[jira] [Commented] (GROOVY-8409) Static compilation with generic function wrapping BiFunction causes GroovyCastException

["Shon Vella (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/GROOVY-8409?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16297491#comment-16297491 ] 

Shon Vella commented on GROOVY-8409:
------------------------------------

Since reporting this issue 10 days ago I have run into this same general problem, which is probably best described as the generic type names from the call site getting conflated with scope getting conflated with the generic type names from declaration when CompileStatic is enabled. I've seen it both manifest itself at run time as described in the original bug because of an erroneous call to castTo() and at compile time where it either erroneously flags a type mismatch or can't resolve a property or method because it's trying to do so with the wrong type. 

> Static compilation with generic function wrapping BiFunction causes GroovyCastException
> ---------------------------------------------------------------------------------------
>
>                 Key: GROOVY-8409
>                 URL: https://issues.apache.org/jira/browse/GROOVY-8409
>             Project: Groovy
>          Issue Type: Bug
>          Components: Static compilation
>    Affects Versions: 2.4.8, 2.4.13
>         Environment: MacOS Sierra 10.12.6
>            Reporter: Shon Vella
>         Attachments: Bug.groovy
>
>
> I have a statically compiled with a method declares Generic type T as it's return type and accepts a parameter of type java.util.function.BiFunction also with return type T. It makes a call to the passed in BiFunction and assigns the the result to a variable of type T.
> {code:java}
> static <T> T actionWrapperT(BiFunction<Date, URL, T> action) {
>         T result = action.apply(new Date(), new URL('http://www.example.com'))
>         // do something else here
>         return result
>     }
> {code}
> When actionWrapperT is called with runtime type of T as something other the Date, it causes a GroovyCastException.
> {panel}
> org.codehaus.groovy.runtime.typehandling.GroovyCastException: Cannot cast object 'XXX@71b1176b' with class 'XXX' to class 'java.util.Date'
> {panel}
> because it incorrectly tries to cast result type Date rather than to .
> It appears to me that the compiler is conflating generic type T as declared for the generic method with generic type T as declared by BiFunction<T,U,R> because if I change the name of the generic type of the generic method to R (to match the return type name of BiFunction) or to some other name not used by BiFunction, then it works correctly, but if I change it to U to match the second parameter of the BiFunction then it fails trying to cast to the BiFunction generic type U instead of the method generic type U.
> Problem does not happen under normal compilation or with only type checking enabled.
> Attached file Bug.groovy reproduces the problem.



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