Why Would This Resolve as a BinaryExpression in Validation?

[ballcoach12]

Given the grammar and example shown here, the variable declaration (var x:string[] = ["a", 1];) is presented as a BinaryExpression to my validation routines, and subsequently as a VariableDeclaration to my validation routines. But in the AST it is a VariableDeclaration, which is correct.

I can maybe see why it might look like a BinaryExpression given the array initializer, but I cannot figure out why it would appear as both to validation. I've checked my dependency injection code to make sure that I'm mapping the correct AstNode to the correct validation routine, and Chevrotain is not complaining about ambiguous rules or paths.

I'm not sure what is going on here.

[msujew]

Chevrotain is not complaining about ambiguous rules or paths

Actually chevrotain is complaining about your rule. See playground console log:

Ambiguous Alternatives Detected: <0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 1> in <OR1> inside <VariableDeclaration​> Rule,
<string, [, ], =, [> may appears as a prefix path in all these alternatives.
See: https://chevrotain.io/docs/guide/resolving_grammar_errors.html#AMBIGUOUS_ALTERNATIVES
For Further details.

In particular the type=(TypeReference | UnionType))? alternative is ambiguous. See here on how to write a union type rule using actions in a non-ambiguous way.

I've just tried reproducing the issue on the latest version of Langium (2.1.0), but on my end the validation for a BinaryExpression is never triggered.

[ballcoach12]

Thanks so much, Mark! I totally missed the Chevrotain error in the playground. The union types are a new feature in my language and I haven't been too happy so far with how my implementation works. I'll definitely look at the link!

[ballcoach12]

I've just tried reproducing the issue on the latest version of Langium (2.1.0), but on my end the validation for a BinaryExpression is never triggered.

I see this behavior as well. I have two unit tests that validate the exact same concrete syntax. In one case it shows up as a BinaryExpression and also a VariableDeclaration; in the other, it only shows up as a VariableDeclaration.

[spoenemann]

We should fix this to improve Playground usability: eclipse-langium/langium-website#130