Function line_starts

pub fn line_starts<'source>(
    source: &'source str,
) -> impl 'source + Iterator<Item = usize>

Return the starting byte index of each line in the source string.

This can make it easier to implement Files::line_index by allowing implementors of Files to pre-compute the line starts, then search for the corresponding line range, as shown in the example below.

Example

use codespan_reporting::files;

let source = "foo\nbar\r\n\nbaz";
let line_starts: Vec<_> = files::line_starts(source).collect();

assert_eq!(
    line_starts,
    [
        0,  // "foo\n"
        4,  // "bar\r\n"
        9,  // ""
        10, // "baz"
    ],
);

fn line_index(line_starts: &[usize], byte_index: usize) -> Option<usize> {
    match line_starts.binary_search(&byte_index) {
        Ok(line) => Some(line),
        Err(next_line) => Some(next_line - 1),
    }
}

assert_eq!(line_index(&line_starts, 5), Some(1));