Defining an AST Transformation that returns void

Question

Here is my AST transformation

@GroovyASTTransformation(phase = CompilePhase.SEMANTIC_ANALYSIS)
public class ASTExampleTransformation implements ASTTransformation {

    public void visit(ASTNode[] astNodes, SourceUnit sourceUnit) {
        astNodes.findAll {
            node -> node instanceof ClassNode
        }.each {
            classNode ->

                println("classNode")
                def useMethodBody = new AstBuilder().buildFromCode {
                    println(">>useMethodBody")
                }


                def useMethod = new MethodNode (
                        'useMethod', ACC_PUBLIC, ClassHelper.VOID_TYPE, [] as Parameter[], [] as ClassNode[], useMethodBody[0]
                )

                classNode.addMethod(useMethod)
        }
    }



}

When I compile I get this error

[groovyc] General error during class generation: Cannot use return statement with an expression on a method that returns void

How do I build code then that returns void? Thanks.

Answer 1

I've never used the AstBuilder so I can't help you there. I would guess that the problem is that the AST builder supports Groovy style implicit returns and defaults to returning Object, or something like that?

Here's an example of building a println method call statement with the AST builder code directly. I'm honestly not 100% sure whether or not this also ends up doing a return. But I'm assuming that raw statements built with the low level AST syntax doesn't add implicit returns. There's a separate class for making return statements - ReturnStatement . So give it a try :)

Statement useMethodBody = new ExpressionStatement(
  new MethodCallExpression(
    new VariableExpression("this"),
    new ConstantExpression("println"),
    new ArgumentListExpression(
      new ConstantExpression(">>useMethodBody")
    )
  )
)

Then change useMethodBody[0] to useMethodBody . Hopefully it'll work, but I haven't actually tested this so there might be errors :)