helix-plus/helix-core/src/match_brackets.rs

use tree_sitter::Node;

use crate::{Rope, Syntax};

const MAX_PLAINTEXT_SCAN: usize = 10000;

// Limit matching pairs to only ( ) { } [ ] < > ' ' " "
const PAIRS: &[(char, char)] = &[
    ('(', ')'),
    ('{', '}'),
    ('[', ']'),
    ('<', '>'),
    ('\'', '\''),
    ('\"', '\"'),
];

/// Returns the position of the matching bracket under cursor.
///
/// If the cursor is on the opening bracket, the position of
/// the closing bracket is returned. If the cursor on the closing
/// bracket, the position of the opening bracket is returned.
///
/// If the cursor is not on a bracket, `None` is returned.
///
/// If no matching bracket is found, `None` is returned.
#[must_use]
pub fn find_matching_bracket(syntax: &Syntax, doc: &Rope, pos: usize) -> Option<usize> {
    if pos >= doc.len_chars() || !is_valid_bracket(doc.char(pos)) {
        return None;
    }
    find_pair(syntax, doc, pos, false)
}

// Returns the position of the bracket that is closing the current scope.
//
// If the cursor is on an opening or closing bracket, the function
// behaves equivalent to [`find_matching_bracket`].
//
// If the cursor position is within a scope, the function searches
// for the surrounding scope that is surrounded by brackets and
// returns the position of the closing bracket for that scope.
//
// If no surrounding scope is found, the function returns `None`.
#[must_use]
pub fn find_matching_bracket_fuzzy(syntax: &Syntax, doc: &Rope, pos: usize) -> Option<usize> {
    find_pair(syntax, doc, pos, true)
}

fn find_pair(syntax: &Syntax, doc: &Rope, pos: usize, traverse_parents: bool) -> Option<usize> {
    let tree = syntax.tree();
    let pos = doc.char_to_byte(pos);

    let mut node = tree.root_node().named_descendant_for_byte_range(pos, pos)?;

    loop {
        let (start_byte, end_byte) = surrounding_bytes(doc, &node)?;
        let (start_char, end_char) = (doc.byte_to_char(start_byte), doc.byte_to_char(end_byte));

        if is_valid_pair(doc, start_char, end_char) {
            if end_byte == pos {
                return Some(start_char);
            }
            // We return the end char if the cursor is either on the start char
            // or at some arbitrary position between start and end char.
            return Some(end_char);
        }

        if traverse_parents {
            node = node.parent()?;
        } else {
            return None;
        }
    }
}

/// Returns the position of the matching bracket under cursor.
/// This function works on plain text and ignores tree-sitter grammar.
/// The search is limited to `MAX_PLAINTEXT_SCAN` characters
///
/// If the cursor is on the opening bracket, the position of
/// the closing bracket is returned. If the cursor on the closing
/// bracket, the position of the opening bracket is returned.
///
/// If the cursor is not on a bracket, `None` is returned.
///
/// If no matching bracket is found, `None` is returned.
#[must_use]
pub fn find_matching_bracket_current_line_plaintext(
    doc: &Rope,
    cursor_pos: usize,
) -> Option<usize> {
    // Don't do anything when the cursor is not on top of a bracket.
    let bracket = doc.char(cursor_pos);
    if !is_valid_bracket(bracket) {
        return None;
    }

    // Determine the direction of the matching.
    let is_fwd = is_forward_bracket(bracket);
    let chars_iter = if is_fwd {
        doc.chars_at(cursor_pos + 1)
    } else {
        doc.chars_at(cursor_pos).reversed()
    };

    let mut open_cnt = 1;

    for (i, candidate) in chars_iter.take(MAX_PLAINTEXT_SCAN).enumerate() {
        if candidate == bracket {
            open_cnt += 1;
        } else if is_valid_pair(
            doc,
            if is_fwd {
                cursor_pos
            } else {
                cursor_pos - i - 1
            },
            if is_fwd {
                cursor_pos + i + 1
            } else {
                cursor_pos
            },
        ) {
            // Return when all pending brackets have been closed.
            if open_cnt == 1 {
                return Some(if is_fwd {
                    cursor_pos + i + 1
                } else {
                    cursor_pos - i - 1
                });
            }
            open_cnt -= 1;
        }
    }

    None
}

fn is_valid_bracket(c: char) -> bool {
    PAIRS.iter().any(|(l, r)| *l == c || *r == c)
}

fn is_forward_bracket(c: char) -> bool {
    PAIRS.iter().any(|(l, _)| *l == c)
}

fn is_valid_pair(doc: &Rope, start_char: usize, end_char: usize) -> bool {
    PAIRS.contains(&(doc.char(start_char), doc.char(end_char)))
}

fn surrounding_bytes(doc: &Rope, node: &Node) -> Option<(usize, usize)> {
    let len = doc.len_bytes();

    let start_byte = node.start_byte();
    let end_byte = node.end_byte().saturating_sub(1);

    if start_byte >= len || end_byte >= len {
        return None;
    }

    Some((start_byte, end_byte))
}

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

    #[test]
    fn test_find_matching_bracket_current_line_plaintext() {
        let assert = |input: &str, pos, expected| {
            let input = &Rope::from(input);
            let actual = find_matching_bracket_current_line_plaintext(input, pos);
            assert_eq!(expected, actual.unwrap());

            let actual = find_matching_bracket_current_line_plaintext(input, expected);
            assert_eq!(pos, actual.unwrap(), "expected symmetrical behaviour");
        };

        assert("(hello)", 0, 6);
        assert("((hello))", 0, 8);
        assert("((hello))", 1, 7);
        assert("(((hello)))", 2, 8);

        assert("key: ${value}", 6, 12);
        assert("key: ${value} # (some comment)", 16, 29);

        assert("(paren (paren {bracket}))", 0, 24);
        assert("(paren (paren {bracket}))", 7, 23);
        assert("(paren (paren {bracket}))", 14, 22);

        assert("(prev line\n ) (middle) ( \n next line)", 0, 12);
        assert("(prev line\n ) (middle) ( \n next line)", 14, 21);
        assert("(prev line\n ) (middle) ( \n next line)", 23, 36);
    }
}