Function find_enclosing_open_paren

src/completion/named_args.rs:162–196

Walk backward from `start` (exclusive) to find the unmatched `(` that encloses the cursor. Skips balanced `(…)` pairs and string literals. Returns `None` if no enclosing `(` is found (cursor is not inside call parens).

(chars: &[char], start: usize)

/// Skips balanced `(…)` pairs and string literals.  Returns `None` if no
/// enclosing `(` is found (cursor is not inside call parens).
pub fn find_enclosing_open_paren(chars: &[char], start: usize) -> Option<usize> {
    let mut i = start;
    let mut depth: i32 = 0;

    while i > 0 {
        i -= 1;
        match chars[i] {
            ')' => depth += 1,
            '(' => {
                if depth > 0 {
                    depth -= 1;
                } else {
                    // Found unmatched `(` — this is the call's open paren.
                    return Some(i);
                }
            }
            // Skip single-quoted strings backwards
            '\'' => {
                i = skip_string_backward(chars, i, '\'');
            }
            // Skip double-quoted strings backwards
            '"' => {
                i = skip_string_backward(chars, i, '"');
            }
            // If we hit `{` or `[` without a matching `}` or `]`, we've
            // left the expression context — stop searching.
            '{' | '[' => return None,
            // If we hit `;` we've gone past a statement boundary.
            ';' => return None,
            _ => {}
        }
    }

    None
}

/// Skip backward past a string literal ending at position `end` (which
/// points to the closing quote character `q`).