Scoping in Xtext

Question

I have troubles with understanding how i can influence the scoping. assume i have simple grammar:

Model:
    def = DefVarList
    (use = UseList)?
;

DefVarList:
    name = 'def' '{' (list += DefVar)* '}'
;

DefVar:
    name = ID ';'
;

UseList:
    name = 'use' '{'
        (list += UseVar)* 
    '}'
;

UseVar:
    name = [DefVar] ';'
;

of course, writing something like

def {   qwerty;  }
use {   qwerty;  }

results error, because one couldn't resolve a reference. So i went to ScopeProvider class and rewrite it:

public class TestgrammarScopeProvider extends AbstractTestgrammarScopeProvider{
    public IScope scope_UseVar_name(UseVar v, EReference ref) {
        Model m = (Model)v.eContainer().eContainer();
        return Scopes.scopeFor(m.getDef().getList());
    }
}

This doesn't working. It doesn't even call this function. What am i doing wrong?

P.S. i know about inserting fragment line in my mwe2 file, but i wonder why this program doesnt call this function.

The scope_ methods work only if your scopeprovider inherits from abstractdeclarativescopeprovider - this is no longer the case in xtext 2.9+ — Christian Dietrich

systemcpro systemcpro · Accepted Answer · 2016-05-20T16:03:54

You are using a cross reference as an identifier in UseVar. I changed that to

UseVar: ref=[DefVar] ';'

Then this xtend snippets works for your DSL.

override IScope getScope(EObject context, EReference ref){
    if(context instanceof UseVar && ref == USE_VAR__REF){
        val model = context.getContainerOfType(Model)

        val defVarList = model.def.list         
        return Scopes::scopeFor(defVarList)
    }
    return IScope::NULLSCOPE
}

Am also assuming this is just a starting demo to get your project going but you might consider removing some of the syntactic noise such using this for a list instead

 List items+=rule (',' items+=rule)*;

or perhaps removing the curly braces too (but you may want nested blocks later in which case you may need them). Only you can tell but its worth considering.

Scoping in Xtext

1 Answers