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  1. JDK
  2. JDK-8177520

Type inference "varargs mismatch; inference variable R has incompatible bounds"

    Details

    • Subcomponent:
    • Introduced In Build:
      b22
    • Introduced In Version:
      9
    • CPU:
      generic
    • OS:
      generic

      Description

      FULL PRODUCT VERSION :
      java version "9-ea"
      Java(TM) SE Runtime Environment (build 9-ea+161)
      Java HotSpot(TM) 64-Bit Server VM (build 9-ea+161, mixed mode)

      ADDITIONAL OS VERSION INFORMATION :
      not OS specific (currently reproducing on Darwin syrah 16.4.0 Darwin Kernel Version 16.4.0: Thu Dec 22 22:53:21 PST 2016; root:xnu-3789.41.3~3/RELEASE_X86_64 x86_64)

      A DESCRIPTION OF THE PROBLEM :
      See the code, compiles with JDK8 alright, fails with latest JDK9 161.

      /Users/rhusar/wildfly/clustering/jgroups/extension/src/main/java/org/jboss/as/clustering/jgroups/JChannelFactory.java:[68,13] error: no suitable method found for addProtocols(List<Object>)
          method ProtocolStack.addProtocols(Protocol...) is not applicable
            (varargs mismatch; inference variable R has incompatible bounds
                equality constraints: List<T#2>
                upper bounds: Protocol,Object)
          method ProtocolStack.addProtocols(List<Protocol>) is not applicable
            (argument mismatch; inference variable T#2 has incompatible bounds
                equality constraints: Protocol
                lower bounds: Object)
        where R,A,T#1,T#2 are type-variables:
          R extends Object declared in method <R,A>collect(Collector<? super T#1,A,R>)
          A extends Object declared in method <R,A>collect(Collector<? super T#1,A,R>)
          T#1 extends Object declared in interface Stream
          T#2 extends Object declared in method <T#2>toList()
      [ERROR] /Users/rhusar/wildfly/clustering/jgroups/extension/src/main/java/org/jboss/as/clustering/jgroups/JChannelFactory.java:[72,76] error: cannot find symbol
        symbol: method createProtocol(ProtocolStackConfiguration)
        location: variable pc of type Object

      STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
      see code

      EXPECTED VERSUS ACTUAL BEHAVIOR :
      EXPECTED -
      the test attached compiles OK like jdk9
      ACTUAL -
      [ERROR] COMPILATION ERROR :
      [INFO] -------------------------------------------------------------
      [ERROR] /Users/rhusar/git/jdk9typebug/src/main/java/JChannelFactory.java:[14,14] no suitable method found for addProtocols(java.util.List<java.lang.Object>)
          method JChannelFactory.ProtocolStack.addProtocols(JChannelFactory.Protocol...) is not applicable
            (varargs mismatch; inference variable R has incompatible bounds
                equality constraints: java.util.List<T>
                upper bounds: JChannelFactory.Protocol,java.lang.Object)
          method JChannelFactory.ProtocolStack.addProtocols(java.util.List<JChannelFactory.Protocol>) is not applicable
            (argument mismatch; inference variable T has incompatible bounds
                equality constraints: JChannelFactory.Protocol
                lower bounds: java.lang.Object)
      [ERROR] /Users/rhusar/git/jdk9typebug/src/main/java/JChannelFactory.java:[17,77] cannot find symbol
        symbol: method createProtocol(JChannelFactory.ProtocolStackConfiguration)
        location: variable pc of type java.lang.Object
      [INFO] 2 errors

      REPRODUCIBILITY :
      This bug can be reproduced always.

      ---------- BEGIN SOURCE ----------
      import java.util.List;
      import java.util.Objects;
      import java.util.function.Function;
      import java.util.stream.Collectors;
      import java.util.stream.Stream;

      /**
       * @author Radoslav Husar
       */
      public class JChannelFactory {
          void createChannel() {
              ProtocolStackConfiguration configuration = new ProtocolStackConfiguration();
              ProtocolStack stack = new ProtocolStack();
              stack.addProtocols(Stream.of(
                      Stream.of(configuration.getTransport()),
                      configuration.getProtocols().stream()
              ).flatMap(Function.identity()).filter(Objects::nonNull).map(pc -> pc.createProtocol(configuration)).collect(Collectors.toList()));
          }

          public abstract static class Protocol {
          }

          public interface ProtocolConfiguration<P extends Protocol> {
              P createProtocol(ProtocolStackConfiguration stackConfiguration);
          }

          static class ProtocolStackConfiguration {

              ProtocolConfiguration<? extends TP> getTransport() {
                  return null;
              }

              List<ProtocolConfiguration<? extends Protocol>> getProtocols() {
                  return null;
              }
          }

          static class TP extends Protocol {
          }

          public static class ProtocolStack {

              public ProtocolStack addProtocols(Protocol... prots) {
                  return this;
              }

              public ProtocolStack addProtocols(List<Protocol> prots) {
                  return this;
              }

          }
      }

      ---------- END SOURCE ----------

      CUSTOMER SUBMITTED WORKAROUND :
      explicitly cast:

      .map(pc -> ((ProtocolConfiguration)pc).createProtocol(configuration))

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              • Assignee:
                dlsmith Dan Smith
                Reporter:
                webbuggrp Webbug Group
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                • Created:
                  Updated:
                  Resolved: