antlr 3 bug?

[Oleg Bolshakov]

Hello. I'm using a famous instrument for generating text editor for Eclipse (Xtext). Xtext generates an antlr grammar to create parser. When working with this instrument I got some errors and started to test antlr and I found some strange thing. For the next grammar (which is a simplified version of generated one):

grammar InternalMyDsl2;

model: translation_unit;

translation_unit: (declaration ';')*;

entryRulenest_rule :    
    nest_rule
    EOF
;

nest_rule: ID?;

entryRuledeclaration:
    declaration      
    EOF
;

declaration: 'decl' nest_rule ID EOF?;

fragment LETTER : ('$'|'A'..'Z'|'a'..'z'|'_');
ID : LETTER (LETTER|'0'..'9')*;
WS : (' '|'\t'|'\r'|'\n')+;
ANY_OTHER : .;

I get the next error from antlr3.5:
>java -jar antlr-3.5-complete.jar InternalMyDsl2.g
error(202): InternalMyDsl2.g:12:12: the decision cannot distinguish between alternative(s) 1,2 for input such as "ID EOF EOF"

Why? Can anybody explain me - where are these alternatives?

[Terence Parr]

nest_rule can match ID EOF by taking ID in nest_rule OR by matching nothing and matching in declaration. This is SLL vs LL.

Ter

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[Oleg Bolshakov]

I'm very sorry. That was my mistake when posting the message.

The rule declaration was:
declaration: 'decl' nest_rule ID;


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[Oleg Bolshakov]

So the problem is that I get this message for the edited version of grammar. The two EOFs are just in entryrules and entryrules do not call (or contain) each other. I can't suppose how ID EOF EOF may be parsed