Introduce XContentParser#namedObject (#22003)

Introduces `XContentParser#namedObject which works a little like
`StreamInput#readNamedWriteable`: on startup components register
parsers under names and a superclass. At runtime we look up the
parser and call it to parse the object.

Right now the parsers take a context object they use to help with
the parsing but I hope to be able to eliminate the need for this
context as most what it is used for at this point is to move
around parser registries which should be replaced by this method
eventually. I make no effort to do so in this PR because it is
big enough already. This is meant to the a start down a road that
allows us to remove classes like `QueryParseContext`,
`AggregatorParsers`, `IndicesQueriesRegistry`, and
`ParseFieldRegistry`.

The goal here is to reduce the amount of plumbing required to
allow parsing pluggable things. With this you don't have to pass
registries all over the place. Instead you must pass a super
registry to fewer places and use it to wrap the reader. This is
the same tradeoff that we use for NamedWriteable and it allows
much, much simpler binary serialization. We think we want that
same thing for xcontent serialization.

The only parsing actually converted to this method is parsing
`ScoreFunctions` inside of `FunctionScoreQuery`. I chose this
because it is relatively self contained.

2 files changed, 8 insertions, 8 deletions

diff --git a/core/src/test/java/org/elasticsearch/action/support/replication/ReplicationResponseTests.java b/core/src/test/java/org/elasticsearch/action/support/replication/ReplicationResponseTests.java
index 966bee8f85..ca8f0a4c6b 100644
--- a/core/src/test/java/org/elasticsearch/action/support/replication/ReplicationResponseTests.java
+++ b/core/src/test/java/org/elasticsearch/action/support/replication/ReplicationResponseTests.java
@@ -122,7 +122,7 @@ public class ReplicationResponseTests extends ESTestCase {
         final BytesReference shardInfoBytes = XContentHelper.toXContent(shardInfo, xContentType, true);
 
         // Expected JSON is {"_shards":{"total":5,"successful":3,"failed":0}}
-        try (XContentParser parser = xContentType.xContent().createParser(shardInfoBytes)) {
+        try (XContentParser parser = createParser(xContentType.xContent(), shardInfoBytes)) {
             assertEquals(XContentParser.Token.START_OBJECT, parser.nextToken());
             assertEquals(XContentParser.Token.FIELD_NAME, parser.nextToken());
             assertEquals("_shards", parser.currentName());
@@ -152,7 +152,7 @@ public class ReplicationResponseTests extends ESTestCase {
         final BytesReference shardInfoBytes = XContentHelper.toXContent(shardInfo, xContentType, true);
 
         ReplicationResponse.ShardInfo parsedShardInfo;
-        try (XContentParser parser = xContentType.xContent().createParser(shardInfoBytes)) {
+        try (XContentParser parser = createParser(xContentType.xContent(), shardInfoBytes)) {
             // Move to the start object that was manually added when building the object
             assertEquals(XContentParser.Token.START_OBJECT, parser.nextToken());
             parsedShardInfo = ReplicationResponse.ShardInfo.fromXContent(parser);
@@ -172,7 +172,7 @@ public class ReplicationResponseTests extends ESTestCase {
         final ReplicationResponse.ShardInfo shardInfo = randomShardInfo();
         final BytesReference shardInfoBytes = XContentHelper.toXContent(shardInfo, xContentType, true);
 
-        try (XContentParser parser = xContentType.xContent().createParser(shardInfoBytes)) {
+        try (XContentParser parser = createParser(xContentType.xContent(), shardInfoBytes)) {
             assertEquals(XContentParser.Token.START_OBJECT, parser.nextToken());
             assertEquals(XContentParser.Token.FIELD_NAME, parser.nextToken());
             assertEquals("_shards", parser.currentName());
@@ -214,7 +214,7 @@ public class ReplicationResponseTests extends ESTestCase {
         final BytesReference shardInfoBytes = XContentHelper.toXContent(shardInfo, xContentType, true);
 
         ReplicationResponse.ShardInfo parsedShardInfo;
-        try (XContentParser parser = xContentType.xContent().createParser(shardInfoBytes)) {
+        try (XContentParser parser = createParser(xContentType.xContent(), shardInfoBytes)) {
             // Move to the start object that was manually added when building the object
             assertEquals(XContentParser.Token.START_OBJECT, parser.nextToken());
             parsedShardInfo = ReplicationResponse.ShardInfo.fromXContent(parser);
@@ -254,7 +254,7 @@ public class ReplicationResponseTests extends ESTestCase {
         final ReplicationResponse.ShardInfo.Failure shardInfoFailure = randomFailure();
         final BytesReference shardInfoBytes = XContentHelper.toXContent(shardInfoFailure, xContentType, false);
 
-        try (XContentParser parser = xContentType.xContent().createParser(shardInfoBytes)) {
+        try (XContentParser parser = createParser(xContentType.xContent(), shardInfoBytes)) {
             assertFailure(parser, shardInfoFailure);
         }
     }
@@ -266,7 +266,7 @@ public class ReplicationResponseTests extends ESTestCase {
         final BytesReference shardInfoBytes = XContentHelper.toXContent(shardInfoFailure, xContentType, false);
 
         ReplicationResponse.ShardInfo.Failure parsedFailure;
-        try (XContentParser parser = xContentType.xContent().createParser(shardInfoBytes)) {
+        try (XContentParser parser = createParser(xContentType.xContent(), shardInfoBytes)) {
             // Move to the first start object
             assertEquals(XContentParser.Token.START_OBJECT, parser.nextToken());
             parsedFailure = ReplicationResponse.ShardInfo.Failure.fromXContent(parser);
diff --git a/core/src/test/java/org/elasticsearch/action/support/replication/TransportReplicationActionTests.java b/core/src/test/java/org/elasticsearch/action/support/replication/TransportReplicationActionTests.java
index 7644c88df3..d2c56f45b3 100644
--- a/core/src/test/java/org/elasticsearch/action/support/replication/TransportReplicationActionTests.java
+++ b/core/src/test/java/org/elasticsearch/action/support/replication/TransportReplicationActionTests.java
@@ -360,8 +360,8 @@ public class TransportReplicationActionTests extends ESTestCase {
     public void testClosedIndexOnReroute() throws InterruptedException {
         final String index = "test";
         // no replicas in oder to skip the replication part
-        setState(clusterService,
-            new ClusterStateChanges().closeIndices(state(index, true, ShardRoutingState.UNASSIGNED), new CloseIndexRequest(index)));
+        setState(clusterService, new ClusterStateChanges(xContentRegistry()).closeIndices(state(index, true, ShardRoutingState.UNASSIGNED),
+                new CloseIndexRequest(index)));
         logger.debug("--> using initial state:\n{}", clusterService.state());
         Request request = new Request(new ShardId("test", "_na_", 0)).timeout("1ms");
         PlainActionFuture<Response> listener = new PlainActionFuture<>();