[GROOVY-10102] Type checking fails when calling trait method using indirect SelfType relation

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 2.5.14
• Fix Version/s: 4.0.0-beta-1, 3.0.9
• Component/s: Compiler, Static Type Checker
• Labels: traits
• Assignee: Eric Milles
• Reporter: Renato Athaydes
• Created: 21/May/21 10:19
• Updated: 22/Sep/22 16:33
• Resolved: 26/May/21 15:06

Description

I am having trouble migrating a very large project from Groovy 2.4.x to 2.5.14.

I was able to reproduce the problem with this small example:
 

import groovy.transform.CompileStatic
 import groovy.transform.SelfType
import java.util.function.Supplier
@CompileStatic
 @SelfType([C])
 trait D {
   def go() {
     String s = foo
     withObject(s) {
       s.toUpperCase()
     }
  }
 }

@SelfType(B)
@CompileStatic
trait C {}

@SelfType([A])
@CompileStatic
trait B {}

@CompileStatic
trait A {
   String foo = 'foo'
  def withObject(String s, Supplier<Object> g) {
     s + g.get()
   }

}

class Impl implements A, B, C, D {
   def go() {

    println withObject(foo) { ' bar' }

  }
 }

 

 
Compiling this code results in this error:

 

src/main/groovy/bar/Foo.groovy: 13: [Static type checking] - Cannot find matching method <UnionType:bar.C+bar.D>#withObject(java.lang.String, groovy.lang.Closure). Please check if the declared type is correct and if the method exists.
 @ line 13, column 9.
 withObject(s) {
 ^

1 error

It's easy to work around once you know how: just make the trait that calls `withObject` list the trait that provides that method in its `SelfType` directly, i.e. in this case:

 

@SelfType([A, C])
trait D { ... } 

 

Interestingly, changing D's self-type to `B` also works! It looks like the 2nd indirection is needed to reproduce the issue.

 

However, figuring it out can take a long time! Would be nice to make this work automatically, maybe by just making `@SelfType(C)` equivalent to `@SelfType(C, B, A)` (i.e. merge the types by recursively applying other's self-types).