[antlr-interest] Two More Bugs in ANTLRv4

[Gavin Lambert]

At 21:46 23/02/2012, Jan Finis wrote:
 >The following rule does not work:
 >expr
 >   : 'x'
 >   | e1=expr '?'
 >   | e1=expr e2=expr
 >   ;
 >
 >Error: The following sets of rules are mutually left-recursive
 >[expr]
 >
 >It seems to be the concatenation operation of two expressions
 >(last alternative). If I leave it out, it works fine.

I don't consider that a bug either.  It's basically saying that 
one possible form of expr is two exprs (which in turn can each be 
another two exprs).  With no other distinguishing tokens there's 
no way to exit that path.  So that way lies infinite recursion, 
madness, and/or Sparta.  A compiler error is the correct response.

Was this from a real usage attempt (if so, please explain more 
what you were trying), or were you just experimenting?