Spring Data REST fails when setting version to openapi_3_1

[clementdenis]

Describe the bug

When enabling OpenAPI 3.1 on a Spring Data REST project, we're getting this error due a :

java.lang.ClassCastException: class io.swagger.v3.oas.models.media.JsonSchema cannot be cast to class io.swagger.v3.oas.models.media.ObjectSchema (io.swagger.v3.oas.models.media.JsonSchema and io.swagger.v3.oas.models.media.ObjectSchema are in unnamed module of loader 'app')
	at org.springdoc.core.utils.SpringDocDataRestUtils.updateResponseSchemaEmbedded(SpringDocDataRestUtils.java:283)
	at org.springdoc.core.utils.SpringDocDataRestUtils.updateResponseSchema(SpringDocDataRestUtils.java:266)
	at org.springdoc.core.utils.SpringDocDataRestUtils.lambda$updateApiResponse$3(SpringDocDataRestUtils.java:168)
	at java.base/java.util.HashMap$KeySet.forEach(HashMap.java:1016)
	at org.springdoc.core.utils.SpringDocDataRestUtils.lambda$updateApiResponse$4(SpringDocDataRestUtils.java:166)
	at java.base/java.util.LinkedHashMap$LinkedValues.forEach(LinkedHashMap.java:833)
	at org.springdoc.core.utils.SpringDocDataRestUtils.updateApiResponse(SpringDocDataRestUtils.java:161)
	at org.springdoc.core.utils.SpringDocDataRestUtils.lambda$customise$0(SpringDocDataRestUtils.java:145)
	at java.base/java.util.LinkedHashMap.forEach(LinkedHashMap.java:986)
	at org.springdoc.core.utils.SpringDocDataRestUtils.lambda$customise$1(SpringDocDataRestUtils.java:145)
	at java.base/java.util.ArrayList.forEach(ArrayList.java:1596)
	at org.springdoc.core.utils.SpringDocDataRestUtils.lambda$customise$2(SpringDocDataRestUtils.java:140)
	at java.base/java.util.Iterator.forEachRemaining(Iterator.java:133)
	at java.base/java.util.Spliterators$IteratorSpliterator.forEachRemaining(Spliterators.java:1939)
	at java.base/java.util.stream.ReferencePipeline$Head.forEach(ReferencePipeline.java:762)
	at org.springdoc.core.utils.SpringDocDataRestUtils.customise(SpringDocDataRestUtils.java:138)
	at org.springdoc.core.providers.SpringRepositoryRestResourceProvider.customize(SpringRepositoryRestResourceProvider.java:314)
	at org.springdoc.webmvc.api.OpenApiResource.lambda$getPaths$1(OpenApiResource.java:156)
	at java.base/java.util.Optional.ifPresent(Optional.java:178)
	at org.springdoc.webmvc.api.OpenApiResource.lambda$getPaths$2(OpenApiResource.java:153)
	at java.base/java.util.Optional.ifPresent(Optional.java:178)
	at org.springdoc.webmvc.api.OpenApiResource.getPaths(OpenApiResource.java:149)
	at org.springdoc.api.AbstractOpenApiResource.getOpenApi(AbstractOpenApiResource.java:353)
	at org.springdoc.webmvc.api.OpenApiResource.openapiJson(OpenApiResource.java:124)
	at org.springdoc.webmvc.api.OpenApiWebMvcResource.openapiJson(OpenApiWebMvcResource.java:111)

To Reproduce
Steps to reproduce the behavior:

• Set up a Spring Data REST project with Springdoc
• Check it works using openapi_3_0
• Change version to openapi_3_1
  => getting a ClassCastException

Expected behavior

• The spec generation should work

Additional context

Seems the casting to ObjectSchema is not necessary here, removing it would fix the issue:

springdoc-openapi/springdoc-openapi-starter-common/src/main/java/org/springdoc/core/utils/SpringDocDataRestUtils.java

Line 284 in 765607d

ArraySchema arraySchema = (ArraySchema) ((ObjectSchema) entry.getValue()).getProperties().get(entityClassName);

[clementdenis]

This is still not working after the first fix, there's still a CCE on the same line
=> the arraySchema is actually a JsonSchema, not an ArraySchema.

