Implement repair functionality for aliases colliding with indices bug

Follow up to elastic#91456 implementing an automated fix for indices corrupted in 8.5.

Author: original-brownbear

server/src/main/java/org/elasticsearch/cluster/metadata/IndexMetadata.java

@@ -8,6 +8,8 @@
 
 package org.elasticsearch.cluster.metadata;
 
+import org.apache.logging.log4j.LogManager;
+import org.apache.logging.log4j.Logger;
 import org.elasticsearch.Version;
 import org.elasticsearch.action.admin.indices.rollover.RolloverInfo;
 import org.elasticsearch.action.support.ActiveShardCount;
@@ -83,6 +85,8 @@
 
 public class IndexMetadata implements Diffable<IndexMetadata>, ToXContentFragment {
 
+    private static final Logger logger = LogManager.getLogger(IndexMetadata.class);
+
     public static final ClusterBlock INDEX_READ_ONLY_BLOCK = new ClusterBlock(
         5,
         "index read-only (api)",
@@ -2140,7 +2144,16 @@ public IndexMetadata build() {
             var aliasesMap = aliases.build();
             for (AliasMetadata alias : aliasesMap.values()) {
                 if (alias.alias().equals(index)) {
-                    throw new IllegalArgumentException("alias name [" + index + "] self-conflicts with index name");
+                    if (indexCreatedVersion.equals(Version.V_8_5_0)) {
+                        var updatedBuilder = ImmutableOpenMap.builder(aliasesMap);
+                        final var brokenAlias = updatedBuilder.remove(index);
+                        final var fixedAlias = AliasMetadata.newAliasMetadata(brokenAlias, index + "-alias-corrupted-by-8-5");
+                        aliasesMap = updatedBuilder.fPut(fixedAlias.getAlias(), fixedAlias).build();
+                        logger.warn("Repaired corrupted alias with the same name as its index for [{}]", index);
+                        break;
+                    } else {
+                        throw new IllegalArgumentException("alias name [" + index + "] self-conflicts with index name");
+                    }
                 }
             }
 

server/src/test/java/org/elasticsearch/cluster/metadata/IndexMetadataTests.java

@@ -47,6 +47,7 @@
 import static org.elasticsearch.cluster.metadata.IndexMetadata.parseIndexNameCounter;
 import static org.hamcrest.Matchers.containsString;
 import static org.hamcrest.Matchers.equalTo;
+import static org.hamcrest.Matchers.hasKey;
 import static org.hamcrest.Matchers.is;
 
 public class IndexMetadataTests extends ESTestCase {
@@ -509,6 +510,16 @@ public void testIndexAndAliasWithSameName() {
         assertEquals("alias name [index] self-conflicts with index name", iae.getMessage());
     }
 
+    public void testRepairIndexAndAliasWithSameName() {
+        final IndexMetadata indexMetadata = IndexMetadata.builder("index")
+            .settings(Settings.builder().put(IndexMetadata.SETTING_VERSION_CREATED, Version.V_8_5_0))
+            .numberOfShards(1)
+            .numberOfReplicas(0)
+            .putAlias(AliasMetadata.builder("index").build())
+            .build();
+        assertThat(indexMetadata.getAliases(), hasKey("index-alias-corrupted-by-8-5"));
+    }
+
     private static Settings indexSettingsWithDataTier(String dataTier) {
         return Settings.builder()
             .put(IndexMetadata.SETTING_VERSION_CREATED, Version.CURRENT)