[antlr-interest] Serious Bug when using BitSet generation-Forgot: USING ANTLR 2.7.5 !!!!

[Terence Parr]

Hi.  I'm looking into this for 2.7.6 release imminent this weekish.

First, this is a bug in your grammar right:

> commonLibraryBlock3
>  : {isCategory}? libraryDeclarations
>  | {isCategory}? ( )

that 2nd production is impossible, right?

Now, you have a rule with:

  | {isProgram}? ( )         ****************   NOTE : These kind of  
empty productions FAIL to match an empty Production when using BITSET  
generation !
  | {isCategory}? ( )
  | {isConstants}?   ( )

Now.  "( )" is not necessary, so remove those; extra code is  
generated I think.

Your intent is to have an if-then-else chain with predicates tested,  
right?  ANTLR should remove all lookahead for the last n-1  
productions as the lookahead clearly is the FOLLOW(your rule) and  
therefore identical for all n productions.  I'm stunned there is any  
lookahead even with no bitsets.  ANTLR should delete all lookahead  
for 2..n-1 productions.  Seems to me it's a bug that it *does* work  
without bitsets.  I'm making an example.

Ter