Set Processor will change field type in _source field when use Mustache

[kin122]

Elasticsearch Version

all

Installed Plugins

No response

Java Version

bundled

OS Version

linux 4.18.0-348.7.1.el8_5.x86_64

Problem Description

we found this problem, when Mustache is used to refer to a field content, the Set Processor changes the field type in the _source field

Steps to Reproduce

# test index
PUT /test
{
  "mappings": {
    "properties": {
      "status": {
        "type": "integer"
      }
    }
  }
}
# test data
POST /test/_bulk
{"index":{}}
{"status":404}
{"index":{}}
{"status":500}

GET test/_search
# status's type is integer in _source
    "hits": [
      {
        "_index": "test",
        "_type": "_doc",
        "_id": "2ry5NpUBLvnTvXTp1F5z",
        "_score": 1,
        "_source": {
          "status": 404 
        }
      },
      {
        "_index": "test",
        "_type": "_doc",
        "_id": "27y5NpUBLvnTvXTp1F5z",
        "_score": 1,
        "_source": {
          "status": 500
        }
      }
    ]

# add subfield
PUT test/_mapping
{
  "properties": {
    "status": {
      "type": "integer",
      "fields": {
        "keyword": {
          "type": "keyword"
        }
      }
    }
  }
}

# create set processor, use Mustache
PUT _ingest/pipeline/copy_status_to_keyword
{
  "description": "resets the value of status and subfields",
  "processors": [
    {
      "set": {
        "field": "status",
        "value": "{{{status}}}"
      }
    }
  ]
}

# update data
POST test/_update_by_query?pipeline=copy_status_to_keyword
{
  "query": {
    "bool": {
      "must_not": {
        "exists": {
          "field": "status.keyword"
        }
      },
      "must": {
        "exists": {
          "field": "status"
        }
      }
    }
  }
}


GET test/_search
{
  "query": {
    "exists": {
      "field": "status.keyword"
    }
  }
}

# results
   "hits": [
      {
        "_index": "test_set",
        "_type": "_doc",
        "_id": "G7zHNpUBLvnTvXTpVIC4",
        "_score": 1,
        "_source": {
          "status": "404" # status's type is changed ,being string
        }
      },
      {
        "_index": "test_set",
        "_type": "_doc",
        "_id": "HLzHNpUBLvnTvXTpVIC4",
        "_score": 1,
        "_source": {
          "status": "500"
        }
      }
    ]

Logs (if relevant)

No response

[elasticsearchmachine]

Pinging @elastic/es-core-infra (Team:Core/Infra)