notes/pl/groovy/groovy-ast.txt

package devoxx.demo

import org.codehaus.groovy.transform.GroovyASTTransformationClass

import java.lang.annotation.ElementType
import java.lang.annotation.Retention
import java.lang.annotation.RetentionPolicy
import java.lang.annotation.Target

@Retention(RetentionPolicy.SOURCE)
@Target(ElementType.TYPE)
@GroovyASTTransformationClass("devoxx.demo.MagicNumberTransformation")
@interface MagicNumber {
}


@MagicNumber
class Foo {
}

class MagicNumberTransformationSpec extends Specification {
    void 'test MagicNumber annotation'() {
        given:
            def foo = new Foo()
        expect:
            42 == foo.magicNumber
    }
}

package devoxx.demo

import org.codehaus.groovy.ast.ASTNode
import org.codehaus.groovy.ast.ClassNode
import org.codehaus.groovy.ast.MethodNode
import org.codehaus.groovy.ast.Parameter
import org.codehaus.groovy.ast.expr.ConstantExpression
import org.codehaus.groovy.ast.stmt.ReturnStatement
import org.codehaus.groovy.control.SourceUnit
import org.codehaus.groovy.transform.ASTTransformation
import org.codehaus.groovy.transform.GroovyASTTransformation

@GroovyASTTransformation
class MagicNumberTransformation implements ASTTransformation {
    @Override
    void visit(ASTNode[] nodes, SourceUnit source) {
        ClassNode classNode = nodes[1] // 0 - annotation node, 1 - Foo-class-node

        def code = new ReturnStatement(
            new ConstantExpression(42)
        )

        def mn = new MethodNode("getMagicNumber", Modifier.PUBLIC
            , ClassHelper.make(Integer) // return-type
            , new Parameter[0]          // no-params
            , null                      // don't throw any ex
            code
        )

        classNode.addMethod(mn)
    }
}

OOB AST transformations:
@Delegate
@Immutable
@PackageScope
@Singleton

class SomeThing {
    @Delegate
    Map props = [:]
    // The @Delegate will add all the Map-methods to SomeThing and delegate them to props
    // But, of cause, we can override a generated behaviour
}

************************

@GroovyASTTransformation
class MagicNumberTransformation implements ASTTransformation {
    @Override
    void visit(ASTNode[] nodes, SourceUnit source) {
        ClassNode classNode = nodes[1] // 0 - annotation node, 1 - Foo-class-node

        def astNodes = new AstBuilder().buildFromSpec(
            method('getMagicNumber', Modifier.PUBLIC, Integer) {
                parameters {}
                exceptions {}
                block {
                    returnStatement {
                        return 42
                    }
                }
            }
        )

        def method = astNodes[0]
        classNode.addMethod(method)
    }
}