[GROOVY-11508] Multiple traits with related generic types cannot be used - ASF JIRA

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Details

Type: Bug
Status: Closed
Priority: Major
Resolution: Fixed
Affects Version/s: 4.0.0
Fix Version/s: 4.0.24
Component/s: Compiler
Labels:
None

Flags:

Patch, Important
Language:
- groovy

Description

When updating Grails from Groovy 3.x to 4.x we discovered that ~~GROOVY-5106~~ prevents us from updating to Groovy 4 for the grails-data-mapping (GORM) project. Groovy-5106 does not take into account relationships between generic types and groovy does not support inheritance in generic types on traits so we have no workable solution for using Groovy 4.

For example, the following is not possible in Groovy 4:

class Parent extends GormEntity<Parent> {

}

class Child extends GormEntity<Child> {

} 

class GormEntity<? extends GormEntity> { // ? extends GormEntity is not allowed

}

We have documented the impacts of this issue on the grails-data-mapping project here: https://github.com/grails/grails-data-mapping/issues/1811 We have discovered that the original change could be reverted and continue to work with the latest Java & Groovy.

For Grails Data Mapping (GORM), there is support for inheritance between a Parent & Child domain object. This is often implemented like this:

class Parent extends GormEntity<Parent> {

}

class Child extends GormEntity<Child> {

}

trait GormEntity<D> { // Simplified for this ticket
    static D get(Serializable id)
   
    static List<D> getAll()
}

This allows someone to do the following in code:

Parent.get(1L) // Will find either a Child or Parent
Child.get(1L) // Will find only child types

Since Groovy-5106 does not take into account inheritance, can this change be reverted or changed to a warning until inheritance is taken into account?