[GROOVY-9500] Goorvy 3 Compilation Failure issue with Generics and same type argument name

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 3.0.1, 3.0.2, 3.0.3
• Component/s: Static compilation
• Assignee: Eric Milles
• Reporter: Puneet Behl
• Created: 09/Apr/20 17:34
• Updated: 08/Mar/22 12:16
• Resolved: 17/Oct/21 18:47

Description

While upgrading GORM for Neo4j to support Groovy 3, we are seeing an issue with generics as:

[Static type checking] - Cannot return value of type grails.neo4j.Path$Segment <S, E> on method returning type T
 @ line 81, column 16.
 return end
 ^

1 error

 

I believe the problem is with using same name of type argument in the Generics for multiple classes as in the following code:

import groovy.transform.CompileStatic
import java.util.function.Consumer

@CompileStatic
abstract class Path<F extends Neo4jEntity, T extends Neo4jEntity> implements Iterable<Segment<F,T>> {

    T end

    interface Segment<F, T> {
        F start()

        T end()
    }

    abstract F start()
    T end() {
        return end
    }

    @Override
    void forEach(Consumer<? super Segment<F, T>> action) { }

    @Override
    Spliterator<Segment<F, T>> spliterator() {
        return null
    }

    @Override
    Iterator<Segment<F, T>> iterator() {
        return null
    }
}

trait Neo4jEntity<D> {

}

println GroovySystem.version

Please note that If we replace `F` and `T` in the above code with `S` and `E` the code will compile successfully.