[antlr-interest] Bug in ANTLR-3.1.2 with tree grammar wildcard list label x+= ?

[Laurent Caillette]

Hi all,

I attempted to switch to ANTLR-3.1.2, and the Java code generated from
my grammar doesn't compile anymore.

I've something like this:

part
  : ( mediumbreak | largebreak )?

    (   p += levelIntroducer
      | p += paragraph
      | p += blockQuote
      | p += literal
      | p += bigDashedListItem
      | p += cellRowSequence
    )
    ( largebreak (
        p += levelIntroducer
      | p += paragraph
      | p += blockQuote
      | p += literal
      | p += bigDashedListItem
      | p += cellRowSequence
    ) )*
    ( mediumbreak | largebreak )?
    EOF
    -> ^( PART $p+ )
  ;

Here is a piece of generated code:

            switch (alt2) {
                case 1 :
                    //
/Users/Shared/Novelang/src/antlr/Novelang.g:120:9: p+= levelIntroducer
                    {
                    pushFollow(FOLLOW_levelIntroducer_in_part485);
                    p=levelIntroducer();

And the compiler doesn't like generated code, it spits errors like this:

/Users/Shared/Scratch/Novelang/antlrworks/java/NovelangParser.java:754:
incompatible types
found   : NovelangParser.levelIntroducer_return
required: NovelangParser.cellRowSequence_return
                     p=levelIntroducer();
                                   ^

It seems that p has taken the type of the first rule
(levelIntroducer). Then attempting to set the result of
cellRowSequence doesn't work.

This happens consistently using ANTLRWorks-1.2.3 or antlr-3.1.2.jar directly.

In ANTLR-3.1.2 release notes there is something about the += operator:
<< Bug in code gen for tree grammar wildcard list label x+=. >>

Could my problem be related to this, or should I investigate some more?

Regards,

c.

P.S. The whole grammar can be found at :
http://github.com/caillette/novelang/raw/ef85822091680f3bca06ddc511386ec39fdb8b75/src/antlr/Novelang.g