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

[Monty Zukowski]

Hi all,

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],##); }
  )
  ;

>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).

I didn't track down the problem in ANTLR itself.  However, I found a workaround:

rule1:
  subruleT1 { ##=#(#[NEWROOT],##); }
  ;

subruleT1
  : #( T1 T2 T3 )
  ;

Monty