Question

I want to write a rule that will fail if an object allocation is made within any method called by a method marked with a particular attribute.

I’ve got this working so far, by iterating up all methods calling my method to check using CallGraph.CallersFor(), to see if any of those parent methods have the attribute.

This works for checking parent methods within the same assembly as the method to be checked, however reading online, it appears that at one time CallGraph.CallersFor() did look at all assemblies, however now it does not.

Question: Is there a way of getting a list of methods that call a given method, including those in a different assembly?

Alternative Answer: If the above is not possible, how do i loop through every method that is called by a given method, including those in a different assembly.

---

Example:

-----In Assembly A

public class ClassA
{
    public MethodA()
    {
        MethodB();
    }

    public MethodB()
    {
        object o = new object(); // Allocation i want to break the rule
        // Currently my rule walks up the call tree,
        // checking for a calling method with the NoAllocationsAllowed attribute.
        // Problem is, because of the different assemblies,
        // it can't go from ClassA.MethodA to ClassB.MethodB.
    }
}


----In Assembly B

public var ClassAInstance = new ClassA();

public class ClassB
{
    [NoAllocationsAllowed] // Attribute that kicks off the rule-checking.
    public MethodA()
    {
        MethodB();
    }

    public MethodB()
    {
        ClassAInstance.MethodA();
    }
}

I don’t really mind where the rule reports the error, at this stage getting the error is enough.

Answer 1

I got round this issue by adding all referenced dlls in my FxCop project, and using the code below, which builds a call tree manually (it also adds calls for derived classes to work round another problem i encountered, here.

public class CallGraphBuilder : BinaryReadOnlyVisitor
{
    public Dictionary<TypeNode, List<TypeNode>> ChildTypes;

    public Dictionary<Method, List<Method>> CallersOfMethod;

    private Method _CurrentMethod;

    public CallGraphBuilder()
        : base()
    {
        CallersOfMethod = new Dictionary<Method, List<Method>>();
        ChildTypes = new Dictionary<TypeNode, List<TypeNode>>();
    }

    public override void VisitMethod(Method method)
    {
        _CurrentMethod = method;

        base.VisitMethod(method);
    }

    public void CreateTypesTree(AssemblyNode Assy)
    {
        foreach (var Type in Assy.Types)
        {
            if (Type.FullName != "System.Object")
            {
                TypeNode BaseType = Type.BaseType;

                if (BaseType != null && BaseType.FullName != "System.Object")
                {
                    if (!ChildTypes.ContainsKey(BaseType))
                        ChildTypes.Add(BaseType, new List<TypeNode>());

                    if (!ChildTypes[BaseType].Contains(Type))
                        ChildTypes[BaseType].Add(Type);
                }
            }
        }
    }

    public override void VisitMethodCall(MethodCall call)
    {
        Method CalledMethod = (call.Callee as MemberBinding).BoundMember as Method;

        AddCallerOfMethod(CalledMethod, _CurrentMethod);

        Queue<Method> MethodsToCheck = new Queue<Method>();

        MethodsToCheck.Enqueue(CalledMethod);

        while (MethodsToCheck.Count != 0)
        {
            Method CurrentMethod = MethodsToCheck.Dequeue();

            if (ChildTypes.ContainsKey(CurrentMethod.DeclaringType))
            {
                foreach (var DerivedType in ChildTypes[CurrentMethod.DeclaringType])
                {
                    var DerivedCalledMethod = DerivedType.Members.OfType<Method>().Where(M => MethodHidesMethod(M, CurrentMethod)).SingleOrDefault();

                    if (DerivedCalledMethod != null)
                    {
                        AddCallerOfMethod(DerivedCalledMethod, CurrentMethod);

                        MethodsToCheck.Enqueue(DerivedCalledMethod);
                    }
                }
            }
        }

        base.VisitMethodCall(call);
    }

    private void AddCallerOfMethod(Method CalledMethod, Method CallingMethod)
    {
        if (!CallersOfMethod.ContainsKey(CalledMethod))
            CallersOfMethod.Add(CalledMethod, new List<Method>());

        if (!CallersOfMethod[CalledMethod].Contains(CallingMethod))
            CallersOfMethod[CalledMethod].Add(CallingMethod);
    }

    private bool MethodHidesMethod(Method ChildMethod, Method BaseMethod)
    {
        while (ChildMethod != null)
        {
            if (ChildMethod == BaseMethod)
                return true;

            ChildMethod = ChildMethod.OverriddenMethod ?? ChildMethod.HiddenMethod;
        }

        return false;
    }
}