Parser: array subscript reader stops at first ] ignoring nested ${...}

[chaliy]

Bug

The parser's array subscript reader in parser/mod.rs stops at the first ] character without tracking nesting. For expressions like:

${names[$RANDOM % ${#names[@]}]}

the subscript is read as $RANDOM % ${#names[ — stopping at the ] inside ${#names[@]} — instead of the full $RANDOM % ${#names[@]}.

Root cause

Around line 2390 in parse_word(), the subscript reader is:

while let Some(&c) = chars.peek() {
    if c == ']' {
        chars.next();
        break;
    }
    index.push(chars.next().unwrap());
}

No bracket or brace depth tracking.

Fix

Track [] bracket depth and ${} brace depth when reading subscript content, so nested expressions don't prematurely end the subscript.