How can I prevent whitespaces in one parser rule when I already have hidden terminal WS?

[jindong-zhannng]

Hi team, I'd like to define a rule Annotation to express a java-like annotation syntax. Now it's like:

Annotation:
  '@' name=ID ('(' args+=DeclaredParameter (',' args+=DeclaredParameter)* ')')?;

Now since I have hidden terminal hidden terminal WS: /\s+/;, whitespaces between '@' and annotation name are allowed.

My expectation is the annotation body must be followed '@' without whitespaces, and semantic model should only contains annotation body without '@' sign.

How could I achieve it?

[msujew]

Hey @jindong-zhannng, basically you have two options:

1. Keep it as it is now and add a validation that shows an error in case there is space between the @ keyword and the name property.
2. Define a new terminal like this terminal AnnotationName: '@' ID; and use it as the name property. Make sure to override the DefaultValueConverter to remove the @ character from the parsed value.

Note that I would recommend the first approach, as it makes parsing more error tolerant, and custom validations usually lead to better error messages for end users.