[antlr-interest] Turning off harmless warnings

Wincent Colaiuta win at wincent.com
Fri Jun 15 02:29:46 PDT 2007


In the book (p 285) Ter writes:

"At some point ANTLR will let you silence warnings for decisions that  
ANTLR properly resolves."

Just wanted to post this to the list and ask that someone with write  
access to the bug tracker put an entry for this in there, so it  
doesn't get forgotten.

Brain-dead example rules:

   FOO : 'foo' ;
   section : element* EOF ;
   element : FOO+ ;

Here in rule "element" ANTLR doesn't know whether to match input like  
"foofoo" as a single element containing two "foo" tokens or as two  
separate elements containing just one "foo" token each. It warns  
"Decision can match input such as "FOO" using multiple alternatives:  
1, 2" and automatically resolves the ambiguity by favoring a greedy  
match in rule "element" (ie. it matches it as a single "element"  
containing two "foo" tokens).

Knowing this, you might want to be able to turn off that ambiguity  
warning so that other, more important warnings don't get overlooked  
amid the noise. I understand that ANTLR 2 had this option (either  
warnWhenFollowAmbig or generateAmbigWarnings, I don't know which). So  
like I said, it would be good if someone with write access could get  
this into the tracker, as it is not always possible to rewrite the  
rules in such a way as to eliminate all such warnings!

Cheers,
Wincent



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