Wrong type signature in method chaining

[cagritepebasili]

Compiler version

Scala Version: 3.2.1

Minimized code

dependencies:

Maven dependencies:

<dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>io.projectreactor</groupId>
                <artifactId>reactor-bom</artifactId>
                <version>2020.0.6</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
</dependencyManagement>

<dependency>
            <groupId>io.projectreactor.netty</groupId>
            <artifactId>reactor-netty-core</artifactId>
        </dependency>
        <dependency>
            <groupId>io.projectreactor.netty</groupId>
            <artifactId>reactor-netty-http</artifactId>
</dependency>

HttpClient.create().get().uri("").responseContent().aggregate().asString()

Output

value responseContent is not a member of reactor.netty.http.client.HttpClient#ResponseReceiver'

Expectation

This code doesn't compile due to 'value responseContent is not a member of reactor.netty.http.client.HttpClient#ResponseReceiver'. Same code compiles in Java. What am I missing ?

Interesting note that, I got error highlights for this piece of code in Intellij IDEA but it was worked in Scala 2.13.x anyway. I upgraded Scala version to 3 and this code no longer compiles.

Also i get same errors in some Spring Framework methods. Somehow in method chaining interface types get lost. This issue #16724 might be related with this.

scala-netty-reactor.zip

[anatoliykmetyuk]

It would be good to have a minimized version without external dependencies.

[cagritepebasili]

I would love to give you a minimized version of this but I don't know what causes this bug. So I cannot produce a minimized version of this problem.

As I mentioned:

HttpClient.create().get().uri("").responseContent().aggregate().asString()

Above line is perfectly valid code. I can compile it with Scala 2.13.x. But it doesn't compile with Scala version 3.2.1.

[wjoel]

Here's an attempt at a minimized example, fails to compile with the error message

Compiling project (Scala 3.5.0, JVM (22))
[error] ./Main.scala:3:3
[error] value responseContent is not a member of HttpClient#ResponseReceiver[?]#A
[error]   HttpClient.create().get().uri("").responseContent()
[error]   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Error compiling project (Scala 3.5.0, JVM (22))

public abstract class HttpClient {
  public interface UriConfiguration<A extends UriConfiguration<?>> {
    A uri(String uri);
  }

  public interface ResponseReceiver<B extends ResponseReceiver<?>> extends UriConfiguration<B> {
    String responseContent();
  }

  public final ResponseReceiver<?> get() {
    return null;
  }

  public static HttpClient create() {
    return new HttpClient() { };
  }
}

object Main {
  HttpClient.create().get().uri("").responseContent() // error on Scala 3, works on Scala 2
}

The closest I could get with only Scala code is this, giving the same kind of error message on Scala 3 (value responseContent is not a member of HttpClientS.ResponseReceiver[?]#A), but does not compile on Scala 2.13 either (value responseContent is not a member of ?$3):

object HttpClientS {
  trait UriConfiguration[A <: UriConfiguration[?]] {
    def uri(uri: String): A
  }

  trait ResponseReceiver[B <: ResponseReceiver[?]]
    extends UriConfiguration[B] {
    def responseContent(): String
  }

  abstract class HttpClientS {
    def get(): ResponseReceiver[?] = ???
  }

  def create() = {
    new HttpClientS() { }
  }
}

[wjoel]

Huh. Using some self-types, HttpClientS.create().get().uri("").responseContent() works with this:

object HttpClientS {
  trait UriConfiguration[A <: UriConfiguration[?]] { base: A =>
    def uri(uri: String): base.type
  }

  trait ResponseReceiver[B <: ResponseReceiver[?]]
    extends UriConfiguration[B] { base: B =>
    def responseContent(): String
  }

  abstract class HttpClientS {
    def get(): ResponseReceiver[?] = ???
  }

  def create() = {
    new HttpClientS() { }
  }
}