ktrs-lint 0.5.1

Port of the ktlint 2.0 rule engine and standard rules over the ktrs mutable AST
Documentation 
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//! Port of ktlint-rule-engine `PositionInTextLocator.kt`. Offsets are UTF-16 units, as on the JVM.

/// `buildPositionInTextLocator(text)`: segment `i` spans `[starts[i], starts[i + 1] - 1]`.
pub struct PositionInTextLocator {
    starts: Vec<usize>,
}

impl PositionInTextLocator {
    pub fn new(text: &str) -> PositionInTextLocator {
        let mut starts = vec![0];
        let mut units = 0;
        for c in text.chars() {
            units += c.len_utf16();
            if c == '\n' {
                starts.push(units);
            }
        }
        let text_length = units;
        let last = *starts.last().unwrap();
        starts.push(text_length + usize::from(last == text_length));
        PositionInTextLocator { starts }
    }

    /// `(line, col)`, both 1-based; `(1, 1)` for an offset past the last segment (`SegmentTree.indexOf == -1`).
    pub fn locate(&self, offset: usize) -> (usize, usize) {
        let segments = &self.starts[..self.starts.len() - 1];
        if offset >= *self.starts.last().unwrap() {
            return (1, 1);
        }
        let line = segments.partition_point(|&start| start <= offset) - 1;
        (line + 1, offset - segments[line] + 1)
    }
}

#[cfg(test)]
mod tests {
    use super::PositionInTextLocator;

    #[test]
    fn segments_like_the_segment_tree() {
        let l = PositionInTextLocator::new("ab\ncd");
        assert_eq!([l.locate(0), l.locate(2), l.locate(3), l.locate(4)], [(1, 1), (1, 3), (2, 1), (2, 2)]);
        assert_eq!(l.locate(5), (1, 1), "end of text without a trailing newline is outside every segment");
        let l = PositionInTextLocator::new("ab\n");
        assert_eq!(l.locate(3), (2, 1));
        let l = PositionInTextLocator::new("é\nx");
        assert_eq!(l.locate(2), (2, 1), "UTF-16 units");
    }
}