No way to propagate error from callback

[stepancheg]

Consider this example:

fn parse_int(lex: &Lexer<Token>) -> ??? {
  lex.slice().parse::<i32>()
}

enum Token {
  #[error]
  Error,

  #[regex("[0-9]+"), parse_int]
  Int(i32),

  #[regex(...), parse_string_literal]
  StringLiteral,
}

Parse errors are converted to Token::Error which contains no information. There's no way (to my knowledge) to propagate parse_int or parse_string_literal error to the caller.

[daprahamian]

Wanted to second this. I am trying to propagate an error out from one of my token parsers, but it appears there is no way to map the Error token to something else?

[andrewhickman]

As a workaround, you can store extra error information inside the extras field of the lexer

fn parse_int(lex: &mut Lexer<Token>) -> Result<i32, ()> {
  match lex.slice().parse::<i32>() {
    Ok(value) => Ok(value),
    Err(err) => {
      lex.extras.errors.push(err.into());
      Err(())
    }
}

#[derive(Default)]
struct TokenExtras {
    errors: Vec<MyErrorType>,
}

#[derive(Logos)]
#[logos(extras = TokenExtras)]
enum Token {
  #[error]
  Error,
  #[regex("[0-9]+"), parse_int]
  Int(i32),
}