Derive Macro ProblemDetails 

#[derive(ProblemDetails)]
{
    // Attributes available to this derive:
    #[status_code]
    #[problem_type]
    #[title]
    #[detail]
    #[instance]
}

ProblemDetails derive macro

Derives the From<T> for ProblemDetails trait for error enums. This macro automatically generates implementations for converting error variants to RFC 7807 Problem Details responses.

Each variant must have a #[status_code(code)] attribute.

Supported Attributes

• #[status_code(code)] - Required: HTTP status code (e.g., 400, 404, 500)
• #[problem_type("uri")] - Optional: Custom problem type URI
• #[title("title")] - Optional: Custom problem title
• #[detail("detail")] - Optional: Custom problem detail message
• #[instance("uri")] - Optional: Problem instance URI

Title Compatibility

The title field can be automatically derived from the #[error("...")] attribute if no explicit #[title("...")] is provided. This provides compatibility with thiserror::Error and reduces duplication.

Basic Example

use spring_web::ProblemDetails;

#[derive(ProblemDetails)]
pub enum ApiError {
    #[status_code(400)]
    ValidationError,
    #[status_code(404)]
    NotFound,
    #[status_code(500)]
    InternalError,
}

Advanced Example with Custom Attributes

#[derive(ProblemDetails)]
pub enum ApiError {
    // Explicit title
    #[status_code(400)]
    #[title("Input Validation Failed")]
    #[detail("The provided input data is invalid")]
    #[error("Validation error")]
    ValidationError,
     
    // Title derived from error attribute
    #[status_code(422)]
    #[detail("Request data failed validation")]
    #[error("Validation Failed")]  // This becomes the title
    ValidationFailed,
     
    // Full customization
    #[status_code(404)]
    #[problem_type("https://api.example.com/problems/not-found")]
    #[title("Resource Not Found")]
    #[detail("The requested resource could not be found")]
    #[instance("/users/123")]
    #[error("Not found")]
    NotFound,
}

This will automatically implement:

• From<T> for ProblemDetails trait for converting to Problem Details responses
• IntoResponse trait for direct use in Axum handlers
• OpenAPI integration for documentation generation