Support for converting line-column pair into byte offset

[segeljakt]

It is currently possible to convert a byte offset into a line-column pair using Source::get_byte_line, but don't see a way to do the inverse operation. It would be a very useful feature when interoperating with LSP, which uses line-column pairs. Is it possible to add? I think it might be enough to make the method Line::byte_span public.

[adclz]

For those of you who are struggling to convert LSP diagnostic position encodings, here's one way to do it:

let range = diagnostic.range; // Diagnostic from lsp_types
let start_line = source.line(range.start.line as usize).unwrap().offset();
let end_line = source.line(range.end.line as usize).unwrap().offset();
let start = start_line + range.start.character as usize;
let end = end_line + range.end.character as usize;

let label = Label::new(start..end).with_message(format!("{}", diagnostic.message.clone()));