Option for excluding fields in "all_fields" query mode

[mr-mos]

In ES 6.0 the indexed "_all" field will be removed and Elastic is promoting the "all_fields" query (default_field=*) that does the same (at query- and not indexed time).

There should be a feature for restricting fields in the all_fields search.
A multi_match or other queries would expect, that clients know which fields are available and should be searched by default. In many cases this is a configuration on the index and shouldn't be known by the client.

It would be nice to have a configuration option similar to the " include_in_all: false" used in the deprecated indexd based _all-field.

This topic was discussed with @dakrone in the the issue #25105 and in the thread https://discuss.elastic.co/t/option-for-excluding-fields-in-all-fields-mode-query-for-es-6-0/93218

[jimczi]

Discussed in Fix it Friday and we agreed that we should also accept an array for the index.query.default_field index setting. It would then be possible to define the default search fields associated with an index. The rules to expand the field names would be the same as if provided as fields in a query_string query.

[mr-mos]

Thanks. Any planning when it will be integrated into ES. beta-2 ?

[jimczi]

Still some blockers on the simple_query_string side but I plan to work on this as soon as #26145 is resolved.