[antlr-interest] Null variable value for tree grammar rule variables

[Gavin Lambert]

At 13:09 28/02/2008, Matthieu Riou wrote:
>assign  :       ^(ASSIGN lv=(path_expr) rv=(rvalue)) { 
>builder.build(OAssign.class, $BPELScope::oscope, 
>$Parent::activity, $lv, $rv); };
>
>In the above method call both $lv and $rv are null. When I check 
>the generated class the two local variables lv and rv are 
>properly defined but never assigned to. Note that I've only 
>observed this behavior when the variables are set as being the 
>tree resulting from a subrule, not for a plain token.

This rings a bell.  I think if you remove the parentheses, the 
problem should go away.  ie. change the rule to this:

assign : ^(ASSIGN lv=path_expr rv=rvalue) { 
builder.build(OAssign.class, $BPELScope::oscope, 
$Parent::activity, $lv, $rv); };

The problem is that anything in parentheses is a block, and you 
can't assign a name to a block, only to a single rule/token.