XContent: Trying to use a writer with date formats results in serialization issues

[spinscale]

fails under 6.3.1/6.3.0.

PUT foo/bar/1?refresh=true
{
  "key" : 123
}

GET foo/_search
{
  "script_fields": {
    "custom": {
      "script": {
        "source" : "return Instant.ofEpochMilli(123)"
      }
    }
  }
}

results in

# GET foo/_search
{
  "error": {
    "root_cause": [
      {
        "type": "illegal_argument_exception",
        "reason": "cannot write xcontent for unknown value of type class java.time.Instant"
      }
    ],
    "type": "illegal_argument_exception",
    "reason": "cannot write xcontent for unknown value of type class java.time.Instant"
  },
  "status": 400
}

exact stack trace

java.lang.IllegalArgumentException: cannot write xcontent for unknown value of type class java.time.Instant
	at org.elasticsearch.common.xcontent.XContentBuilder.unknownValue(XContentBuilder.java:755)
	at org.elasticsearch.common.xcontent.XContentBuilder.value(XContentBuilder.java:726)
	at org.elasticsearch.common.document.DocumentField.toXContent(DocumentField.java:131)
	at org.elasticsearch.search.SearchHit.toInnerXContent(SearchHit.java:456)
	at org.elasticsearch.search.SearchHit.toXContent(SearchHit.java:398)
	at org.elasticsearch.search.SearchHits.toXContent(SearchHits.java:117)
	at org.elasticsearch.action.search.SearchResponseSections.toXContent(SearchResponseSections.java:106)
	at org.elasticsearch.action.search.SearchResponse.innerToXContent(SearchResponse.java:241)
	at org.elasticsearch.action.search.SearchResponse.toXContent(SearchResponse.java:221)
	at org.elasticsearch.rest.action.RestStatusToXContentListener.buildResponse(RestStatusToXContentListener.java:57)
	at org.elasticsearch.rest.action.RestStatusToXContentListener.buildResponse(RestStatusToXContentListener.java:33)
	at org.elasticsearch.rest.action.RestToXContentListener.buildResponse(RestToXContentListener.java:42)
	at org.elasticsearch.rest.action.RestToXContentListener.buildResponse(RestToXContentListener.java:34)
	at org.elasticsearch.rest.action.RestResponseListener.processResponse(RestResponseListener.java:37)
	at org.elasticsearch.rest.action.RestActionListener.onResponse(RestActionListener.java:47)
	at org.elasticsearch.action.support.TransportAction$1.onResponse(TransportAction.java:85)
	at org.elasticsearch.action.support.TransportAction$1.onResponse(TransportAction.java:81)
	at org.elasticsearch.action.search.AbstractSearchAsyncAction.onResponse(AbstractSearchAsyncAction.java:308)
	at org.elasticsearch.action.search.AbstractSearchAsyncAction.onResponse(AbstractSearchAsyncAction.java:48)
	at org.elasticsearch.action.search.FetchSearchPhase$3.run(FetchSearchPhase.java:212)
	at org.elasticsearch.action.search.AbstractSearchAsyncAction.executePhase(AbstractSearchAsyncAction.java:155)
	at org.elasticsearch.action.search.AbstractSearchAsyncAction.executeNextPhase(AbstractSearchAsyncAction.java:148)
	at org.elasticsearch.action.search.ExpandSearchPhase.run(ExpandSearchPhase.java:118)
	at org.elasticsearch.action.search.AbstractSearchAsyncAction.executePhase(AbstractSearchAsyncAction.java:155)
	at org.elasticsearch.action.search.AbstractSearchAsyncAction.executeNextPhase(AbstractSearchAsyncAction.java:148)
	at org.elasticsearch.action.search.FetchSearchPhase.moveToNextPhase(FetchSearchPhase.java:205)
	at org.elasticsearch.action.search.FetchSearchPhase.lambda$innerRun$2(FetchSearchPhase.java:104)
	at org.elasticsearch.action.search.CountedCollector.countDown(CountedCollector.java:53)
	at org.elasticsearch.action.search.CountedCollector.onResult(CountedCollector.java:64)
