Elasticsearch Version

7.16.3

Installed Plugins

No response

Java Version

bundled

OS Version

Windows 10

Problem Description

I'm looking into a report of a bug raised against the .NET client for use of search templates. The root cause seems to be that while the REST API spec and docs mention that "explain" can be included on the query string, doing so doesn't result in an explanation being returned. Only if it's included in the body is the explanation returned. This appears to be a bug with the parsing of search template rest requests as the explain parameter is not retrieved.

Steps to Reproduce

Make a request with "explain=true" on the query string:

GET test/_search/template?explain=true
{
 "id": "my-search-template",
 "params": {
    "query_string": "hello world",
    "from": 0,
    "size": 10
  }
}

Expected result:
The explanation is included in the results.

Actual:
The explanation is not included.

Logs (if relevant)

No response