How to disambiguate invalid parens, f.e. ();, from valid arrow function, f.e. () => {}

[trusktr]

We have the following expression to detect "invalid" empty parens by having the validator mark the valid syntax as invalid:

https://github.com/bytescript/bytescript/blob/bddbe1b452cbcba256d761a3f391f9ea63c8ebb9/src/language-server/bytescript.langium#L92-L93

InvalidParenthesis:
	empty?="(" ")";

I'm also trying to add arrow function syntax into the grammar,

https://github.com/bytescript/bytescript/blob/bddbe1b452cbcba256d761a3f391f9ea63c8ebb9/src/language-server/bytescript.langium#L119

ArrowFunctionExpression:
	Parameters (":" ReturnType)? "=>" body=(ArrowReturnExpression | Block);

where Parameters is a fragment with "(" ... ")", however it conflicts with the InvalidParenthesis rule, so when I try to write an arrow function in my sample code, I get an error regarding the invalid parens instead.

For example, this is invalid code that the validator should flag,

();

while this is valid code:

const f = () => {}

How can we achieve having both of those things in the language?

[msujew]

It seems like ArrowFunctionExpression is currently unused, right? I've tried your current main with a minor change:

FunctionDeclaration:
-	OriginalFunctionDeclaration | GeneratorFunctionDeclaration;
+	OriginalFunctionDeclaration | GeneratorFunctionDeclaration | ArrowFunctionExpression;

That seems to work as expected:

[trusktr]

Ah, ok! Simple things make a difference. Thanks!