Both Kibana and SQL have logic on top of the _field_caps API to detect when a conflict is harmful versus when it's not. Part of how it works is by grouping field types into families of fields: conflicts are fine as long as the types across indices are all of the same family.

Should we move this logic to _field_caps instead?

Here is an example of how we could collapse fields:

• number: long, integer, double, float, scaled_float, ...
• date: date, date_nanos
• keyword: keyword, constant_keyword, wildcard
• text: text
• geo: geo_point, geo_shape

Most other fields would be their own family as they don't share properties with other fields, e.g. boolean or flattened.

So for instance, the below response today is considered a conflict:

{
    "indices": ["index1", "index2", "index3", "index4", "index5"],
    "fields": {
        "rating": { 
            "double": {
                "searchable": true,
                "aggregatable": true,
                "indices": ["index1", "index2"]
            },
            "float": {
                "searchable": true,
                "aggregatable": true,
                "indices": ["index3", "index4"],
            }
        }
    }
}

While it wouldn't be one if we collapsed double and float into a number "family".