NDLRGEN017: Validation method has wrong signature¶

Cause¶

A validation method exists but has an incorrect signature.

Rule Description¶

Validation methods must follow specific signatures to be recognized by the generator:

For methods on the options class itself:

IEnumerable<ValidationError> Validate()
IEnumerable<string> Validate()

For methods on an external validator:

IEnumerable<ValidationError> Validate(TOptions options)
IEnumerable<string> Validate(TOptions options)

If your method doesn't match one of these patterns, this error is raised.

How to Fix¶

Correct the method signature:

// ❌ Wrong - returns void instead of IEnumerable
[Options(ValidateOnStart = true)]
public class ApiOptions
{
    public string Key { get; set; } = "";

    public void Validate()  // Wrong return type!
    {
        if (string.IsNullOrEmpty(Key))
            throw new Exception("Key required");
    }
}

// ✅ Correct - returns IEnumerable<ValidationError>
[Options(ValidateOnStart = true)]
public class ApiOptions
{
    public string Key { get; set; } = "";

    public IEnumerable<ValidationError> Validate()
    {
        if (string.IsNullOrEmpty(Key))
            yield return "Key is required";
    }
}

Example¶

Code with Error¶

using NexusLabs.Needlr.Generators;

// NDLRGEN017: Method 'Validate' on type 'EmailOptions' has wrong signature
[Options(ValidateOnStart = true)]
public class EmailOptions
{
    public string SmtpHost { get; set; } = "";

    // Wrong: takes a parameter (should be parameterless for instance methods)
    public IEnumerable<string> Validate(bool strict)
    {
        if (string.IsNullOrEmpty(SmtpHost))
            yield return "SmtpHost required";
    }
}

Fixed Code¶

using NexusLabs.Needlr.Generators;

[Options(ValidateOnStart = true)]
public class EmailOptions
{
    public string SmtpHost { get; set; } = "";

    // ✅ Correct: no parameters for instance method on options class
    public IEnumerable<string> Validate()
    {
        if (string.IsNullOrEmpty(SmtpHost))
            yield return "SmtpHost required";
    }
}

Valid Signatures¶

On Options Class (instance method, no parameters)¶

public IEnumerable<ValidationError> Validate()
public IEnumerable<string> Validate()

On External Validator (takes options as parameter)¶

// Instance method
public IEnumerable<ValidationError> Validate(TOptions options)
public IEnumerable<string> Validate(TOptions options)

// Static method
public static IEnumerable<ValidationError> Validate(TOptions options)
public static IEnumerable<string> Validate(TOptions options)

Common Mistakes¶

Wrong Signature	Problem	Correct Signature
`void Validate()`	Wrong return type	`IEnumerable<ValidationError> Validate()`
`bool Validate()`	Wrong return type	`IEnumerable<string> Validate()`
`List<string> Validate()`	Must be IEnumerable	`IEnumerable<string> Validate()`
`IEnumerable<ValidationError> Validate(bool flag)`	Extra parameter	`IEnumerable<ValidationError> Validate()`