MediaTypeConfigurationCustomizer(s) are not applied on HalConfiguration

[vierbergenlars]

spring-hateoas has introduced MediaTypeConfigurationCustomizer, which can be used to configure/modify HalConfiguration and HalFormsConfiguration in an additive way instead of overwriting the whole bean. (see spring-projects/spring-hateoas#2035)

However, these customizers are not applied in spring-data-rest where HalConfiguration or HalFormsConfiguration are used (in RepositoryRestMvcConfiguration), leading to an inconsistency between the configuration as used by spring-hateoas and the one used by spring-data-rest.

I bumped into this because I am using a customizer-based configuration, and its behavior is different when using only spring-hateoas or when having a dependency on spring-data-rest-webmvc (even though it is not being used for this particular endpoint).

	@Bean
	MediaTypeConfigurationCustomizer<HalConfiguration> halConfigurationCustomizer() {
		return halConfiguration -> halConfiguration
				.withRenderSingleLinksFor("supplier", RenderSingleLinks.AS_ARRAY);
	}

Without spring-data-rest-webmvc, the response looks like expected (the supplier link is an array, even though only one link item is present)

{
    "id":null,
    "received":null,
    "supplier":null,
    "_version":0,
    "pay_before":null,
    "total_amount":null,
    "_links":{
        "supplier":[
            {"href":"test"}
        ]
    }
}

When adding a dependency on spring-data-rest-webmvc, the 'render single links' customization seems to get ignored, falling back to the default:

{
  "received" : null,
  "pay_before" : null,
  "total_amount" : null,
  "_links" : {
    "supplier" : {
      "href" : "test"
    }
  }
}

I have an example application displaying the issue here:
invoice-api.zip.
This shows the issue with spring-data-rest-webmvc.
To see the behavior without spring-data-rest-webmvc, either uncomment the exclude line in build.gradle or remove the whole dependeny on the spring-data-rest starter)