Fix initialization issue in ElasticsearchException

If a test touches ElasticsearchExceptionHandle before the class
initialzer for ElasticsearchException has run, a circular class
initialization problem can arise. Namely, the class initializer for
ElasticsearchExceptionHandle depends on the class initializer for
ElasticsearchExceptionHandle which depends on the class initializer for
all the classes that extend ElasticsearchException, but these classes
can not be loaded because ElasticsearchException has not finished its
class initializer. There are tests that can trigger this before
ElasticsearchException has been loaded due to an unlucky ordering of
test execution. This commit addresses this issue by making
ElasticsearchExceptionHandle private, and then exposing methods that
provide the necessary values from ElasticsearchExceptionHandle. Touching
these methods will force the class initializer for
ElasticsearchException to run first.

core/src/main/java/org/elasticsearch/ElasticsearchException.java

@@ -23,6 +23,7 @@ import org.elasticsearch.action.support.replication.ReplicationOperation;
 import org.elasticsearch.cluster.action.shard.ShardStateAction;
 import org.elasticsearch.common.CheckedFunction;
 import org.elasticsearch.common.Nullable;
+import org.elasticsearch.common.collect.Tuple;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.common.io.stream.Writeable;
@@ -712,7 +713,7 @@ public class ElasticsearchException extends RuntimeException implements ToXConte
      * in id order below. If you want to remove an exception leave a tombstone comment and mark the id as null in
      * ExceptionSerializationTests.testIds.ids.
      */
-    enum ElasticsearchExceptionHandle {
+    private enum ElasticsearchExceptionHandle {
         INDEX_SHARD_SNAPSHOT_FAILED_EXCEPTION(org.elasticsearch.index.snapshots.IndexShardSnapshotFailedException.class,
                 org.elasticsearch.index.snapshots.IndexShardSnapshotFailedException::new, 0, UNKNOWN_VERSION_ADDED),
         DFS_PHASE_EXECUTION_EXCEPTION(org.elasticsearch.search.dfs.DfsPhaseExecutionException.class,
@@ -1006,6 +1007,30 @@ public class ElasticsearchException extends RuntimeException implements ToXConte
         }
     }
 
+    /**
+     * Returns an array of all registered handle IDs. These are the IDs for every registered
+     * exception.
+     *
+     * @return an array of all registered handle IDs
+     */
+    static int[] ids() {
+        return Arrays.stream(ElasticsearchExceptionHandle.values()).mapToInt(h -> h.id).toArray();
+    }
+
+    /**
+     * Returns an array of all registered pairs of handle IDs and exception classes. These pairs are
+     * provided for every registered exception.
+     *
+     * @return an array of all registered pairs of handle IDs and exception classes
+     */
+    static Tuple<Integer, Class<? extends ElasticsearchException>>[] classes() {
+        @SuppressWarnings("unchecked")
+        final Tuple<Integer, Class<? extends ElasticsearchException>>[] ts =
+                Arrays.stream(ElasticsearchExceptionHandle.values())
+                        .map(h -> Tuple.tuple(h.id, h.exceptionClass)).toArray(Tuple[]::new);
+        return ts;
+    }
+
     static {
         ID_TO_SUPPLIER = unmodifiableMap(Arrays
                 .stream(ElasticsearchExceptionHandle.values()).collect(Collectors.toMap(e -> e.id, e -> e.constructor)));

core/src/test/java/org/elasticsearch/ExceptionSerializationTests.java

@@ -43,6 +43,7 @@ import org.elasticsearch.common.UUIDs;
 import org.elasticsearch.common.breaker.CircuitBreakingException;
 import org.elasticsearch.common.bytes.BytesArray;
 import org.elasticsearch.common.bytes.BytesReference;
+import org.elasticsearch.common.collect.Tuple;
 import org.elasticsearch.common.io.PathUtils;
 import org.elasticsearch.common.io.stream.BytesStreamOutput;
 import org.elasticsearch.common.io.stream.NotSerializableExceptionWrapper;
@@ -680,15 +681,15 @@ public class ExceptionSerializationTests extends ESTestCase {
     }
 
     public void testThatIdsArePositive() {
-        for (ElasticsearchException.ElasticsearchExceptionHandle handle : ElasticsearchException.ElasticsearchExceptionHandle.values()) {
-            assertThat("negative id", handle.id, greaterThanOrEqualTo(0));
+        for (final int id : ElasticsearchException.ids()) {
+            assertThat("negative id", id, greaterThanOrEqualTo(0));
         }
     }
 
     public void testThatIdsAreUnique() {
-        Set<Integer> ids = new HashSet<>();
-        for (ElasticsearchException.ElasticsearchExceptionHandle handle : ElasticsearchException.ElasticsearchExceptionHandle.values()) {
-            assertTrue("duplicate id", ids.add(handle.id));
+        final Set<Integer> ids = new HashSet<>();
+        for (final int id: ElasticsearchException.ids()) {
+            assertTrue("duplicate id", ids.add(id));
         }
     }
 
@@ -848,8 +849,9 @@ public class ExceptionSerializationTests extends ESTestCase {
             }
         }
 
-        for (ElasticsearchException.ElasticsearchExceptionHandle handle : ElasticsearchException.ElasticsearchExceptionHandle.values()) {
-            assertEquals((int) reverse.get(handle.exceptionClass), handle.id);
+        for (final Tuple<Integer, Class<? extends ElasticsearchException>> tuple : ElasticsearchException.classes()) {
+            assertNotNull(tuple.v1());
+            assertEquals((int) reverse.get(tuple.v2()), (int)tuple.v1());
         }
 
         for (Map.Entry<Integer, Class<? extends ElasticsearchException>> entry : ids.entrySet()) {