Syntax error position for terminating ';' points to next statement

[ksjdragon]

For an example script like this:

use rhai::Engine;

fn main() {
    let engine = Engine::new();

    let main_script = r#"
let x = 1+2

let y = x;
y
"#
    .trim();

    let err = engine.eval::<i32>(main_script);
    println!("{err:?}");
}

The resulting error will be
Err(ErrorParsing(MissingToken(";", "to terminate this statement"), 3:1))
where 3:1 becomes "let y = x", that is, the statement after the missing statement.

I would assume this occurs because the parser will ignore whitespace until it scans a terminator, but
I think this makes the error message unclear, since it makes it look like the next statement is the one
that is missing the terminator.

If the parser doesn't keep track of spans, perhaps at least changing the message to be "expected terminator ; before this statement" or something of that nature.

[schungx]

That's correct. Rhai does not keep a span, so the last non-whitespace position is lost. We can probably keep this extra bit of info, or do as you say: change the error message.

However that would be a breaking change... So I suggest that you simply override Rhai's builtin error message text.

[ksjdragon]

How would you go about overriding it? Do you mean you simply replace the string after the error has been returned?

Why would changing the error message be a breaking change? Or do you mean that keeping the info would be a breaking change?

[schungx]

It would be a breaking change because some users may simply search for certain keywords in the error message as a quick 'n dirty way of error handling. Rhai's own test suite sometimes does this also... And others may depend on that position starting at the beginning of the next statement.

How would you go about overriding it?

You can have your own error_display, for example, that prints out tailored error messages different from Rhai's default. That's the way people provide translated error messages.