[GROOVY-10049] STC fails when calling a generic method from another generic method

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 3.0.8, 4.0.0-alpha-3, 4.0.0-beta-1
• Fix Version/s: 4.0.0-beta-2, 3.0.12
• Component/s: Static Type Checker
• Environment: OpenJDK 8
• Assignee: Eric Milles
• Reporter: Lyuben Atanasov
• Created: 21/Apr/21 11:16
• Updated: 04/Jun/22 15:14
• Resolved: 17/Sep/21 13:35

Description

The static type checker fails to properly determine the return type of a generic method when that method is called from another generic method. Here's an example:

class Test {

	<T extends Number> Set<T> generateNumbers(Class<T> numberType) {
		// mock return value, needed to demonstrate the issue
		return Collections.emptySet();
	}

	<T extends Number> void printNumbers(Class<T> numberType) {
		generateNumbers(numberType).stream()
			.filter(num -> num.doubleValue() > 0)
			.forEach(num -> println "$num");
	}
	
}

With static type checking enabled, compilation of this class fails:

Script_bbf0c00c9b2872d2a3528c2d80bbaa49.groovy: 10: [Static type checking] - Cannot find matching method java.lang.Object#doubleValue(). Please check if the declared type is correct and if the method exists.
 @ line 10, column 19.
   			.filter(num -> num.doubleValue() > 0)

If we call the generateNumbers() method with a specific class, everything works:

class Test {

	<T extends Number> Set<T> generateNumbers(Class<T> numberType) {
		return Collections.emptySet();
	}

	void printNumbers() {
		generateNumbers(Integer).stream()
			.filter(num -> num.doubleValue() > 0)
			.forEach(num -> println "$num");
	}
	
}

It looks like the static type checker does not properly take into account the generic types of the surrounding method and thus fails to determine the type of the returned value.

Issue Links

• relates to: GROOVY-10648 Compile error during static compilation (missing type derivation?)