Fix type annotation of source parameter.

[JannKleen]

This might be completely wrong, but I think the type hinting of the source parameter for Elasticsearch().search() should be Sequence[str] and not Mapping[str, Any] (s. https://www.elastic.co/guide/en/elasticsearch/reference/current/search-fields.html#source-filtering)
Also fields should be accepting str as well as Mapping[str, Any]

[pquentin]

Hello, and thank you! However this code is generated from https://github.com/elastic/elasticsearch-specification/blob/main/specification/_global/search/SearchRequest.ts which is the place to fix if the type hint is wrong.

More specifically, https://github.com/elastic/elasticsearch-specification/blob/main/specification/_types/query_dsl/abstractions.ts is the definition of one field, which explains why it's a mapping. (The Python client only has types for the first level of objects.)

You are right that Elasticsearch accepts single strings too (https://www.elastic.co/guide/en/elasticsearch/reference/current/search-fields.html#search-fields-request shows it clearly) which suggests the specification repo could be fixed.

If you are unable to open an issue or pull request in that repository, I can look at this in more detail at the end of next week.

[pquentin]

Closing in favor of elastic/elasticsearch-specification#2317. Thanks!