LA0227: No Argument of the Bound Type


Severity	Error
Reported by	PostSharp
Message	`The parameter "<Parameter>" of the advice "<Advice>" is bound by [Argument] to an argument of its type, but "<TargetMethod>" has no parameter whose type can be assigned to "<ParameterType>" without conversion, except boxing, or has exactly this type when the advice parameter is passed by reference.`

Cause

The constructor of ArgumentAttribute without parameters binds a parameter of an advice to the argument of the target method whose type matches the type of the advice parameter. An argument matches when:

the advice parameter is passed by value, and the type of the argument can be assigned to <ParameterType> without conversion, except boxing. For instance, an object parameter matches an argument of any type, but a long parameter does not match an int argument;
the advice parameter is passed by reference, with in, ref or out, and the argument has exactly its type;
the advice parameter is of a type parameter of the advice, which matches any argument.

When no argument of a target method matches, PostSharp reports LA0227 on that method. When several arguments match, PostSharp reports LA0228, unless the AmbiguityResolution property selects one of them. When the advice uses a pointcut that skips the targets whose signature does not match, such as MatchPointcut, PostSharp skips the target instead of reporting the error.

In the following example, the [CheckCancellation] aspect receives the CancellationToken argument of the target method, but BuildReport has none.

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

namespace Errors.LA0227_Error;

[PSerializable]
public sealed class CheckCancellationAttribute : MethodLevelAspect
{
    [OnMethodEntryAdvice]
    public void OnEntry( [Argument] CancellationToken cancellationToken )
    {
        cancellationToken.ThrowIfCancellationRequested();
    }
}

public class ReportService
{
    // The method has no parameter of type CancellationToken.
    [CheckCancellation]
    public string BuildReport( string title ) => $"Report: {title}";
}

public static class Program
{
    public static void Main()
    {
        Console.WriteLine( new ReportService().BuildReport( "Sales" ) );
    }
}

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error LA0227: LA0227_Error.cs(23,19): The parameter "cancellationToken" of the advice "Errors.LA0227_Error.CheckCancellationAttribute.OnEntry(System.Threading.CancellationToken)" is bound by [Argument] to an argument of its type, but "Errors.LA0227_Error.ReportService.BuildReport(System.String)" has no parameter whose type can be assigned to "System.Threading.CancellationToken" without conversion, except boxing, or has exactly this type when the advice parameter is passed by reference.

Resolution

Add a parameter of the expected type to the target method.
Change the type of the advice parameter to a type that the argument can be assigned to, or pass the parameter by value to accept boxing.
Otherwise, apply the aspect only to methods that have an argument of this type, or use MatchPointcut in a type-level aspect to skip the other methods.

In the following example, BuildReport receives the CancellationToken that the aspect checks.

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

namespace Errors.LA0227_Fixed;

[PSerializable]
public sealed class CheckCancellationAttribute : MethodLevelAspect
{
    [OnMethodEntryAdvice]
    public void OnEntry( [Argument] CancellationToken cancellationToken )
    {
        cancellationToken.ThrowIfCancellationRequested();
    }
}

public class ReportService
{
    // The method receives the CancellationToken that the aspect checks.
    [CheckCancellation]
    public string BuildReport( string title, CancellationToken cancellationToken ) => $"Report: {title}";
}

public static class Program
{
    public static void Main()
    {
        ReportService service = new();
        Console.WriteLine( service.BuildReport( "Sales", CancellationToken.None ) );

        try
        {
            service.BuildReport( "Stock", new CancellationToken( true ) );
        }
        catch ( OperationCanceledException )
        {
            Console.WriteLine( "Stock: canceled" );
        }
    }
}

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Report: Sales
Stock: canceled

Cause

Resolution

See Also