Elasticsearch should raise a mapper exception when reserved "mapping fields" are used inside "properties"

[konradkonrad]

Unfortunately it is possible to use "top-level"/meta mapping properties, such as _source, _all, ... inside the "properties": {} portion of a mapping, without complaints. This allows for user errors that are easily missed.

Using the following mapping

{
  "t1": {
    "_source": {"enabled": false}, 
    "properties": {
      "_all": {"enabled": false},
      "field1": {"type": "string"},
      "field2": {"type": "long"},
      "_underscore1": {"type": "string"},
      "_underscore2": {"enabled": true}
    }
  }
}

will lead to:

{
  "mytest" : {
    "mappings" : {
      "t1" : {
        "_source" : {
          "enabled" : false
        },
        "properties" : {
          "_underscore1" : {
            "type" : "string"
          },
          "_underscore2" : {
            "type" : "object"
          },
          "field1" : {
            "type" : "string"
          },
          "field2" : {
            "type" : "long"
          }
        }
      }
    }
  }
}

Note, how the _all-"Field-Mapping" is just silently ignored.

Please see https://gist.github.com/konradkonrad/16220520eb9bacc1f6e6 for a complete reproduction.

[clintongormley]

Relates to #9059

[konradkonrad]

@clintongormley thx for labelling this!

While I totally agree on the relation to #9059, I believe this one should/could be addressed ahead of time, since atm there exists a set of should-be-reserved words: Mapping » Fields*)

As the _all example seems to show, there is also some validation already in place. I cannot tell how many users use ambigous field names such as _timestamp, and I understand the BC concerns of #9059 -- however from my POV I'd rather have users become aware of their misconfigured mappings, then serve the BC needs of mappings using questionable ambigous names.

*) SN: btw. pretty unfortunate naming in the docs imho, what about one of these?

• Mapping » DocType Configuration
• Mapping » DocType Settings
• Mapping » Mapping Configuration
• Mapping » Top-Level Fields

[jpountz]

Fixed via #15243