[GROOVY-10749] STC: closure/lambda/reference parameter as type witness for SAM type generics

• Type: Bug
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Fix Version/s: 4.0.5, 2.5.19, 3.0.13
• Assignee: Eric Milles
• Reporter: Eric Milles
• Created: 04/Sep/22 14:45
• Updated: 03/Jan/24 20:13
• Resolved: 04/Sep/22 16:48

Description

Consider the following:

import java.util.function.*
import java.util.stream.*
import groovy.transform.*
class Named {
  String name
}
@TypeChecked
void test() {
  def c1 = Collectors.groupingBy(Named::getName)
  def c2 = Collectors.groupingBy(Named.&getName)
  def c3 = Collectors.groupingBy{Named named -> named.getName()}
  def c4 = Collectors.groupingBy((Named named) -> named.getName())
}

In each case, the type inference engine should be able to work out the type of the declared variable as: Collector<Named, ?, Map<String, List<Named>>>

To do so, the parameter type Named (and return type String) must be mapped onto Function<? super T, ? extends K> of Collectors#groupingBy.

Issue Links

• is related to: GROOVY-10054 STC: Cannot infer lambda parameter types for a stream collector
• relates to: GROOVY-11259 STC loses generic information on method references