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https://issues.apache.org/jira/browse/GROOVY-11508?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17892872#comment-17892872
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Eric Milles commented on GROOVY-11508:
--------------------------------------

"Also, since GROOVY-5106 breaks backwards compatibility with Groovy 3.x, it 
would make sense for this to be a warning in Groovy 4 & a restriction in Groovy 
5 instead."

Since this checking was introduced in 4.0.0, the error was the correct choice 
IMO.  There have been 23 point fixes since...  So I have a different take on 
the criticality.

I will have a look at "abstract static" methods and static members referencing 
type vars in traits for Eclipse IDE integration.  Not too sure how I can 
represent these things to the Java model -- the parallel would be the stubs 
that the Groovy compiler generates in joint compilation mode.

> Multiple traits with related generic types cannot be used
> ---------------------------------------------------------
>
>                 Key: GROOVY-11508
>                 URL: https://issues.apache.org/jira/browse/GROOVY-11508
>             Project: Groovy
>          Issue Type: Bug
>          Components: Compiler
>    Affects Versions: 4.0.0
>            Reporter: James Daugherty
>            Assignee: Eric Milles
>            Priority: Major
>         Attachments: screenshot-1.png, screenshot-2.png, screenshot-3.png
>
>
> 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|https://github.com/grails/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:
> {code:java}
> class Parent extends GormEntity<Parent> {
> }
> class Child extends GormEntity<Child> {
> } 
> class GormEntity<? extends GormEntity> { // ? extends GormEntity is not 
> allowed
> }{code}
>  
> 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:
> {code:java}
> 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()
> }
>  {code}
> This allows someone to do the following in code:
> {code:java}
> Parent.get(1L) // Will find either a Child or Parent
> Child.get(1L) // Will find only child types{code}
>  
> 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?



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