Thanks @n9! That's definitely a bug.

I'm not exactly sure what I was thinking when I wrote this line. I think I must have only been thinking about term queries that don't contain wildcard characters.

I think it might be worthwhile to refactor WildcardFieldType to use a nice unified code path built around the regexp use-case.

Specifically:

1. A term query can be turned into a simple regular expression (i.e. any syntax is escaped).
2. A wildcard query can be converted to a regexp by replacing (unescaped) ? with . and (unescaped) * with .*. (Any other regexp characters would need to be escaped.)
3. A prefix query can be converted to a regexp by escaping any syntax and appending .*.
4. A terms query is just a bunch of escaped term expressions joined with the alternative (|) operator.

Then we can make sure that one code path works well with case-insensitive flags and appropriate approximation and automaton matching. As a bonus, that solution would address this issue and #16755.

Are you able to work on a fix? If not, would you be able to contribute a failing test case to https://github.com/opensearch-project/OpenSearch/blob/aaa92aeeb75a745ee7b058cc4b30b734e861cfc4/rest-api-spec/src/main/resources/rest-api-spec/test/search/270_wildcard_fieldtype_queries.yml?

@msfroh
I'm wondering whether you are already working on this problem. If not, I'm willing to try : )

Hey @HUSTERGS ! I wanted to give @n9 the chance to take it, then I was planning to reach out to you to see if you are interested.

I'll go ahead and assign it to you. Thanks a lot!

Hi @msfroh @HUSTERGS, sorry for the delay, I am currently out of time.