[antlr-interest] A lost label?

[Markus Stoeger]

I ran into a nasty "ArgumentNullException" problem with the following 
rule today:

label returns [string name]
    : x=unsignedInt {$name = $x.text;}
    | x=identifier {$name = $x.text;}
    ;

The generated code (CSharp2) for this rule is below. For some reason 
ANTLR doesn't assign the label x in the first alternative which results 
in "name" being null all the time:

case 1 : {
        unsignedInt(); // missing assignment to label x!
        name =  ((x != null) ? 
input.ToString((IToken)(x.Start),(IToken)(x.Stop)) : null);
        break;
    }
case 2 : {
        x = identifier();
        name =  ((x != null) ? 
input.ToString((IToken)(x.Start),(IToken)(x.Stop)) : null);
        break;
    }

If I call one label x and the other one y it works fine (both get assigned).

Shouldn't it be possible to use the x label for both assignments, since 
they are assigned in two different alternatives? The book (page 124) 
says "variables are visible to the immediately surrounding alternative, 
but not other alternatives". If I understand this right, each 
alternative has its own scope so reusing the variable name in another 
scope should be possible? Or maybe ANTLR could display an error while 
generating the parser in such a case? That would be better than silently 
discarding the assignment... :-)

Max