HATOEAS Links produces a circular reference

[twobiers]

Describe the bug
When using springodc-openapi-hateoas in a Spring Boot HATEOAS project the generated OpenAPI Schema of the HATEOAS Links object is a circular reference to itself.

To Reproduce

Steps to reproduce the behavior:
I am using the following Dependencies:

<dependency>
      <groupId>org.springdoc</groupId>
      <artifactId>springdoc-openapi-ui</artifactId>
      <version>1.5.2</version>
    </dependency>
    <dependency>
      <groupId>org.springdoc</groupId>
      <artifactId>springdoc-openapi-webmvc-core</artifactId>
      <version>1.5.2</version>
    </dependency>
    <dependency>
      <groupId>org.springdoc</groupId>
      <artifactId>springdoc-openapi-hateoas</artifactId>
      <version>1.5.2</version>
    </dependency>
    <dependency>
      <groupId>org.springdoc</groupId>
      <artifactId>springdoc-openapi-security</artifactId>
      <version>1.5.2</version>
    </dependency>

And a simple HATEOAS controller like this:

@RestController
public class FooController {

  private final FooService fooService;
  private final FooRepresentationModelAssembler fooRepresentationModelAssembler;

  @Autowired
  public FooController(
      FooService fooService,
      FooRepresentationModelAssembler fooRepresentationModelAssembler) {
    this.fooService = fooService;
    this.fooRepresentationModelAssembler = fooRepresentationModelAssembler;
  }

  @GetMapping(value = "foo/{id}", produces = MediaTypes.HAL_JSON_VALUE)
  public ResponseEntity<EntityModel<Foo>> getFoo(@PathVariable("id") UUID id) throws Exception {
    var foo = fooService.getFoo(id).orElseThrow(Exception::new);
    return ResponseEntity.ok(fooRepresentationModelAssembler.toModel(foo));
  }
}

Springdoc generates the following Schema definition:

{
   "EntityModelFoo":{
      "type":"object",
      "properties":{
         "_links": {
            "$ref":"#/components/schemas/Links"
         }
      }
   },
   "Links":{
      "$ref": "#/components/schemas/Links",
   }
}

Expected behavior
I would expect the schema to be like this:

{
   "EntityModelFoo":{
      "type":"object",
      "properties":{
         "links":{
            "type":"array",
            "items":{
               "$ref":"#/components/schemas/Link"
            }
         }
      }
   },
   "Link":{
      "type":"object",
      "properties":{
         "rel":{
            "type":"string"
         },
         "href":{
            "type":"string"
         },
         "hreflang":{
            "type":"string"
         },
         "media":{
            "type":"string"
         },
         "title":{
            "type":"string"
         },
         "type":{
            "type":"string"
         },
         "deprecation":{
            "type":"string"
         },
         "profile":{
            "type":"string"
         },
         "name":{
            "type":"string"
         }
      }
   }
}

Additional context
For me this is a problem as the OpenAPI Generator will produce a StackOverflow Error.

[twobiers]

As I started to create an example repository it turns out, that the problem was due to my configuration of the package-scan scope, I had the following Bean Configuration:

@Bean
public GroupedOpenApi userOpenApi() {
  String packagesToscan[] = {"de.foo.application"};
  return GroupedOpenApi.builder().group("foo-service").packagesToScan(packagesToscan).build();
}

However this causes springdoc to be not able to retrieve the HATEOAS Link Mapping correctly but only inside the group definition - the root definition is okay. I wonder if this is intentioned so I will leave the issue open for now.

Here is my example repository: https://github.com/tobi6112/springdoc-issue-demo

[bnasslahsen]

Hi @tobi6112,

Thank for reporting this issue and your clear description.
The cause of this behavior, is that while using a group a spring HATEOAS OpenApiCustomiser, was not picked in the group level.

This is a workaround code with 1.5.2 with groups:

@Bean
public GroupedOpenApi userOpenApi(HateoasHalProvider halProvider, SpringDocConfigProperties springDocConfigProperties) {
	String packagesToscan[] = { "demo.application" };
	return GroupedOpenApi.builder().group("foo-service").packagesToScan(packagesToscan)
			.addOpenApiCustomiser(linksSchemaCustomiser(halProvider,springDocConfigProperties))
			.build();
}

OpenApiCustomiser linksSchemaCustomiser(HateoasHalProvider halProvider, SpringDocConfigProperties springDocConfigProperties) {
	if (!halProvider.isHalEnabled()) {
		return openApi -> {
		};
	}
	Json.mapper().addMixIn(RepresentationModel.class, RepresentationModelLinksOASMixin.class);
	return new OpenApiHateoasLinksCustomiser(springDocConfigProperties);
}

A fix, to make this OpenApiCustomiser picked by default will be added for the next release.