Function error_annotation::annotate

pub fn annotate<S, F, I>(
    label: &'static str, 
    mkinfo: F
) -> impl FnOnce(S) -> ErrorAnnotation<S, I> where
    F: FnOnce() -> I, 

Capture diagnostic information in a closure that extends a source error type into a wrapping ErrorAnnotation.

annotate captures a label and a diagnostic info construction closure, mkinfo, returning a closure that creates an ErrorAnnotation given a source error of type S. This API design makes it ergonomic to use as the parameter to Result::map_err to transform a source error by extending it with diagnostic information.

mkinfo is a closure which allows deferring the construction of the diagnostic info until the error case is encountered, similar to the design of Option::ok_or_else.

Example

use std::path::Path;
use std::fs::Metadata;
use error_annotation::{ErrorAnnotation, annotate};

type IoErrorWithPath<'a> = ErrorAnnotation<std::io::Error, std::path::Display<'a>>;

fn metadata(p: &Path) -> Result<Metadata, IoErrorWithPath> {
  std::fs::metadata(p).map_err(annotate("path", || p.display()))
}