incorrect optional arguments signature validation

[mikhail-barg]

I have been updating my C# jsonata port to pass latest signature tests when I stumbled upon something that looks like an unexpwected behaviour to me:

jsonata/src/signature.js

Lines 230 to 254 in 597e5ee

	params.forEach(function (param, index) {
	var arg = args[argIndex];
	var match = isValid[index + 1];
	if (match === '') {
	if (param.context && param.contextRegex) {
	// substitute context value for missing arg
	// first check that the context value is the right type
	var contextType = getSymbol(context);
	// test contextType against the regex for this arg (without the trailing ?)
	if (param.contextRegex.test(contextType)) {
	validatedArgs.push(context);
	} else {
	// context value not compatible with this argument
	throw {
	code: "T0411",
	stack: (new Error()).stack,
	value: context,
	index: argIndex + 1
	};
	}
	} else {
	validatedArgs.push(arg);
	argIndex++;
	}
	} else {

specifically, if there's an empty match for a param and param is not a context/contextRegex then the function would just silently validate current arg for the param.

This seem to be plainly wrong, and it would cause stuff like this:

λ($arg1, $arg2)<s?n?:o>{{"$arg1": $arg1, "$arg2": $arg2}}(2)

produces

{
  "$arg1": 2
}

instead of

{
  "$arg2": 2
}

https://try.jsonata.org/KS7syiOV_

And

λ($arg1, $arg2)<s?n?:o>{{"$arg1": $arg1, "$arg2": $arg2}}(1,2)

produces error (expected) with unexpected message: Argument 2 of function undefined does not match function signature — one would expect that it is argument 1 that does not match the signature.