Creating your own errors

Using the metadata information, you can create your own custom error messages. Error messages are built of multiple parts:

  • The title of the error
  • The label of error message, which includes both the text of the label and the span to underline

You can use the error make command to create your own error messages. For example, let’s say you had your own command called my-command and you wanted to give an error back to the caller about something wrong with a parameter that was passed in.

First, you can take the span of where the argument is coming from:

  1. let span = (metadata $x).span;

Next, you can create an error using the error make command. This command takes in a record that describes the error to create:

  1. error make {msg: "this is fishy", label: {text: "fish right here", start: $span.start, end: $span.end } }

Together with your custom command, it might look like this:

  1. def my-command [x] {
  2.     let span = (metadata $x).span;
  3.     error make {
  4.         msg: "this is fishy",
  5.         label: {
  6.             text: "fish right here",
  7.             start: $span.start,
  8.             end: $span.end
  9.         }
  10.     }
  11. }

When called with a value, we’ll now see an error message returned:

  1. > my-command 100
  3. Error:
  4.   × this is fishy
  5.    ╭─[entry #5:1:1]
  6.  1 │ my-command 100
  7.    ·            ─┬─
  8.    ·             ╰── fish right here
  9.    ╰────