Use span in error make

[KAAtheWiseGit]

Related problem

Currently error make takes in a record, which has start and end fields. I think this is somewhat unergonomic, as in majority of times some existing span is passed to it. This would get rid of currently necessary patter of creating a temporary span variable. And if a custom span has to be made (a rarer case, IMO), it can still be created manually, just with one more level of nesting.

Describe the solution you'd like

Replace label: {text: "...", start: ..., end: ...} with label: {text: "...", span: ...}.

Example

Currently (an example from error make docs):

    def foo [x] {
        let span = (metadata $x).span;
        error make {
            msg: "this is fishy"
            label: {
                text: "fish right here"
                start: $span.start
                end: $span.end
            }
        }
    }

With the proposed change:

    def foo [x] {
        error make {
            msg: "this is fishy"
            label: {
                text: "fish right here"
                span: (metadata $x).span
            }
        }
    }

[fdncred]

I wonder if we can use both? like if we detect a "span:" key, look for a span and if we see a "start:" and "end:" use the individual ones. I say that we probably want to keep start/end because sometimes you have to tweak the span's start or end. That probably doesn't happen that often but it may happen.

[KAAtheWiseGit]

@fdncred in theory, there are two ways to ways to tweak the ends with this proposal:

mut span = (metadata $x).span
span.end += 10
...

error make {
    label: {
        span: {
            start: 10
            end: 20
        }
    }
}

I didn't think about the idea to mix them, though, and I like it. One thing which I worry about is the error message when the two get mixed. If someone puts both span and start/end, what should the error say?

[fdncred]

It should be an error if someone puts both span and start/end stating that it's disallowed and to choose either span or start/end. One other benefit to doing it this way is that it keeps us from having a breaking-change.

[amtoine]

i think this would be quite cool to have 🙏

[fdncred]

Related/Unrelated, I was reminded again today that error make doesn't allow the addition of the help: line. It would be nice to have an optional help: key in the creation of error make.

Example

❯ ls | into list -adfa
Error: nu::parser::unknown_flag

  × The `into list` command doesn't have flag `-a`.
   ╭─[entry #44:1:1]
 1 │ ls | into list -adfa
   ·                 ┬
   ·                 ╰── unknown flag
   ╰────
  help: Available flags: --help(-h). Use `--help` for more information.

In fact, I'd love to be able to optionally support every functionality that nushell supports with miette-style errors.

[amtoine]

completely support you here @fdncred 👍
i even opened an issue about that a while back 😉

• add more flexibility to custom errors in error make #8507

[KAAtheWiseGit]

@amtoine I checked it out and it turns out the help option was added to GenericError since then. I think this means we can kill two birds with one stone here.

[amtoine]

@KAAtheWiseGit
oh yeah, if we can kill these two birds at once, i'd be super happy to have a more powerful and easier to use error make 😇