To double-check I understand -- we could already remove the mentions to _doc in mapping definitions, but we'll postpone that for another PR? This approach makes sense to me, as it helps keep the current PR focused.

That's correct - there's also still a bit of inconsistency as to when things need to be wrapped and when not, which this PR moves us one more step towards resolving.

👍

For consistency with the changes in CreateIndexRequestBuilder, it would be great if we also removed the type parameter from public CreateIndexRequest mapping(String type, Map<String, ?> source), and converted as many callers as possible to use the new signature. Here's a suggestion for how to do it:

    public CreateIndexRequest mapping(Map<String, ?> source) {
        return mapping(MapperService.SINGLE_MAPPING_NAME, source);
    }

    private CreateIndexRequest mapping(String type, Map<String, ?> source) {
        // wrap it in a type map if its not
        if (source.size() != 1 || !source.containsKey(type)) {
            source = Map.of(MapperService.SINGLE_MAPPING_NAME, source);
        }
        ...
    }

The private method is still needed to support CreateIndexRequest#source.

++

For context, what's the plan to remove these remaining methods that accept Object... source?

My current plan is to have a new method, mappingFromSimplifiedDef(Objects... source), and remove the existing method, to make sure that we get compilation failures rather than silently treating the type parameter as part of the source.