jsslint-core 1.0.0

Core rule engine for the JSS style checker (spec 018 Rust port).
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//! `pos_to_lineno_colno` port — mirrors `pylatexenc.latexwalker`'s
//! method of the same name (empirically verified: 1-based line, 0-based
//! column, both counted in codepoints, splitting on `\n`).
//!
//! `_helpers.py::_lineno_col` then adds 1 to the column to get the
//! 1-based column `Violation` actually carries — that final `+1` step
//! belongs to the rule layer (Phase 3), not here; this module only
//! reproduces the walker-level primitive.

/// Precomputed newline codepoint-offsets for O(log n) line lookup —
/// same idea as `pylatexenc`'s internal line-boundary cache.
pub struct LineIndex {
    /// Offset of each `\n` character in the source.
    newline_positions: Vec<usize>,
}

impl LineIndex {
    pub fn new(chars: &[char]) -> Self {
        let newline_positions = chars
            .iter()
            .enumerate()
            .filter(|(_, &c)| c == '\n')
            .map(|(i, _)| i)
            .collect();
        Self { newline_positions }
    }

    /// Returns `(1-based line, 0-based column)`, both in codepoints.
    pub fn lineno_colno(&self, pos: usize) -> (u32, u32) {
        // Number of newlines strictly before `pos` = 0-based line index.
        let line_idx = self.newline_positions.partition_point(|&nl| nl < pos);
        let line = (line_idx + 1) as u32;
        let line_start = if line_idx == 0 {
            0
        } else {
            self.newline_positions[line_idx - 1] + 1
        };
        let col = (pos - line_start) as u32;
        (line, col)
    }
}