[GROOVY-10282] STC: false positive for BiFunction and BinaryOperator with same type parameter

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 4.0.0-beta-1
• Fix Version/s: 4.0.0-beta-2, 3.0.11, 2.5.18
• Component/s: Static compilation, Static Type Checker
• Assignee: Eric Milles
• Reporter: Eric Milles
• Created: 04/Oct/21 19:43
• Updated: 19/Jul/22 22:49
• Resolved: 05/Oct/21 16:59

Description

Consider the following:

@groovy.transform.CompileStatic
String foo() {
  def integers = java.util.stream.IntStream.range(0, 10).boxed()
  integers.reduce('', (s, i) -> s + '-', String::concat)
}

reduce has the following signature in java.util.stream.Stream:

<U> U reduce(U identity, BiFunction<U, ? super T, U> accumulator, BinaryOperator<U> combiner);

The type parameter U is shared between the accumulator and combiner and should be resolved to java.lang.String. However, GenericsUtils#parameterizeSAM is producing java.lang.Integer as the return type since that is what is associated with T in this context.