	at org.elasticsearch.action.search.FetchSearchPhase$2.innerOnResponse(FetchSearchPhase.java:165)
	at org.elasticsearch.action.search.FetchSearchPhase$2.innerOnResponse(FetchSearchPhase.java:162)
	at org.elasticsearch.action.search.SearchActionListener.onResponse(SearchActionListener.java:45)
	at org.elasticsearch.action.search.SearchActionListener.onResponse(SearchActionListener.java:29)
	at org.elasticsearch.action.ActionListenerResponseHandler.handleResponse(ActionListenerResponseHandler.java:46)
	at org.elasticsearch.action.search.SearchTransportService$ConnectionCountingHandler.handleResponse(SearchTransportService.java:518)
	at org.elasticsearch.transport.TransportService$ContextRestoreResponseHandler.handleResponse(TransportService.java:1096)
	at org.elasticsearch.transport.TransportService$DirectResponseChannel.processResponse(TransportService.java:1165)
	at org.elasticsearch.transport.TransportService$DirectResponseChannel.sendResponse(TransportService.java:1155)
	at org.elasticsearch.transport.TransportService$DirectResponseChannel.sendResponse(TransportService.java:1144)
	at org.elasticsearch.transport.TaskTransportChannel.sendResponse(TaskTransportChannel.java:54)
	at org.elasticsearch.action.search.SearchTransportService$11.messageReceived(SearchTransportService.java:441)
	at org.elasticsearch.action.search.SearchTransportService$11.messageReceived(SearchTransportService.java:437)
	at org.elasticsearch.xpack.security.transport.SecurityServerTransportInterceptor$ProfileSecuredRequestHandler$1.doRun(SecurityServerTransportInterceptor.java:259)
	at org.elasticsearch.common.util.concurrent.AbstractRunnable.run(AbstractRunnable.java:37)
	at org.elasticsearch.xpack.security.transport.SecurityServerTransportInterceptor$ProfileSecuredRequestHandler.messageReceived(SecurityServerTransportInterceptor.java:317)
	at org.elasticsearch.transport.RequestHandlerRegistry.processMessageReceived(RequestHandlerRegistry.java:66)
	at org.elasticsearch.transport.TransportService$7.doRun(TransportService.java:664)
	at org.elasticsearch.common.util.concurrent.ThreadContext$ContextPreservingAbstractRunnable.doRun(ThreadContext.java:725)
	at org.elasticsearch.common.util.concurrent.AbstractRunnable.run(AbstractRunnable.java:37)
	at org.elasticsearch.common.util.concurrent.TimedRunnable.doRun(TimedRunnable.java:41)
	at org.elasticsearch.common.util.concurrent.AbstractRunnable.run(AbstractRunnable.java:37)
	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1135)
	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:635)
	at java.base/java.lang.Thread.run(Thread.java:844)
"

[elasticmachine]

Pinging @elastic/es-core-infra

[spinscale]

the issue for this is, that the date transformers (where there is one for Instant) only are checked if you use writeTimeField(), however this one is just a regular writer, thus this fails, because nothing is registered for Instant.

This used to work under 6.2 and fails under 6.3

[spinscale]

Note that this change affects ML watches created via the Kibana UI, see elastic/kibana#18376

[shahid21st]

Similar thing happens in Java API, if I build a query with RangeQueryBuilder with to/from parameters using LocalDate and then do a toString() to get the translated query. This happens as XContentElasticsearchExtension has no transformers for LocalDate and also XContentBuilder has no writer for LocalDate.
For LocalDate or related classes it might be possible to check whether the object is an implementation of Temporal interface and invoke toString(). But looking at #32395 , it seems, it would need a proper solution to address all of these.