[GROOVY-10053] STC: Wrong type inferred for lambda parameter in a generic method

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 4.0.0-beta-1, 3.0.18
• Component/s: Static Type Checker
• Environment: OpenJDK8
• Assignee: Eric Milles
• Reporter: Lyuben Atanasov
• Created: 23/Apr/21 11:29
• Updated: 26/May/23 22:42
• Resolved: 25/Apr/21 22:05

Description

Following the fix of GROOVY-10049, a new issue has appeared. Consider the following code example:

class Test {

	Set<Number> getNumbers() {
		// mock return value, needed to demonstrate the issue
		return Collections.emptySet();
	}
	
	<T extends Number> Set<T> filterNumbers(Class<T> numberType) {
		Set<T> filteredNumbers = new HashSet<>();
		getNumbers().stream()
			.filter(numberType::isInstance)
			.map(numberType::cast)
			.forEach(num -> {
				filteredNumbers.add(num);
			});
		return filteredNumbers;
	}
}

def test = new Test()'
test.filterNumbers(Integer);

Compiling with static type checking enabled produces an error:

Script_de4295e2a5171ce6c5ecd73605504d73.groovy: 14: [Static type checking] - Cannot call java.util.Set#add(T) with arguments [R] 
 @ line 14, column 5.
   				filteredNumbers.add(num);

This used to work fine before applying the fix for GROOVY-10049. Tested against https://github.com/apache/groovy/commit/e07f0112c5eff8d9c6828bd0ddb69e4b7f7cc1d6