Field mapping API unexpectedly returns 404 response

[tylersmalley]

Elasticsearch version: master/8.0

Description of the problem including expected versus actual behavior: Field mapping API returns an empty response when the mapping contains a property not indexed and requested with include_defaults=true

Steps to reproduce:

Building upon the example provided in the field mapping API docs.

1. Create an index containing a property with index: false

curl -X PUT "localhost:9200/publications?pretty" -H 'Content-Type: application/json' -d'
{
    "mappings": {
        "properties": {
            "id": { "type": "text" },
            "title":  { "type": "text"},
            "abstract": { "type": "text", "index": false },
            "author": {
                "properties": {
                    "id": { "type": "text" },
                    "name": { "type": "text" }
                }
            }
        }
    }
}
'

2. Request all fields with include_defaults=true

curl -X GET "localhost:9200/_mapping/field/*?index=publications&allow_no_indices=false&include_defaults=true"

3. Observe 404 response

curl -i -X GET "localhost:9200/_mapping/field/*?index=publications&allow_no_indices=false&include_defaults=true"
HTTP/1.1 404 Not Found
content-type: application/json; charset=UTF-8
content-length: 2

{}%

[tylersmalley]

This failure was caught by our nightly checks against Elasticsearch, so we will need to resolve this or understand how to move forward in order to unblock that process. Thanks!

[elasticmachine]

Pinging @elastic/es-search (:Search/Mapping)

[jtibshirani]

This could be due to the MappedFieldType refactor (#57666), since there were changes to the include_defaults behavior. Tagging @romseygeek so he could take a look.