JSpecifyMode: function returning a @Nullable is incorrectly handled

[nvervelle]

Hello, it's probably related to #1532 , but as I'm not entirely sure, I prefer to open a dedicated issue (feel free to close it if it's the same underlying problem).

I've tried activating JSpecifyMode in my project and I encounter the following false positive

    return webClient
        .post()
        .uri(properties.accessUrl())
        .contentType(MediaType.APPLICATION_FORM_URLENCODED)
        .body(BodyInserters.fromFormData(formData))
        .retrieve()
        .toEntity(JsonNode.class)
        .mapNotNull(ResponseEntity::getBody)
        .mapNotNull(this::updateAccessToken)
        .switchIfEmpty(Mono.error(() -> new IllegalStateException("Unable to get access token")));

The error message is

error: [NullAway] referenced method returns @Nullable, but functional interface method java.util.function.Function.apply(T) returns @NonNull
          .mapNotNull(ResponseEntity::getBody)

but ResponseEntity.getBody() (from org.springframework.http.ResponseEntity) is defined as

  public @Nullable T getBody() {
    return this.body;
  }

and Mono.mapNotNull() is defined as

  public final <R> Mono<R> mapNotNull(Function <? super T, ? extends @Nullable R> mapper) {
    ...
  }

[msridhar]

Hi @nvervelle can you point me at your project so I can try it, or some reproducer? This is probably related to wildcards, and we've done a lot of work to improve support for them, but it's off by default right now. I'd like to see if that support fixes this one.

[nvervelle]

Hi @msridhar , thanks for the quick answer.

Sorry, the project is not publicly available, it's for my company. Is there an option to enable the improvement for wildcards support on my side to try it directly ?

Otherwise, I can try producing a reproducible small example, but not immediately.

[nvervelle]

Hi @msridhar .

In fact, it was easy

package testjspecify;

import org.springframework.http.ResponseEntity;
import org.springframework.web.reactive.function.client.WebClient;
import reactor.core.publisher.Mono;
import tools.jackson.databind.JsonNode;

public class TestJSpecify1671 {

  public static Mono<String> testJSpecify() {
    return WebClient.create()
        .post()
        .uri("https://example.com")
        .retrieve()
        .toEntity(JsonNode.class)
        .mapNotNull(ResponseEntity::getBody)
        .mapNotNull(jsonNode -> jsonNode.get("access_token").asString())
        .switchIfEmpty(Mono.error(() -> new IllegalStateException("Unable to get access token")));
  }
}

Error:

.../TestJSpecify1671.java:16: error: [NullAway] referenced method returns @Nullable, but functional interface method java.util.function.Function.apply(T) returns @NonNull
        .mapNotNull(ResponseEntity::getBody)
                    ^

Versions:

• spring 7.0.8
• reactor 3.8.6
• jackson 3.1.4

[msridhar]

I've confirmed this issue is fixed on the latest master branch with our wildcard support enabled. I'll work on getting this support out into a release soon. I still don't recommend enabling the wildcard support with the current release.