Index prefixes on fields

We have a setup where some fields are analyzed in multiple ways: with the standard analyzer and a custom analyzer my_analyzer that preserves punctuation and capitalisation. We want to be able to perform prefix search on both fields. As such we want to apply index_prefixes to the relevant fields. We have tried the following mapping

{
  "mapping": {
    "properties": {
      "field1": {
        "type": "text",
        "index_prefixes": {},
        "fields": {
          "exact": {
            "type": "text"
            "analyzer": "my_analyzer",
            "index_prefixes": {}
          }
        }
      },
      "field2": {
        "type": "text",
        "index_prefixes": {},
        "fields": {
          "exact": {
            "type": "text"
            "analyzer": "my_analyzer",
            "index_prefixes": {}
          }
        }
      }
    }
  }
}

But creating an index with this mapping produces:

{
    "error": {
        "root_cause": [
            {
                "type": "illegal_argument_exception",
                "reason": "Field [exact._index_prefix] is defined twice."
            }
        ],
        "type": "illegal_argument_exception",
        "reason": "Field [exact._index_prefix] is defined twice."
    },
    "status": 400
}

If we remove the index_prefixes from the exact fields, the index creation succeeds. In other words, change the mapping to:

{
  "mapping": {
    "properties": {
      "field1": {
        "type": "text",
        "index_prefixes": {},
        "fields": {
          "exact": {
            "type": "text"
            "analyzer": "my_analyzer"
          }
        }
      },
      "field2": {
        "type": "text",
        "index_prefixes": {},
        "fields": {
          "exact": {
            "type": "text"
            "analyzer": "my_analyzer"
          }
        }
      }
    }
  }
}

But are prefixes indexed on field1.exact and field2.exact if index_prefixes is only present on the field1 and field2? If not, what is the correct way to do this? The documentation does not mention anything about fields.

Hi, this is a known bug that was fixed in the 7.2.1 release: https://github.com/elastic/elasticsearch/pull/43862

-Alan