How to best support inline definitions?

[Kheirlb]

Hi Langium folks,

Really cool tool. I really want to support "inline" definitions in my DSL, but that seems to break autocomplete. Any idea on how to debug or resolve? I see getCompletion being called, but not completionFor. I tried to create a simple example based off of hello world.

Langium

entry Model:
    (types+=AnimalType | animals+=Animal | greetings+=Greetings)*;

AnimalType:
    'animal' name=ID;

Animal:
    name=ID ':' type=[AnimalType];

Greetings:
  start=Greeting targets+=Target+;

Target:
    '-->' Greeting;

Greeting:
    GreetingRef | GreetingNew;

GreetingRef:
    ref=[Animal:ID];

GreetingNew:
    new=Animal;

The DSL file

animal Dog
animal Cat
dog1: Dog
dog2: Dog
cat1: Cat

dog1 --> dog2 --> cat1 --> cat2: Cat --> dog1

cat2 technically works once it is all typed out (I can rename symbol for example). It is just the suggestions do not appear like they do when defining top level. Thanks!

[msujew]

Hey @Kheirlb,

I've restructured your grammar a bit, so this use case is supported (at least within the same greeting chain). See this playground link. In here, cat2 shows up in the code completion.

To explain this a bit in detail: When defining an element inline (or rather, further down in the abstract syntax tree), it is only visible for its own sibling elements and its descendents. This is the default behavior, because it essentially implements lexical scoping from other programming languages and is useful for most languages. This behavior can be changed by adjusting the ScopeComputation, see also this guide which goes into that topic.

The fix in the ScopeComputation is to make the element visible on a different level - i.e. the root level or similar.

[Kheirlb]

Okay. I got the debugger working with the yeomin launch config. Thank you both! I added some uneducated thoughts to #1370 from what I could understand.

It's theoretically fixable in your specific language,

Are you saing I can implement a workaround for just my DSL?

[msujew]

You can try to force-update the chevrotain-allstar dependency in your project to 0.4.2 - that should probably fix the issue. Can you try that?

[Kheirlb]

0.4.2 works! (but sadly, not 0.4.3...)

Edit: You can see my testing on my project here Kheirlb/kassa#12 I tried to include some steps to reproduce. Maybe (likely) I just have some bad grammar design that can be cleaned up to work better on 0.4.3? Or maybe a 0.4.4 version could resolve the issue?

[msujew]

0.4.3 will work, but requires a new Langium release. I'll get out a patch release later today. 0.4.2 unfortunately broke some behavior, see #2146.

Edit: Langium 4.2.3 with that update has been released.

[Kheirlb]

It works! Thank you so much!

[Kheirlb]

(somewhat related, but would this have been an issue in Fastbelt? i don't actually need the performance gains for my little project, but I also wouldn't mind giving go/fastbelt a try if it might avoid bugs like this)

[msujew]

We will likely be able to avoid this in fastbelt, because we're writing our own parser engine. However, completion is a rather technically difficult topic and so it will likely still take a few weeks until we will get to it.