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XPC3003: Image registration without method reference

Severity

Warning

Description

This rule reports when WithPreImage() or WithPostImage() is used with a lambda invocation expression (e.g., s => s.HandleUpdate()) instead of a method reference expression (e.g., nameof(IService.HandleUpdate)). When images are registered with the modern API, the source generator needs to know the method name to generate type-safe wrapper classes and validate the handler signature. Method invocation syntax prevents the generator from extracting this information.

Note: This rule only applies to the modern WithPreImage()/WithPostImage() API. For the legacy AddImage() API, see XPC3002.

❌ Example of violation

public class AccountPlugin : Plugin
{
    public AccountPlugin()
    {
        // XPC3003: WithPreImage/WithPostImage requires method reference syntax
        RegisterStep<Account, IAccountService>(
            EventOperation.Update,
            ExecutionStage.PostOperation,
            s => s.HandleUpdate())  // Method invocation with parentheses - BAD
            .WithPreImage(x => x.Name);
    }
}

public interface IAccountService
{
    void HandleUpdate(PreImage preImage);
}

✅ How to fix

Use nameof() to reference the handler method when registering images:

public class AccountPlugin : Plugin
{
    public AccountPlugin()
    {
        // Correct: Use nameof() for method reference when images are registered
        RegisterStep<Account, IAccountService>(
            EventOperation.Update,
            ExecutionStage.PostOperation,
            nameof(IAccountService.HandleUpdate))  // nameof() for compile-time safety
            .WithPreImage(x => x.Name);
    }
}

public interface IAccountService
{
    void HandleUpdate(PreImage preImage);
}

When to use each syntax

Registration Type Recommended Syntax Example
With images nameof() nameof(IService.Method)
Without images Lambda invocation s => s.Method()

Why this matters

  1. Type-safe wrapper generation: The source generator creates strongly-typed PreImage and PostImage wrapper classes based on the registered attributes. It needs to know the handler method name to generate and inject these wrappers correctly.

  2. Signature validation: When using nameof(), the source generator can validate that the handler method's signature matches the registered images (XPC4002). With lambda invocation syntax, this validation cannot be performed.

  3. Runtime behavior: Without the method reference, the source generator cannot generate the wrapper classes. This means your handler method will not receive the type-safe image wrappers, and you'll need to manually extract images from the execution context.

  4. Consistency: Using nameof() when images are registered and lambda invocation when no images are needed creates a clear pattern that indicates what each registration expects.

See also