Simplest would be to just cast it to the base Schema class:
Schema<?> arraySchema = (Schema) entry.getValue().getProperties().get(entityClassName);

But even after applying this, I still have some issues with 3.1: my OpenAPI spec is missing some schema.
=> I will try to investigate and open a new issue with my findings.

java.lang.ClassCastException: class io.swagger.v3.oas.models.media.JsonSchema cannot be cast to class io.swagger.v3.oas.models.media.ArraySchema (io.swagger.v3.oas.models.media.JsonSchema and io.swagger.v3.oas.models.media.ArraySchema are in unnamed module of loader 'app')
	at org.springdoc.core.utils.SpringDocDataRestUtils.updateResponseSchemaEmbedded(SpringDocDataRestUtils.java:283)
	at org.springdoc.core.utils.SpringDocDataRestUtils.updateResponseSchema(SpringDocDataRestUtils.java:266)
	at org.springdoc.core.utils.SpringDocDataRestUtils.lambda$updateApiResponse$3(SpringDocDataRestUtils.java:168)
	at java.base/java.util.HashMap$KeySet.forEach(HashMap.java:1016)
	at org.springdoc.core.utils.SpringDocDataRestUtils.lambda$updateApiResponse$4(SpringDocDataRestUtils.java:166)
	at java.base/java.util.LinkedHashMap$LinkedValues.forEach(LinkedHashMap.java:833)
	at org.springdoc.core.utils.SpringDocDataRestUtils.updateApiResponse(SpringDocDataRestUtils.java:161)
	at org.springdoc.core.utils.SpringDocDataRestUtils.lambda$customise$0(SpringDocDataRestUtils.java:145)
	at java.base/java.util.LinkedHashMap.forEach(LinkedHashMap.java:986)
	at org.springdoc.core.utils.SpringDocDataRestUtils.lambda$customise$1(SpringDocDataRestUtils.java:145)
	at java.base/java.util.ArrayList.forEach(ArrayList.java:1596)
	at org.springdoc.core.utils.SpringDocDataRestUtils.lambda$customise$2(SpringDocDataRestUtils.java:140)
	at java.base/java.util.Iterator.forEachRemaining(Iterator.java:133)
	at java.base/java.util.Spliterators$IteratorSpliterator.forEachRemaining(Spliterators.java:1939)
	at java.base/java.util.stream.ReferencePipeline$Head.forEach(ReferencePipeline.java:762)
	at org.springdoc.core.utils.SpringDocDataRestUtils.customise(SpringDocDataRestUtils.java:138)
	at org.springdoc.core.providers.SpringRepositoryRestResourceProvider.customize(SpringRepositoryRestResourceProvider.java:314)
	at org.springdoc.webmvc.api.OpenApiResource.lambda$getPaths$1(OpenApiResource.java:156)
	at java.base/java.util.Optional.ifPresent(Optional.java:178)
	at org.springdoc.webmvc.api.OpenApiResource.lambda$getPaths$2(OpenApiResource.java:153)
	at java.base/java.util.Optional.ifPresent(Optional.java:178)
	at org.springdoc.webmvc.api.OpenApiResource.getPaths(OpenApiResource.java:149)
	at org.springdoc.api.AbstractOpenApiResource.getOpenApi(AbstractOpenApiResource.java:353)
	at org.springdoc.webmvc.api.OpenApiResource.openapiJson(OpenApiResource.java:124)
	at org.springdoc.webmvc.api.OpenApiWebMvcResource.openapiJson(OpenApiWebMvcResource.java:114)
	at org.springdoc.webmvc.api.MultipleOpenApiWebMvcResource.openapiJson(MultipleOpenApiWebMvcResource.java:95)