Index.updateSettings with filterableAttributesConfig fails with Jackson

[jebbench]

Description
When using the filterableAttributesConfig settings property an exception is thrown.

It looks like Jackson is attempting to serialise the Settings.getFilterableAttributes accessor causing it to throw a "don't use me" exception.

Example Code

val idx = meili.index(INDEX_NAME)
idx.updateSettings(Settings().apply {
    filterableAttributesConfig = arrayOf(
        FilterableAttributesConfig(arrayOf("parent"), FilterableAttributesFeatures().apply {
            filter = FilterableAttributesFilter(true, false)
            facetSearch = false
        }),
        FilterableAttributesConfig(arrayOf("other", "third"), FilterableAttributesFeatures().apply {
            filter = FilterableAttributesFilter(true, true)
            facetSearch = false
        })
    )
})

Exception

java.lang.RuntimeException: Meilisearch Exception: {com.fasterxml.jackson.databind.JsonMappingException. Error=com.fasterxml.jackson.databind.JsonMappingException: This index uses granular filterable attributes; please use the granular filterable attributes methods instead of the legacy String[] API. (through reference chain: com.meilisearch.sdk.model.Settings["filterableAttributes"])}
	at com.meilisearch.sdk.http.request.BasicRequest.create(BasicRequest.java:22)
	at com.meilisearch.sdk.HttpClient.patch(HttpClient.java:135)
	at com.meilisearch.sdk.SettingsHandler.updateSettings(SettingsHandler.java:54)
	at com.meilisearch.sdk.Index.updateSettings(Index.java:596)
	at dev.r36.mercury.rulebot.search.AgentSearchClient.initialise(AgentSearchClient.kt:40)
	at dev.r36.mercury.rulebot.search.BulkCreateEmbeddingsKt$main$1.invokeSuspend(BulkCreateEmbeddings.kt:32)
	at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:34)
	at kotlinx.coroutines.DispatchedTask.run(DispatchedTask.kt:100)
	at kotlinx.coroutines.EventLoopImplBase.processNextEvent(EventLoop.common.kt:263)
	at kotlinx.coroutines.BlockingCoroutine.joinBlocking(Builders.kt:94)
	at kotlinx.coroutines.BuildersKt__BuildersKt.runBlocking(Builders.kt:70)
	at kotlinx.coroutines.BuildersKt.runBlocking(Unknown Source)
	at kotlinx.coroutines.BuildersKt__BuildersKt.runBlocking$default(Builders.kt:48)
	at kotlinx.coroutines.BuildersKt.runBlocking$default(Unknown Source)
	at dev.r36.mercury.rulebot.search.BulkCreateEmbeddingsKt.main(BulkCreateEmbeddings.kt:25)
	at dev.r36.mercury.rulebot.search.BulkCreateEmbeddingsKt.main(BulkCreateEmbeddings.kt)
Caused by: com.meilisearch.sdk.exceptions.JsonEncodingException: com.fasterxml.jackson.databind.JsonMappingException: This index uses granular filterable attributes; please use the granular filterable attributes methods instead of the legacy String[] API. (through reference chain: com.meilisearch.sdk.model.Settings["filterableAttributes"])
	at com.meilisearch.sdk.json.JacksonJsonHandler.encode(JacksonJsonHandler.java:48)
	at com.meilisearch.sdk.http.request.BasicRequest.create(BasicRequest.java:20)
	... 15 more
Caused by: com.fasterxml.jackson.databind.JsonMappingException: This index uses granular filterable attributes; please use the granular filterable attributes methods instead of the legacy String[] API. (through reference chain: com.meilisearch.sdk.model.Settings["filterableAttributes"])
	at com.fasterxml.jackson.databind.JsonMappingException.wrapWithPath(JsonMappingException.java:400)
	at com.fasterxml.jackson.databind.JsonMappingException.wrapWithPath(JsonMappingException.java:359)
	at com.fasterxml.jackson.databind.ser.std.StdSerializer.wrapAndThrow(StdSerializer.java:324)
	at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:765)
	at com.fasterxml.jackson.databind.ser.BeanSerializer.serialize(BeanSerializer.java:183)
	at com.fasterxml.jackson.databind.ser.DefaultSerializerProvider._serialize(DefaultSerializerProvider.java:503)
	at com.fasterxml.jackson.databind.ser.DefaultSerializerProvider.serializeValue(DefaultSerializerProvider.java:342)
	at com.fasterxml.jackson.databind.ObjectMapper._writeValueAndClose(ObjectMapper.java:4938)
	at com.fasterxml.jackson.databind.ObjectMapper.writeValueAsString(ObjectMapper.java:4146)
	at com.meilisearch.sdk.json.JacksonJsonHandler.encode(JacksonJsonHandler.java:46)
	... 16 more
Caused by: com.meilisearch.sdk.exceptions.GranularFilterableAttributesException: This index uses granular filterable attributes; please use the granular filterable attributes methods instead of the legacy String[] API.
	at com.meilisearch.sdk.model.FilterableAttributesLegacyAdapter.toLegacyNamesOrThrow(FilterableAttributesLegacyAdapter.java:51)
	at com.meilisearch.sdk.model.Settings.getFilterableAttributes(Settings.java:56)
	at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:104)
	at java.base/java.lang.reflect.Method.invoke(Method.java:565)
	at com.fasterxml.jackson.databind.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:688)
	at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:760)
	... 22 more

Environment (please complete the following information):

• OS: Windows
• Meilisearch version: 1.48.1
• meilisearch-java version: 0.20.1

[Moustafa-Ameen]

Hi, I’m interested in investigating and fixing this issue.

The stack trace suggests that Jackson is serializing the legacy getFilterableAttributes() accessor even when filterableAttributesConfig is being used, which causes the adapter to throw during Settings serialization.

My plan would be to:

• Reproduce the failure with a focused test using filterableAttributesConfig.
• Review the Jackson annotations and serialization behavior of Settings and the legacy adapter.
• Make the smallest change needed so granular filterable-attribute settings serialize correctly without breaking the legacy String[] API.
• Add regression coverage for both granular and legacy filterable-attribute configurations.

I’ll share the findings or open a focused PR once I have confirmed the correct compatibility approach.