Show HN: Stack Error – ergonomic error handling for Rust

github.com

19 points by garrinm 4 hours ago

Stack Error reduces the up-front cost of designing an error handling solution for your project, so that you focus on writing great libraries and applications.

Stack Error has three goals:

1. Provide ergonomics similar to anyhow.

2. Create informative error messages that facilitate debugging.

3. Provide typed data that facilitates runtime error handling.

lilyball an hour ago

If the macros only exist to get file and line information, you could do the same thing by using `#[track_caller]` functions combined with `std::panic::Location` to get that same info. For example, `stack_err!` could be replaced with

  impl StackError {
      #[track_caller]
      fn new_location(msg: impl Display) -> Self {
          let loc = std::panic::Location::caller();
          Self::new(format!("{}:{} {msg}", loc.file(), loc.line()))
      }
  }
such that you call `.map_err(StackError::new_location("data is not a list of strings"))`. A macro is nice if you need to process format strings with arguments (though someone can call `StackError::new_location(format_args!(…))` if they want), but all of your examples show static strings so it's nice to avoid the error in that case.

The use of `std::panic::Location` also means instead of baking that into a format string you could also just have that be an extra field on the error, which would let you expose accessors for it, and you can then print them in your Debug/Display impls.

Speaking of, the Display impl really should not include its source. Standard handling for errors expects that an error prints just itself with Display because it's very common to recurse through sources and print those, so if Display prints the source too then you're duplicating output. Go ahead and print it on Debug though, that's nice for errors returned from `main()`.

tevon 3 hours ago

This is awesome! Will give it a try in my next project.

How does it keep track of filename and line number in a compiled binary? I'm fairly new to rust libraries and this doesn't quite make sense to me. I know in JS you need a source-map for minification, how does this work for a compiled language?

  • fpoling 2 hours ago

    Rust provides file!, line! and column! macros that expands into a compile-time constants that the compiler embeds then into the executable. This way no source map at runtime is necessary as the relevant errors are constructed from those constants.

    Presumably StackError just uses those macros.

    But for debugging a source map is still necessary and is a part of various debug formats.

rhabarba 3 hours ago

I still prefer the Anyhow solution, but I like the approach here.

  • IshKebab an hour ago

    Isn't this strictly superior to Anyhow? What do you like more about Anyhow?