Raw mapping merge fix for properties field

[eyalkoren]

Fixes #108866

[elasticsearchmachine]

Pinging @elastic/es-search (Team:Search)

[elasticsearchmachine]

Hi @eyalkoren, I've created a changelog YAML for you.

[felixbarny]

LGTM

[eyalkoren]

cc @chiarch84

[chiarachiarelli]

Thanks a lot for following this. Sorry for not commenting earlier but I do not have access to my pc for some time to test It.

[cbuescher]

I took a deeper look at the custom merge logic in RawFieldMappingMerge and agree that passing on "null" in the recursion when the parent is a "properties" field should not affect any further merging logic down the line.
LGTM for that reason.

[eyalkoren]

I took a deeper look at the custom merge logic in RawFieldMappingMerge and agree that passing on "null" in the recursion when the parent is a "properties" field should not affect any further merging logic down the line.

Thanks for verifying 🙏
Maybe another way to put it is that XContentHelper.merge() provides tree-merge functionality and the optional parent argument can be used to add context for the merge if necessary. When merging mapping subtrees of a field, we only need the plain merge functionality, so this additional context is not required.
Therefore, there is already a merge API to do just that, so I just merged a tiny change to use it instead. I think it makes it a bit cleaner. I am asking for a re-review just as sanity check.

[felixbarny]

Just a nit on a comment, otherwise LGTM

[felixbarny]

Tip: you can apply the auto-backport-and-merge label so that the PR automatically gets back ported to 8.14.1 after it is merged.

[elasticsearchmachine]

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[eyalkoren]

💚 All backports created successfully

Status	Branch	Result
✅	8.14

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