[Field_caps] field_caps request don't return fields for indices with readonly_state when include_empty_fields=false

[kertal]

Elasticsearch Version

9.0rc1

Installed Plugins

No response

Java Version

bundled

OS Version

macOS 15.3.2

Problem Description

When requesting field_stats using the param include_empty_fields set to false targeting an index in readonly state, the only fields returned are _tier, _index, _index_mode. There should be much more fields being returned, attaching a screenshot showing the problem with migrated indices from 7.18 -> 9.0rc1:

Originally reported by @jughosta

Steps to Reproduce

• Set an Elasticsearch index to readonly
• Target the index with a field_caps request with the parameter include_empty_fields=false
• The returned resultset just returns a few meta fields

Logs (if relevant)

No response

[elasticsearchmachine]

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

[javanna]

@kertal could you confirm that this is an existing bug for searchable snapshots, possibly since we introduced include_empty_fields? The same bug now affects verified read-only indices as well as they through a similar path.

is there an easy way to mitigate this in Kibana by disabling include_empty_fields ?

[kertal]

@kertal could you confirm that this is an existing bug for searchable snapshots, possibly since we introduced include_empty_fields? The same bug now affects verified read-only indices as well as they through a similar path.

do we have an 8.x instance available with searchable snapshots? I'm not aware of this.

is there an easy way to mitigate this in Kibana by disabling include_empty_fields ?

Sadly, no. We rely in Discover on the results of the include_empty_fields=false to distinguish available from not available fields