Derive Macro ModError 

#[derive(ModError)]
{
    // Attributes available to this derive:
    #[error_prefix]
    #[error_display]
    #[error_kind]
    #[error_caption]
    #[error_retryable]
    #[error_http_status]
    #[error_exit_code]
    #[error_fatal]
}

Derive macro for ModError

This macro automatically implements the ForgeError trait and common error handling functionality for a struct or enum, allowing for “lazy mode” error creation with minimal boilerplate.

Example

When the macro is used in your application where error-forge is a dependency:

use error_forge::ModError;

#[derive(Debug, ModError)]
#[error_prefix("Database")]
pub enum DbError {
    #[error_display("Connection to {0} failed")]
    ConnectionFailed(String),

    #[error_display("Query execution failed: {reason}")]
    QueryFailed { reason: String },

    #[error_display("Transaction error")]
    #[error_http_status(400)]
    TransactionError,
}

#[error_display("...")] is optional; without it a variant displays as its name. The string is a format! string and may reference any subset of the variant’s fields: by name for struct-like variants (a raw identifier such as r#type is written {type}), by position ({0}, {}) for tuple variants. Fields it does not mention are ignored, {{ and }} produce literal braces, and a width or precision given where the error is formatted ({:>20}) pads or truncates the whole message.

Attributes

On the enum (or struct):

• #[error_prefix("...")]: caption prefix, giving "<prefix>: Error".

On each enum variant:

• #[error_display("...")], #[error_kind("...")], #[error_caption("...")]: string literals.
• #[error_retryable], #[error_fatal]: flags. A bare flag means true; an explicit value (#[error_retryable(false)] or #[error_retryable = false]) is honoured.
• #[error_http_status(404)]: an integer that fits in u16.
• #[error_exit_code(2)]: an integer that fits in i32.

Each attribute accepts both the list form (#[name(value)]) and the name-value form (#[name = value]). A value of the wrong type or out of range is a compile error.

Structs

On a struct only #[error_prefix] is read. The struct displays as "<prefix>: Error", its kind() is the struct name, and the other metadata methods use the ForgeError defaults. The variant attributes listed above (#[error_display], #[error_retryable], and so on) are currently ignored when placed on a struct.

Note: This is a procedural macro that is re-exported by the error-forge crate. When using in your application, import it from the main crate with use error_forge::ModError;.