[GROOVY-9977] @CompileStatic does not work when a class field has a lambda initializer

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 3.0.7, 4.0.0-alpha-2
• Fix Version/s: 3.0.8, 4.0.0-alpha-3
• Component/s: Static compilation, Static Type Checker
• Environment: OpenJDK8
• Assignee: Eric Milles
• Reporter: Lyuben Atanasov
• Created: 10/Mar/21 18:24
• Updated: 02/May/21 09:16
• Resolved: 21/Mar/21 18:31

Description

Using @CompileStatic when a field is initialized with a lambda:

class LambdaAssignedToField
{
	private Comparator<Integer> myComparator = (int1, int2) -> Integer.compare(int1, int2);
}

causes compilation errors:

Exception in thread "main" org.codehaus.groovy.control.MultipleCompilationErrorsException: startup failed:
Script_28800dd8352617dbb4fe2e1957614875.groovy: 3: [Static type checking] - Cannot find matching method java.lang.Integer#compare(java.lang.Object, java.lang.Object). Please check if the declared type is correct and if the method exists.
 @ line 3, column 61.
   yComparator = (int1, int2) -> Integer.co
                                 ^

Script_28800dd8352617dbb4fe2e1957614875.groovy: 3: [Static type checking] - Cannot assign value of type groovy.lang.Closure <java.lang.Object> to variable of type java.util.Comparator <Integer>
 @ line 3, column 45.
   rator<Integer> myComparator = (int1, int

The same code, used in the context of a method, works fine:

class LambdaAssignedToVariable
{
	public void test()
	{
		Comparator<Integer> myComparator = (int1, int2) -> Integer.compare(int1, int2);
	}
}

In order to make the first example compile, I have to manually specify the types of the lambda parameters and also cast it to the correct type:

class LambdaAssignedToFieldCast
{
	private Comparator<Integer> myComparator = (Comparator<Integer>) (Integer int1, Integer int2) -> Integer.compare(int1, int2);
}

The issue seems to exist since Groovy 3.0.0.