Trait Emit

Source

pub trait Emit {
    // Required method
    fn emit(&self) -> DiagnosticEmitted;
}

Expand description

Trait for types that can emit themselves as diagnostics.

Even in the error handling framework set up in formally, in some cases the best design for a function is to return a classic Result<T, E> for some specific error type E and postpone the emission of diagnostics. In this case one can embedd in the error type all the necessary information to generate the diagnostics later, and implement Emit for the error type.

Then, the error type can be used as any other, but in addition, DiagnosticEmitted implements From<E> for any E that implement Emit, and the conversion emits the diagnostics. This means that one can very conveniently apply to E the ? operator in a function returning Result<T, DiagnosticEmitted>, if and when one desires to finally emit the diagnostics.

A suggested way to declare error types is using the thiserror crate. In this case, to inherit a sensible implementation of Emit for common error types one can implement Diagnosable instead. For an example see formally::smt::backends::BackendError type, and the documentation of Diagnosable.