ANTLR How to get specific error message when using 2 alternatives in a start rule - antlr3

Question

I am trying to parse a file that can contain either a table creation script or index creation script.
Below is the grammar. When I run scripts rule with some junk input create xyz table
I get an error as line 1:0 no viable alternative at input 'create'
However when I run table_script or index_script i get specific error message as line 1:8 missing 'table' at 'xxxtab'
Is it possible to get the same error message even when I run scripts as missing table or index...?
grammar DBScript;
options { output=AST; }
tokens {
CREATE;
TABLE;
INDEX;
}
scripts
:
index_script | table_script
;
index_script
: create index index_name;
table_script
: create table table_name ;
create
: 'create';
table
: 'table';
index
: 'index';
table_name
:
IDENT;
index_name
:
IDENT;
fragment LETTER : ('a'..'z' | 'A'..'Z') ;
fragment DIGIT : '0'..'9';
INTEGER : DIGIT+ ;
IDENT : LETTER (LETTER | DIGIT)*;
WS : (' ' | '\t' | '\n' | '\r' | '\f')+ {$channel = HIDDEN;};

Answer 1

I believe that starting in ANTLR 3.5 the error message is might be more specific. However, there is no perfect way to report errors for all types of errors. The best tip I can give is telling you that ANTLR is best at reporting (and recovering from) errors appearing in LL(1) decisions, which you can write by left-factoring rules with longer lookahead requirements.
For the example above, you can left factor the reference to create as follows. Notice that neither index_script nor table_script directly reference create after the left-factoring.
scripts : create_script;
create_script : create (index_script | table_script);
index_script : index index_name;
table_script : table table_name;