llmx/codex-rs/apply-patch/src/seek_sequence.rs

/// Attempt to find the sequence of `pattern` lines within `lines` beginning at or after `start`.
/// Returns the starting index of the match or `None` if not found. Matches are attempted with
/// decreasing strictness: exact match, then ignoring trailing whitespace, then ignoring leading
/// and trailing whitespace. When `eof` is true, we first try starting at the end-of-file (so that
/// patterns intended to match file endings are applied at the end), and fall back to searching
/// from `start` if needed.
///
/// Special cases handled defensively:
///  • Empty `pattern` → returns `Some(start)` (no-op match)
///  • `pattern.len() > lines.len()` → returns `None` (cannot match, avoids
///    out‑of‑bounds panic that occurred pre‑2025‑04‑12)
pub(crate) fn seek_sequence(
    lines: &[String],
    pattern: &[String],
    start: usize,
    eof: bool,
) -> Option<usize> {
    if pattern.is_empty() {
        return Some(start);
    }

    // When the pattern is longer than the available input there is no possible
    // match. Early‑return to avoid the out‑of‑bounds slice that would occur in
    // the search loops below (previously caused a panic when
    // `pattern.len() > lines.len()`).
    if pattern.len() > lines.len() {
        return None;
    }
    let search_start = if eof && lines.len() >= pattern.len() {
        lines.len() - pattern.len()
    } else {
        start
    };
    // Exact match first.
    for i in search_start..=lines.len().saturating_sub(pattern.len()) {
        if lines[i..i + pattern.len()] == *pattern {
            return Some(i);
        }
    }
    // Then rstrip match.
    for i in search_start..=lines.len().saturating_sub(pattern.len()) {
        let mut ok = true;
        for (p_idx, pat) in pattern.iter().enumerate() {
            if lines[i + p_idx].trim_end() != pat.trim_end() {
                ok = false;
                break;
            }
        }
        if ok {
            return Some(i);
        }
    }
    // Finally, trim both sides to allow more lenience.
    for i in search_start..=lines.len().saturating_sub(pattern.len()) {
        let mut ok = true;
        for (p_idx, pat) in pattern.iter().enumerate() {
            if lines[i + p_idx].trim() != pat.trim() {
                ok = false;
                break;
            }
        }
        if ok {
            return Some(i);
        }
    }
    None
}

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

    fn to_vec(strings: &[&str]) -> Vec<String> {
        strings.iter().map(|s| s.to_string()).collect()
    }

    #[test]
    fn test_exact_match_finds_sequence() {
        let lines = to_vec(&["foo", "bar", "baz"]);
        let pattern = to_vec(&["bar", "baz"]);
        assert_eq!(seek_sequence(&lines, &pattern, 0, false), Some(1));
    }

    #[test]
    fn test_rstrip_match_ignores_trailing_whitespace() {
        let lines = to_vec(&["foo   ", "bar\t\t"]);
        // Pattern omits trailing whitespace.
        let pattern = to_vec(&["foo", "bar"]);
        assert_eq!(seek_sequence(&lines, &pattern, 0, false), Some(0));
    }

    #[test]
    fn test_trim_match_ignores_leading_and_trailing_whitespace() {
        let lines = to_vec(&["    foo   ", "   bar\t"]);
        // Pattern omits any additional whitespace.
        let pattern = to_vec(&["foo", "bar"]);
        assert_eq!(seek_sequence(&lines, &pattern, 0, false), Some(0));
    }

    #[test]
    fn test_pattern_longer_than_input_returns_none() {
        let lines = to_vec(&["just one line"]);
        let pattern = to_vec(&["too", "many", "lines"]);
        // Should not panic – must return None when pattern cannot possibly fit.
        assert_eq!(seek_sequence(&lines, &pattern, 0, false), None);
    }
}