[Flex]: flex query not selecting the index with doc id regex as type identifier

Build : 7.1.0-2304

• Load travel -sample
• create index like below:

  {

  "type": "fulltext-index",

  "name": "travel-index",

  "uuid": "1a448bf79b6c5ff2",

  "sourceType": "gocbcore",

  "sourceName": "travel-sample",

  "sourceUUID": "456633d80afdabb63fc7295fefed53af",

  "planParams": {

  "maxPartitionsPerPIndex": 1024,

  "indexPartitions": 1

  },

  "params": {

  "doc_config": {

  "docid_prefix_delim": "",

  "docid_regexp": "([^_]*)",

  "mode": "docid_regexp",

  "type_field": "type"

  },

  "mapping": {

  "analysis": {},

  "default_analyzer": "keyword",

  "default_datetime_parser": "dateTimeOptional",

  "default_field": "_all",

  "default_mapping": {

  "dynamic": false,

  "enabled": false

  },

  "default_type": "_default",

  "docvalues_dynamic": true,

  "index_dynamic": true,

  "store_dynamic": false,

  "type_field": "_type",

  "types": {

  "airport": {

  "dynamic": true,

  "enabled": true

  }

  }

  },

  "store": {

  "indexType": "scorch",

  "mossStoreOptions": {},

  "segmentVersion": 15

  }

  },

  "sourceParams": {}

  }

• Below flex query returns "No index available"

  explain select meta().id from `travel-sample` USE INDEX(USING FTS) where meta().`id` like "%airport%" and city = "Delta"

  Note: search query works fine.