#[source]

• to identify underlying cause
• field marked #[source] or is named source

Examples

Source

#[derive(Error, Debug)]
pub struct MyError {
    msg: String,
    #[source]  // optional if field name is `source`
    source: anyhow::Error,
}

Caveats

• source must implement Error or Deref<Target = dyn Error>

References

• thiserror