typechecking

With Closure Compiler v20210106 and the following flags:

--language_in=ECMASCRIPT_NEXT
--compilation_level ADVANCED
--js tmp/wrap.js 

This works fine:

/**
 * @param {string} str
 * @param {string} [prefix=aa]
 * @param {string} [suffix=bb]
 */
function wrap1(str, prefix="aa", suffix="bb") {
  return prefix + str + suffix;
}

window.wrap1 = wrap

fn __invoke() {
	xs := array{1; 2; 3;};
	i := 1;
	return xs[i];
};

Makes the program crash in Value::get_integer. I used a hack to make asan give me a stack trace:

    #0 0x55be6f608903 in Interpreter::Value::get_integer() src/interpreter/value.hpp:80
    #1 0x55be6f604cec in Interpreter::eval(AST::IndexExpression*, Interpreter::Interpreter&) src/interpreter/eval.cpp:18