fn populate_used_symbols()

in cli/src/generate/build_tables/mod.rs [153:199]

• 41 lines of code
• 11 McCabe index (conditional complexity)

fn populate_used_symbols(
    parse_table: &mut ParseTable,
    syntax_grammar: &SyntaxGrammar,
    lexical_grammar: &LexicalGrammar,
) {
    let mut terminal_usages = vec![false; lexical_grammar.variables.len()];
    let mut non_terminal_usages = vec![false; syntax_grammar.variables.len()];
    let mut external_usages = vec![false; syntax_grammar.external_tokens.len()];
    for state in &parse_table.states {
        for symbol in state.terminal_entries.keys() {
            match symbol.kind {
                SymbolType::Terminal => terminal_usages[symbol.index] = true,
                SymbolType::External => external_usages[symbol.index] = true,
                _ => {}
            }
        }
        for symbol in state.nonterminal_entries.keys() {
            non_terminal_usages[symbol.index] = true;
        }
    }
    parse_table.symbols.push(Symbol::end());
    for (i, value) in terminal_usages.into_iter().enumerate() {
        if value {
            // Assign the grammar's word token a low numerical index. This ensures that
            // it can be stored in a subtree with no heap allocations, even for grammars with
            // very large numbers of tokens. This is an optimization, but it's also important to
            // ensure that a subtree's symbol can be successfully reassigned to the word token
            // without having to move the subtree to the heap.
            // See https://github.com/tree-sitter/tree-sitter/issues/258
            if syntax_grammar.word_token.map_or(false, |t| t.index == i) {
                parse_table.symbols.insert(1, Symbol::terminal(i));
            } else {
                parse_table.symbols.push(Symbol::terminal(i));
            }
        }
    }
    for (i, value) in external_usages.into_iter().enumerate() {
        if value {
            parse_table.symbols.push(Symbol::external(i));
        }
    }
    for (i, value) in non_terminal_usages.into_iter().enumerate() {
        if value {
            parse_table.symbols.push(Symbol::non_terminal(i));
        }
    }
}