[BUG] Transform API should throw exception for unsupported aggregation type

[Angie-Zhang]

What is the bug?
When creating transform jobs, even if the request format contains unsupported aggregation types, the transform API still returns 201 success. After the transform job created, the job has Error Status.

How can one reproduce the bug?
In Dev Tools set a request to create a transform job:

PUT _plugins/_transform/bucket_script_test
{
  "transform": {
    "enabled": true,
    "continuous": true,
    "schedule": {
      "interval": {
        "period": 1,
        "unit": "Minutes"
      }
    },
    "description": "Sample transform job",
    "source_index": "transform_test_source",
    "target_index": "transform_test_target",
    "data_selection_query": {
      "match_all": {}
    },
    "page_size": 1,
    "groups": [
      {
        "terms": {
          "source_field": "price",
          "target_field": "original_price"
        }
      },
      {
        "terms": {
          "source_field": "discount",
          "target_field": "discount"
        }
      }
    ],
    "aggregations": {
       "final_price": {
        "bucket_script": {
            "buckets_path": {
                "p": "price",
                "d": "discount"
            },
            "script": "params.p * (1 - params.d)"
        }
    }
    }
  }
}

It returns 201 success.

In Index Management - Transform Jobs, this job can be seen with Status: Error: Failed to search data in source indices.

What is the expected behavior?
IN OS 2.5 or earlier version, transform does not support bucket_script in aggregation. It should throw exception to reflect this eror.

What is your host/environment?

• OS: AWS Managed Service
• Version: OS 1.3 & OS 2.3

[n-dohrmann]

Could I be assigned this issue? thanks!