LA0049: Advice Without Pointcut Cannot Apply to the Target of the Aspect


Severity	Error
Reported by	PostSharp
Message	`The advice "<Advice>" is in a group without pointcut, so it applies to the target of the aspect, "<Target>", but it cannot be applied to this kind of declaration. Add a pointcut to an advice of the group, for instance [MulticastPointcut].`

Cause

A pointcut selects the declarations that a group of advices transforms. PostSharp puts an advice without pointcut in a group of its class: the group of an advice that has a pointcut, when there is one, or else a group without pointcut, which applies to the target of the aspect itself. A group without pointcut works only when its advices accept this kind of declaration. When they do not, PostSharp reports LA0049. The typical case is a method advice, such as an OnMethodEntryAdvice, in a TypeLevelAspect: the target of the aspect is a type, and the advice can only transform methods.

<Advice> is one advice of the group, and the message is reported on it: the advice that sets a property of the group, or else the first advice of the group. <Target> is the declaration to which the aspect is applied.

In the following example, the [Trace] aspect is applied to the OrderService class, and its entry advice has no pointcut.

Full screen

using System;
using PostSharp.Aspects;
using PostSharp.Aspects.Advices;
using PostSharp.Serialization;

namespace Errors.LA0049_Error;

[PSerializable]
public class TraceAttribute : TypeLevelAspect
{
    // The advice has no pointcut, so it applies to the class, but a method entry advice can only apply to methods.
    [OnMethodEntryAdvice]
    public void OnEntry( MethodExecutionArgs args )
    {
        Console.WriteLine( $"Entering {args.Method.Name}" );
    }
}

[Trace]
public class OrderService
{
    public void PlaceOrder( string product )
    {
        Console.WriteLine( $"Order placed for {product}" );
    }
}

public static class Program
{
    public static void Main()
    {
        new OrderService().PlaceOrder( "Coffee" );
    }
}

Full screen

error LA0049: LA0049_Error.cs(13,17): The advice "Errors.LA0049_Error.TraceAttribute.OnEntry(PostSharp.Aspects.MethodExecutionArgs)" is in a group without pointcut, so it applies to the target of the aspect, "Errors.LA0049_Error.OrderService", but it cannot be applied to this kind of declaration. Add a pointcut to an advice of the group, for instance [MulticastPointcut].

Resolution

Add a pointcut that selects the declarations that the advices accept, for instance a MulticastPointcut that selects the methods of the target type, or a MethodPointcut that selects them with code. A group has one pointcut, which can be on any of its advices, and the other advices of the group apply to the same declarations.
Or make the aspect a MethodLevelAspect and apply it to the methods, when the advices should transform only the target of the aspect.

In the following example, a MulticastPointcut selects the public methods of OrderService.

Full screen

using System;
using PostSharp.Aspects;
using PostSharp.Aspects.Advices;
using PostSharp.Extensibility;
using PostSharp.Serialization;

namespace Errors.LA0049_Fixed;

[PSerializable]
public class TraceAttribute : TypeLevelAspect
{
    // The pointcut selects the public methods of the class.
    [OnMethodEntryAdvice, MulticastPointcut( Targets = MulticastTargets.Method, Attributes = MulticastAttributes.Public )]
    public void OnEntry( MethodExecutionArgs args )
    {
        Console.WriteLine( $"Entering {args.Method.Name}" );
    }
}

[Trace]
public class OrderService
{
    public void PlaceOrder( string product )
    {
        Console.WriteLine( $"Order placed for {product}" );
    }
}

public static class Program
{
    public static void Main()
    {
        new OrderService().PlaceOrder( "Coffee" );
    }
}

Full screen

Entering PlaceOrder
Order placed for Coffee

Cause

Resolution

See Also