Modify method using AST Transformation in Groovy - groovy

Question

The original question was deleted before I could follow up with a further answer it, so I'm reposting the question with the answer to follow:
I am unable to modify my method using AST Transformation as I cannot figure out how to execute previous method statements after my modification. I extract the statements from the method, save it in some temporary variable, but later, after my modification, when I try to execute it I get MissingPropertyException: No such property: code for class: Calculator as like I am trying to use a property from my class and not the previous code block from my method. Any ideas what am I doing wrong?
//annotation
#Retention(RetentionPolicy.SOURCE)
#Target([ElementType.TYPE])
#GroovyASTTransformationClass("CreatedAtTransformation")
public #interface CreatedAt {
String name() default "";
}
//AST Transformation
#GroovyASTTransformation(phase = SEMANTIC_ANALYSIS)
public class CreatedAtTransformation implements ASTTransformation {
public void visit(ASTNode[] astNodes, SourceUnit source) {
//private final long field creation
ClassNode myClass = (ClassNode) astNodes[1]
ClassNode longClass = new ClassNode(Long.class)
FieldNode field = new FieldNode("timeOfInstantiation", FieldNode.ACC_PRIVATE | FieldNode.ACC_FINAL, longClass, myClass, new ConstantExpression(System.currentTimeMillis()))
myClass.addField(field)
//statement
AstBuilder ab = new AstBuilder()
List<ASTNode> statement = ab.buildFromCode {
timeOfInstantiation
}
//value of the annotation expression(name of the method)
def annotationExpression = astNodes[0].members.name
String annotationValueString = annotationExpression.value
//public final method creation
myClass.addMethod(annotationValueString, Opcodes.ACC_PUBLIC | Opcodes.ACC_FINAL, ClassHelper.Long_TYPE,[] as Parameter[], [] as ClassNode[], statement[0])
//modification of method "add"
def addMethods = myClass.getMethods("add")
for(m in addMethods){
def code = m.getCode().statements
//statement
AstBuilder abc = new AstBuilder()
List<ASTNode> statement1 = abc.buildFromCode {
timeOfInstantiation = System.currentTimeMillis()
for(c in code){
c.expression
}
}
m.setCode(statement1[0])
}
//modification of method "subtract"
def subtractMethods = myClass.getMethods("subtract")
for(m in subtractMethods){
def code = m.getCode().statements
//statement
AstBuilder abc = new AstBuilder()
List<ASTNode> statement1 = abc.buildFromCode {
timeOfInstantiation = System.currentTimeMillis()
for(c in code){
c.expression
}
}
m.setCode(statement1[0])
}
}
}
//class
final calculator = new GroovyShell(this.class.getClassLoader()).evaluate('''
#CreatedAt(name = "timestamp")
class Calculator {
int sum = 0
def add(int value) {
int v = sum + value
sum = v
}
def subtract(int value) {
sum -= value
}
}
new Calculator()
''')
//test
assert System.currentTimeMillis() >= calculator.timestamp()
assert calculator.timestamp() == calculator.timestamp()
def oldTimeStamp = calculator.timestamp()
sleep(1000)
calculator.add(10)
assert oldTimeStamp < calculator.timestamp()
assert calculator.timestamp() == calculator.timestamp()
oldTimeStamp = calculator.timestamp()
sleep(1000)
calculator.subtract(1)
assert oldTimeStamp < calculator.timestamp()
assert calculator.timestamp() == calculator.timestamp()
println 'well done'
There is more code than is actually needed for the question. Important part are those modifications of methods. Thanks in advance.
From my perspective I don't know if the code from the AST is actually useful or just to get and example working, to learn AST Transforms...

Answer 1

So my original answer was:
It can be hard to get help when it comes to AST transforms. While it is a guess I'm thinking it might have to do with variable scope. There is a VariableScopeVisitor that is run early in the AST process, setting the scoping of variables, however from the description of your AST you are adding code that you want to access later. So you may have to run the VariableScopeVisitor again, to fix it so that the existing code has access to your injected code.
I did an intro AST talk at GR8Conf.US this year, which has a lot of resources:
https://docs.google.com/presentation/d/1D4B0YQd0_0HYxK2FOt3xILM9XIymh-G-jh1TbQldbVA/edit?usp=sharing
I would take a look at this article that talks about variable scope:
However the real answer is that
AST Transforms can be difficult, and using the AstBuilder while it can be convience can introduce issues, so I often use the API directly. Once I learn Macros and Macro Methods, new in Groovy 2.5 I might not have to use the API as much, but until then I rewrote part of the code using the API like this:
//modification of method "add"
def addMethods = myClass.getMethods("add")
for(m in addMethods){
def code = m.getCode().statements
//statement
//AstBuilder abc = new AstBuilder()
Statement s1 = new ExpressionStatement(
new BinaryExpression(
new VariableExpression('timeOfInstantiation'),
Token.newSymbol(org.codehaus.groovy.syntax.Types.EQUAL,0,0),
new MethodCallExpression(
new ClassExpression(new ClassNode(java.lang.System)),
'currentTimeMillis',
ArgumentListExpression.EMPTY_ARGUMENTS
)
)
)
// List<ASTNode> statement1 = abc.buildFromString('timeOfInstantiation = System.currentTimeMillis()')
// List<ASTNode> statement1 = abc.buildFromCode {
// timeOfInstantiation = System.currentTimeMillis()
// for(c in code){
// c.expression
// }
// }
code.add(0,s1)
//m.setCode(statement1[0])
}
This code can be cleaned up a bit, but it should work. I also had to change the timeOfInstantiation to be private, instead of final, so that the assignment code would work like this:
FieldNode field = new FieldNode("timeOfInstantiation", FieldNode.ACC_PRIVATE, longClass, myClass, new ConstantExpression(System.currentTimeMillis()))
I would also look into the test application reference in my presentation, as it will allow for debugging AST Transforms and using the Groovy Console to see what the transforms are doing.