[antlr-interest] Re: Backtrack option breaks AST rewrite

[Thomas Brandon]

I found another issue with backtracking. With backtrack and memoize on
the use of labels can result in invalid code. For example the
following grammar:
grammar BTErr2;
options {
 backtrack=true;
 memoize=true;
 k=2;
 output=AST;
}
a: 'c' dl=d
 | 'c' d
 ;
d: 'd' ;

gives java error "dl cannot be resolved" in BTErr2.java. The
combination of backtracking and memoization results in ANTLR
generating a syntactic predicate "( 'c' dl= d )=>", which is
implemented in a synpred1_fragment method, with the label assignment
resulting in "dl=d();" but dl is not defined in the synpred method.

Tom.