Returning ignored fields in the simulate ingest API

[masseyke]

As described in #116497, A new ignored_fields array is returned if ingest would ignore any fields in the input. For example:

curl -X POST "localhost:9200/_ingest/_simulate?pretty" -H 'Content-Type: application/json' -d'
{
  "docs": [
    {        
      "_index": "simulate-test",
      "_id": "y9Es_JIBiw6_GgN-U0qy",
      "_score": 1,
      "_source": {
        "abc": "sfdsfsfdsfsfdsfsfdsfsfdsfsfdsf"
      }    
    }      
  ],
  "index_template_substitutions": {
    "ind_temp": {
      "index_patterns": ["simulate-test"],
      "composed_of": ["simulate-test"]
    }    
  },
  "component_template_substitutions": {
    "simulate-test": {
      "template": {
        "mappings": {
          "dynamic": false,
          "properties": {
            "abc": {
              "type": "keyword",
              "ignore_above": 1
            }
          }  
        }    
      }    
    }      
  }
}
'
{
  "docs" : [
    {
      "doc" : {
        "_id" : "y9Es_JIBiw6_GgN-U0qy",
        "_index" : "simulate-test",
        "_version" : -3,
        "_source" : {
          "abc" : "sfdsfsfdsfsfdsfsfdsfsfdsfsfdsf"
        },
        "executed_pipelines" : [ ],
        "ignored_fields" : [
          {
            "field": "abc"
          }
        ]
      }
    }
  ]
}

[elasticsearchmachine]

Hi @masseyke, I've created a changelog YAML for you.

[elasticsearchmachine]

Pinging @elastic/es-data-management (Team:Data Management)

[dakrone]

LGTM, thanks Keith!

[dakrone]

Hah, nice catch :)

[dakrone]

We could probably just do return List.of(); here and avoid having to create the ignoredFields local field? It's not a big deal either way though.

[masseyke]

I kind of prefer having a single return statement rather than 3 -- it makes debugging easier for me.

[dakrone]

I'm okay either way :)

[dakrone]

Should we add an assert luceneDocuments().size() == 1 somewhere here to ensure that we fail if in the future a single index request results in more than one doc? (We'd silently ignored the response if we didn't)

[masseyke]

Sounds good.

[elasticsearchmachine]

💚 Backport successful

Status	Branch	Result
✅	8.x