Simulate mapping changes

[flash1293]

Description

The ingest simulate API returns the resulting doc after all ingest pipelines are applied and eventual mapping errors.

However, the resulting mappings are not returned to the user. As there are a bunch of features that can influence how mappings turn out (dynamic templates, component templates with priorities, index templates with priorities), it's not trivial for a user to infer this manual and it would be great if the existing simulate ingest API could also return the resulting mapping of the eventual target index after a set of documents would have been indexed.

For example, when I'm sending a doc like

{
  "client.ip": "1.2.3.4.5"
}

it's not trivial to tell whether client.ip will be mapped as a keyword or as an ip, but it's a very important piece of information.

[elasticsearchmachine]

Pinging @elastic/es-data-management (Team:Data Management)

[masseyke]

I'm guessing that the thing you're simulating ingesting into is usually a data stream, right? Have you looked into the effective_mappings section of the /_data_stream/{name}/_mappings API as a workaround? Since the simulate ingest API gives you the index name, and in your case the index name is really a data stream name, I think it would just take another request to get the effective mappings for that data stream.
Edit: That's only a useful workaround if you're not simulating mapping changes, which you probably are. So you can probably disregard my comment.