
-                containsString(SourceFieldMapper.DEPRECATION_WARNING + " Affected component templates: [" + templateName + "]")
-            );
-        }
+        assertThat(response.containsKey("templates"), equalTo(true));
+        Map<?, ?> issuesByTemplate = (Map<?, ?>) response.get("templates");
+        assertThat(issuesByTemplate.containsKey(templateName), equalTo(true));
+        var templateIssues = (List<?>) issuesByTemplate.get(templateName);
+        assertThat(((Map<?, ?>) templateIssues.getFirst()).get("message"), equalTo(SourceFieldMapper.DEPRECATION_WARNING));
     }
 }

x-pack/plugin/deprecation/src/main/java/module-info.java

@@ -13,6 +13,7 @@
     requires org.apache.logging.log4j;
     requires org.apache.logging.log4j.core;
     requires log4j2.ecs.layout;
+    requires org.apache.lucene.core;
 
     exports org.elasticsearch.xpack.deprecation to org.elasticsearch.server;
     exports org.elasticsearch.xpack.deprecation.logging to org.elasticsearch.server;

x-pack/plugin/deprecation/src/main/java/org/elasticsearch/xpack/deprecation/ClusterDeprecationChecker.java

@@ -0,0 +1,56 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License
+ * 2.0; you may not use this file except in compliance with the Elastic License
+ * 2.0.
+ */
+
+package org.elasticsearch.xpack.deprecation;
+
+import org.apache.logging.log4j.LogManager;
+import org.apache.logging.log4j.Logger;
+import org.elasticsearch.cluster.ClusterState;
+import org.elasticsearch.common.TriConsumer;
+import org.elasticsearch.xcontent.NamedXContentRegistry;
+import org.elasticsearch.xpack.core.deprecation.DeprecationIssue;
+import org.elasticsearch.xpack.core.transform.transforms.TransformConfig;
+
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * Cluster-specific deprecation checks, this is used to populate the {@code cluster_settings} field
+ */
+public class ClusterDeprecationChecker {
+
+    private static final Logger logger = LogManager.getLogger(ClusterDeprecationChecker.class);
+    private final List<TriConsumer<ClusterState, List<TransformConfig>, List<DeprecationIssue>>> CHECKS = List.of(
+        this::checkTransformSettings
+    );
+    private final NamedXContentRegistry xContentRegistry;
+
+    ClusterDeprecationChecker(NamedXContentRegistry xContentRegistry) {
+        this.xContentRegistry = xContentRegistry;
+    }
+
+    public List<DeprecationIssue> check(ClusterState clusterState, List<TransformConfig> transformConfigs) {
+        List<DeprecationIssue> allIssues = new ArrayList<>();
+        CHECKS.forEach(check -> check.apply(clusterState, transformConfigs, allIssues));
+        return allIssues;
+    }
+
+    private void checkTransformSettings(
+        ClusterState clusterState,
+        List<TransformConfig> transformConfigs,
+        List<DeprecationIssue> allIssues
+    ) {
+        for (var config : transformConfigs) {
+            try {
+                allIssues.addAll(config.checkForDeprecations(xContentRegistry));
+            } catch (IOException e) {
+                logger.warn("failed to check transformation settings for '" + config.getId() + "'", e);
+            }
+        }
+    }
+}

x-pack/plugin/deprecation/src/main/java/org/elasticsearch/xpack/deprecation/DataStreamDeprecationChecker.java

@@ -18,13 +18,13 @@
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.Objects;
 import java.util.Set;
 import java.util.function.BiFunction;
 import java.util.stream.Collectors;
 
 import static java.util.Map.entry;
 import static java.util.Map.ofEntries;
-import static org.elasticsearch.xpack.deprecation.DeprecationInfoAction.filterChecks;
 
 /**
  * Checks the data streams for deprecation warnings.
@@ -44,10 +44,24 @@ public DataStreamDeprecationChecker(IndexNameExpressionResolver indexNameExpress
 
     /**
      * @param clusterState The cluster state provided for the checker
+     * @param request not used yet in these checks
+     * @param precomputedData not used yet in these checks
      * @return the name of the data streams that have violated the checks with their respective warnings.
      */
     @Override
-    public Map<String, List<DeprecationIssue>> check(ClusterState clusterState, DeprecationInfoAction.Request request) {
+    public Map<String, List<DeprecationIssue>> check(
+        ClusterState clusterState,
+        DeprecationInfoAction.Request request,
+        TransportDeprecationInfoAction.PrecomputedData precomputedData
+    ) {
+        return check(clusterState);
+    }
+
+    /**
+     * @param clusterState The cluster state provided for the checker
+     * @return the name of the data streams that have violated the checks with their respective warnings.
+     */
+    public Map<String, List<DeprecationIssue>> check(ClusterState clusterState) {
         List<String> dataStreamNames = indexNameExpressionResolver.dataStreamNames(
             clusterState,
             IndicesOptions.LENIENT_EXPAND_OPEN_CLOSED_HIDDEN
@@ -58,7 +72,10 @@ public Map<String, List<DeprecationIssue>> check(ClusterState clusterState, Depr
         Map<String, List<DeprecationIssue>> dataStreamIssues = new HashMap<>();
         for (String dataStreamName : dataStreamNames) {
             DataStream dataStream = clusterState.metadata().dataStreams().get(dataStreamName);
-            List<DeprecationIssue> issuesForSingleDataStream = filterChecks(DATA_STREAM_CHECKS, c -> c.apply(dataStream, clusterState));
+            List<DeprecationIssue> issuesForSingleDataStream = DATA_STREAM_CHECKS.stream()
+                .map(c -> c.apply(dataStream, clusterState))
+                .filter(Objects::nonNull)
+                .toList();
             if (issuesForSingleDataStream.isEmpty() == false) {
                 dataStreamIssues.put(dataStreamName, issuesForSingleDataStream);
             }

x-pack/plugin/deprecation/src/main/java/org/elasticsearch/xpack/deprecation/Deprecation.java

@@ -33,7 +33,7 @@
 import java.util.function.Predicate;
 import java.util.function.Supplier;
 
-import static org.elasticsearch.xpack.deprecation.DeprecationChecks.SKIP_DEPRECATIONS_SETTING;
+import static org.elasticsearch.xpack.deprecation.TransportDeprecationInfoAction.SKIP_DEPRECATIONS_SETTING;
 import static org.elasticsearch.xpack.deprecation.logging.DeprecationIndexingComponent.DEPRECATION_INDEXING_FLUSH_INTERVAL;
 
 /**