Transform specs are ignored if dimension auto detection is used

[vogievetsky]

The column auto detecting feature does not find the new columns created by transforms.

Affected Version

All versions of Druid so far (up to 0.15.0)

Description

Say you have data:

{"a":"hello","b":"world"}
{"a":"where","c":"to go"}

In a file that lives at: /Users/vadim/Downloads/test-data.json

And you ingest it with:

{
  "dataSchema": {
    "dataSource": "Downloads",
    "parser": {
      "type": "string",
      "parseSpec": {
        "format": "json",
        "timestampSpec": {
          "column": "!!!_no_such_column_!!!",
          "missingValue": "2010-01-01T00:00:00Z"
        },
        "dimensionsSpec": {}
      }
    },
    "metricsSpec": [
      {
        "name": "count",
        "type": "count"
      }
    ],
    "granularitySpec": {
      "type": "uniform",
      "segmentGranularity": "DAY",
      "queryGranularity": "HOUR",
      "rollup": true,
      "intervals": null
    },
    "transformSpec": {
      "filter": null,
      "transforms": [
        {
          "type": "expression",
          "name": "a_prime",
          "expression": "concat(\"a\",'_prime')"
        }
      ]
    }
  },
  "ioConfig": {
    "type": "index_parallel",
    "firehose": {
      "type": "local",
      "baseDir": "/Users/vadim/Downloads",
      "filter": "test-data.json"
    },
    "appendToExisting": false
  },
  "tuningConfig": {
    "type": "index_parallel",
    "maxRowsPerSegment": null,
    "maxRowsInMemory": 1000000,
    "maxBytesInMemory": 0,
    "maxTotalRows": null,
    "numShards": null,
    "indexSpec": {
      "bitmap": {
        "type": "concise"
      },
      "dimensionCompression": "lz4",
      "metricCompression": "lz4",
      "longEncoding": "longs"
    },
    "maxPendingPersists": 0,
    "forceGuaranteedRollup": false,
    "reportParseExceptions": false,
    "pushTimeout": 0,
    "segmentWriteOutMediumFactory": null,
    "maxNumSubTasks": 1,
    "maxRetry": 3,
    "taskStatusCheckPeriodMs": 1000,
    "chatHandlerTimeout": "PT10S",
    "chatHandlerNumRetries": 5,
    "logParseExceptions": false,
    "maxParseExceptions": 2147483647,
    "maxSavedParseExceptions": 0,
    "partitionDimensions": [],
    "buildV9Directly": true
  },
  "type": "index_parallel"
}

Notice how I am trying to create an a_prime column with a transform spec.

The job will work but when you query the data:

You see that there is no a_prime column.

I would be great (and would make a ton more sense) if the transforms added themselves to the column list coming from the file.