When a shape is annotated with @error, the code generator implements the std::error::Error and std::fmt::Display trait for that error structure. However, if this error structure contains a member field that references another structure, the code generator doesn't implement Display for the referenced structure, resulting in compilation errors.

For example, the following model generates uncompilable code:

@error("client")
structure ErrorInInput {
    message: ErrorMessage
}

structure ErrorMessage {
    @required
    statusCode: String
    @required
    errorMessage: String
    requestId: String
}

The root cause is that when a shape is annotated with @error, the code generator implements std::error::Error for that type:

impl std::error::Error for ErrorInInput {}

This implementation requires that the type also implements the Display trait. While the code generator correctly implements Display for ErrorInInput, it attempts to forward the display implementation to the message field. However, since ErrorMessage structure doesn't have a Display implementation, compilation fails.

Generated Code

pub struct ErrorInInput {
    #[allow(missing_docs)] // documentation missing in model
    pub message: ::std::option::Option<crate::model::ErrorMessage>,
}

impl ::std::fmt::Display for ErrorInInput {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        ::std::write!(f, "ErrorInInput")?;
        if let ::std::option::Option::Some(inner_2) = &self.message {
            {
                ::std::write!(f, ": {}", inner_2)?;
            }
        }
        Ok(())
    }
}
impl ::std::error::Error for ErrorInInput {}