LA0148: Aspect Role Dependency Has No Role


Severity	Error
Reported by	PostSharp
Message	`Invalid value for AspectRoleDependencyAttribute: the "role" parameter value cannot be null or empty.`

Cause

The AspectRoleDependencyAttribute custom attribute declares a dependency between the aspect that it is applied to and the aspects or advices of a role, such as ordering them or forbidding them on the same target. The dependency matches the aspects and advices that are enrolled in the role with ProvideAspectRoleAttribute, by its name. A dependency without a name matches nothing, so PostSharp reports LA0148 when the role argument is null or an empty string.

PostSharp reports the message without a location, and the message does not name the aspect. Look for an AspectRoleDependencyAttribute whose role is empty, or comes from a constant or an expression that is empty, on the aspects that the project uses.

In the following example, the [Log] aspect declares a dependency with an empty role.

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using System;
using PostSharp.Aspects;
using PostSharp.Aspects.Dependencies;
using PostSharp.Serialization;

namespace Errors.LA0148_Error;

[PSerializable]
[ProvideAspectRole( StandardRoles.Caching )]
public class CacheAttribute : OnMethodBoundaryAspect
{
    public override void OnEntry( MethodExecutionArgs args ) => Console.WriteLine( "Looking up the cache." );
}

[PSerializable]
// The role of the dependency is empty.
[AspectRoleDependency( AspectDependencyAction.Order, AspectDependencyPosition.Before, "" )]
public class LogAttribute : OnMethodBoundaryAspect
{
    public override void OnEntry( MethodExecutionArgs args ) => Console.WriteLine( $"Entering {args.Method.Name}." );
}

public class ProductCatalog
{
    [Log]
    [Cache]
    public decimal GetPrice( string product ) => 12.5m;
}

public static class Program
{
    public static void Main()
    {
        Console.WriteLine( new ProductCatalog().GetPrice( "Book" ) );
    }
}

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error LA0148: Invalid value for AspectRoleDependencyAttribute: the "role" parameter value cannot be null or empty.

Resolution

Pass the name of a role to the attribute, preferably a constant of StandardRoles, or the role that the other aspect declares with ProvideAspectRoleAttribute. If the aspect does not depend on any role, remove the attribute.

In the following example, the [Log] aspect runs before the aspects of the caching role.

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using System;
using PostSharp.Aspects;
using PostSharp.Aspects.Dependencies;
using PostSharp.Serialization;

namespace Errors.LA0148_Fixed;

[PSerializable]
[ProvideAspectRole( StandardRoles.Caching )]
public class CacheAttribute : OnMethodBoundaryAspect
{
    public override void OnEntry( MethodExecutionArgs args ) => Console.WriteLine( "Looking up the cache." );
}

[PSerializable]
// The dependency names the role of the caching aspect.
[AspectRoleDependency( AspectDependencyAction.Order, AspectDependencyPosition.Before, StandardRoles.Caching )]
public class LogAttribute : OnMethodBoundaryAspect
{
    public override void OnEntry( MethodExecutionArgs args ) => Console.WriteLine( $"Entering {args.Method.Name}." );
}

public class ProductCatalog
{
    [Log]
    [Cache]
    public decimal GetPrice( string product ) => 12.5m;
}

public static class Program
{
    public static void Main()
    {
        Console.WriteLine( new ProductCatalog().GetPrice( "Book" ) );
    }
}

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Entering GetPrice.
Looking up the cache.
12.5

Cause

Resolution

See Also