Spring Boot Issue: Missing Bind Errors

Since Boot 2.3 binding errors are no longer included in the default error page by default.

The resolution, until this commit, was to set this property accordingly.

server.error.include-binding-errors=ALWAYS

Unfortunately this no longer works in Boot 3.2.6+.

Expected Behaviour/Repro

Full repro here

Code

@SpringBootApplication
public class DemoApplication {

 public static void main(String[] args) {
    System.setProperty("server.error.include-message", "ALWAYS");
    System.setProperty("server.error.include-binding-errors", "ALWAYS");
		SpringApplication.run(DemoApplication.class, args);
	}

  @RestController
  public static class Controller {

    @GetMapping("/manualBindError")
    public Mono<ResponseEntity<String>> repro() {
      BindException bindException = new BindException(new RuntimeException("error"), "oh oh");
      ObjectError objectError = new ObjectError("oh oh", new String[] {"CODE"}, null, "MESSAGE");
      bindException.addError(objectError);
      throw new ResponseStatusException(400, "a reason", bindException);
    }
  }
}

When we hit http://localhost:8080/manualBindError

Expected

Something resembling the below - with errors intact.

{
  "timestamp": "2024-08-21T13:20:39.377+00:00",
  "path": "/manualBindError",
  "status": 400,
  "error": "Bad Request",
  "message": "a reason",
  "requestId": "d4b54677-3",
  "errors": [
    {
      "codes": [
        "CODE"
      ],
      "arguments": null,
      "defaultMessage": "MESSAGE",
      "objectName": "oh oh",
      "code": "CODE"
    }
  ]
}

Actual

Errors are missing.

{
  "timestamp": "2024-08-21T13:27:27.504+00:00",
  "path": "/manualBindError",
  "status": 400,
  "error": "Bad Request",
  "requestId": "ae84da6d-1",
  "message": "a reason"
}

Root Cause

The code below was removed from DefaultErrorAttributes.

private Throwable determineException(Throwable error) {
	if (error instanceof ResponseStatusException) {
		return (error.getCause() != null) ? error.getCause() : error;
	}
	return error;
}

This is problematic if the cause is an instance of BindingResult as this is no longer true, so the errors aren't added regardless of property value....

private void handleException(Map<String, Object> errorAttributes, Throwable error,
		MergedAnnotation<ResponseStatus> responseStatusAnnotation, boolean includeStackTrace) {
	Throwable exception;
	if (error instanceof BindingResult bindingResult) {
		errorAttributes.put("message", error.getMessage());
		errorAttributes.put("errors", bindingResult.getAllErrors());
		exception = error;
	}

Questions

I can fix this by exposing a custom ErrorAttributes Bean in each app. However, is this the intention or is this a bug? If it's the former then a documentation update would be handy...