[jira] [Commented] (GROOVY-11035) Inferred type is Object when having a complex inheritance chain of interfaces

["Eric Milles (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/GROOVY-11035?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17718058#comment-17718058 ] 

Eric Milles commented on GROOVY-11035:
--------------------------------------

Like with Guava, this is a case of a bridge method that lacks generics information:
{code}
// Method descriptor #47 ()Ljava/lang/Object;
  // Stack: 1, Locals: 1
  public bridge synthetic java.lang.Object next();
    0  aload_0 [this]
    1  invokespecial org.apache.commons.collections4.iterators.AbstractEmptyIterator.next() : java.lang.Object [12]
    4  areturn
      Line numbers:
        [pc: 0, line: 32]
      Local variable table:
        [pc: 0, pc: 5] local: this index: 0 type: org.apache.commons.collections4.iterators.EmptyListIterator
      Local variable type table:
        [pc: 0, pc: 5] local: this index: 0 type: org.apache.commons.collections4.iterators.EmptyListIterator<E>
{code}

We had to stick with the bridge/synthetic methods because the provide the necessary accessibility/visibility for Java 16+.  I'm not sure what java compilers do in this circumstance, but the return type that is directly available is just Object.

https://github.com/apache/commons-collections/blob/master/src/main/java/org/apache/commons/collections4/iterators/EmptyListIterator.java

> Inferred type is Object when having a complex inheritance chain of interfaces
> -----------------------------------------------------------------------------
>
>                 Key: GROOVY-11035
>                 URL: https://issues.apache.org/jira/browse/GROOVY-11035
>             Project: Groovy
>          Issue Type: Bug
>          Components: Static Type Checker
>            Reporter: Thodoris Sotiropoulos
>            Assignee: Eric Milles
>            Priority: Minor
>
> This seems related to GROOVY-11012.
> I have the following program
> {code}
> @Grab('org.apache.commons:commons-collections4:4.4')
> import org.apache.commons.collections4.iterators.*;
> class Main {
>   @groovy.transform.TypeChecked test() {
>     EmptyListIterator<Number> tmp = null
>     Number x = tmp.next()
>   }
> }
> {code}
> h3. Actual behavior
> {code}
> org.codehaus.groovy.control.MultipleCompilationErrorsException: startup failed:
> test.groovy: 6: [Static type checking] - Cannot assign value of type java.lang.Object to variable of type java.lang.Number
>  @ line 6, column 16.
>        Number x = tmp.next();
>                   ^
> 1 error
> {code}
> h3. Expected behavior 
> Compile successfully
> h3. Notes
> Tested against master (commit: ed4b33c8d5ac71ee4963d6bb391850593c59e5b1)
> https://commons.apache.org/proper/commons-collections/javadocs/api-4.4/org/apache/commons/collections4/iterators/EmptyListIterator.html



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