[GROOVY-7655] Wrong method is chosen when using super with generics

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 2.4.4
• Fix Version/s: 2.5.0-alpha-1
• Assignee: Jochen Theodorou
• Reporter: Marius Vaitkus
• Created: 02/Nov/15 13:29
• Updated: 29/Mar/17 01:13
• Resolved: 19/Aug/16 14:03

Description

Given code:

generics_extension_test.groovy

interface ParamInterface{}

class ParamImplementation implements ParamInterface{}

class ParamExtension extends ParamImplementation {}

class A<T extends ParamInterface> {

    def getResult(T a) {
        return "A"
    }
}

class B<T extends ParamImplementation> extends A<T> {
    def getResult(T b) {
        return "B"
    }
}

class C extends B<ParamExtension> {
    @Override
    def getResult(ParamExtension b) {
        return super.getResult(b)
    }
}


String result = new C().getResult(new ParamExtension())
assert result == "B"

I get output:

Assertion failed: 

assert result == "B"
       |      |
       A      false

	at generics_extension_test.run(generics_extension_test.groovy:31)

When calling super method, instead of looking for method in a class one hierarchy bellow, groovy goes through complex calculations for finding a better method. I debug'ed up to a point in
groovy.lang.MetaClassImpl#chooseMostSpecificParams
where it turned out that distance for interface was 2 and distance for class that directly extends the method was much bigger, therefore the method from class A is chosen instead of method from class B. However, looking objectively, it would seem that B.getResult is a much better fit:
C extends B and B extends A
parameter hierarchy is shorter (ParamExtension -> ParamImplementation -> ParamInterface)