MapperBuilderContext#isDataStream is incorrect when handling mapping updates

[lkts]

Elasticsearch Version

8.15

Installed Plugins

No response

Java Version

bundled

OS Version

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Problem Description

See #110603 (comment).

Steps to Reproduce

1. Create a time series mode index with default mapping only
2. Update mapping with {"@timestamp": {"type": "date"}} (or anything really)

For this mapping update isDataStream is false even though it was true when index was created.

Logs (if relevant)

No response

[elasticsearchmachine]

Pinging @elastic/es-storage-engine (Team:StorageEngine)

[elasticsearchmachine]

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

[javanna]

I stumbled upon this too quite recently. This is similar to another issue I fixed with #109963 caused by not propagating flags to the MapperBuilderContext constructor.

I could not tell for sure if this is a problem or not, given where isDataStream is used. I also have suspicions that this may end up causing #107760 . I can see that you found this problem as part of extending where isDataStream was used, was that it or did you see additional issues?

[lkts]

So far i have only had problems with this in #110603 and i ended up working around it.