[antlr-interest] Tree parser tree building bug and workaround

[Monty Zukowski]

Oh, actually my rule did call subrules instead of just terminals.
Here's a simple example, just for looking at the generated code.
functionBad generates code which overwrites the built AST.
functionGood generates code which builds and preserves the AST
properly.

class Test extends TreeParser;
options {
	buildAST=true;
}

functionBad
    :
    #(f:FUNCTION
	      (functionBad)*
	      {##=#(#[FUNCTION],##);}
	     )
    ;

functionGood
    :
    #(f:FUNCTION
	      (functionGood)*
	     )
	      {##=#(#[FUNCTION],##);}
    ;
On 11/29/06, Ric Klaren <ric.klaren at gmail.com> wrote:
> Hi,
>
> On 11/29/06, Monty Zukowski <monty at codetransform.com> wrote:
> > On 11/29/06, Micheal J <open.zone at virgin.net> wrote:
> > > Hi Monty,
> > >
> > > > I just found a bug in 2.7.7 (and 2.7.4).  I have a tree
> > > > parser rule that builds a tree (just adding a new parent
> > > > node), like this:
> > > >
> > > > rule1:
> > > > #( T1 T2 T3
> > > >   { ##=#(#[NEWROOT],##); }
> > > >   )
> > > >   ;
> > >
> > > Shouldn't that be:
> > >
> > > Rule1
> > >   :  #( T1 T2 T3
> > >      )
> > >      { ##=#(#[NEWROOT],##); }
> > >   ;
> > >
> > > With the action block following the tree pattern matching specification.
> > >
> > > > >From inside the action, I see that the tree is built properly.  But
> > > > for some reason, upon exit of the rule the AST for rule1 is
> > > > replaced by the original.  (You can see it in the generated code).
> > >
> > > This resonates with my preposition that action block placement might be the
> > > issue here.
> > >
> >
> > I suppose that is it, but I don't understand why.  What does it
> > matter?  I would expect the root to be built after T1 has been
> > matched.  Why can't I manipulate it from inside the #() ?
>
> This is probably an artifact of how the code gets generated for the #(
> .. ). After the closing ')' of the #() some code is probably emitted
> that borks the ## pointer/reference or something similar. Hmm those
> T1..3 are those terminals or subrules in your case? Or I'm missing
> something or I made my example .g file to simple.....
>
> Cheers,
>
> Ric
>