False negatives while writing a new typed declaration

[lou1306]

Thank you for Typir, it's an excellent framework to work with!

We have a DSL with builtin types such as int and bool, pretty standard (typed) variable declarations such as x: bool; the user may also define custom enumerations like enum myEnum {foo, bar, baz}.

Typir works perfectly most of the time, it is also pretty reactive to report or clear type errors when making changes in expressions, etc. However, if one tries to declare a new variable, say y: bool, and starts typing down the letters 'b', 'o', 'o', 'l', the following error messages appear:

Could not resolve reference to Enum named 'b'.
Could not resolve reference to Enum named 'bo'.
Could not resolve reference to Enum named 'boo'.

It seems that Typir is eagerly looking to type-check the file and fails to find a primitive type b not a b enumeration, triggering the error. Indeed, if I copy-paste the entire y: bool declaration, no error is triggered. Furthermore, the errors do not disappear even after the type is spelt out in full.

Is there something we are missing in Typir's execution "lifecycle"?

[JohannesMeierSE]

Hello @lou1306,

thanks for the feedback!

The Typir types are created after indexing and before linking. Since required references are resolved by Langium on request even before the "official linking phase", there should be no problem in general.

Errors like Could not resolve reference to Enum named 'b'. are created by Langium, not by Typir. But Typir might triggered Langium to resolve this reference: Do you have a reproducible example and a stack trace? That would be nice for further investigations.

Inside your inference rules, you need to take care about non-resolved cross-references yourself, e.g.

typir.Inference.addInferenceRulesForAstNodes({
    EnumLiteralUse: (languageNode) => {
        const ref = languageNode.literal.ref;
        if (isEnumLiteral(ref)) {
            return ref;
        } else if (ref === undefined) {
            return InferenceRuleNotApplicable; // found non-resolved cross-reference
        } else {
            ...
        }
    },
});

Maybe this check is missing?

[lou1306]

Thank you for your reply! It steered us in the right direction.

Somehow, when ref is undefined something goes awry with Langium, even with the suggested checks, and those error messages I mentioned are not cleared up. At the moment we worked around this issue by using $refText and directly looking up the corresponding type (if one exists) with typir.factory.Primitives.get. I suspect this might have something to do with some not-great choice we made in the grammar.

I should also add (and apologies for not mentioning it earlier) that we are working on Langium 3.5.0/Typir 0.2.2. Maybe a more recent version would solve this for us, but we haven't looked into updating yet.