ANTLR4 giving mismatched input due to brackets being inluded in a token

Question

ANTLR 4.5 is giving me a "mismatched input 'String[]' expecting 'String'" but I don't understand why the '[]' are being included in the token.

I have stripped the grammar down to the bare minimum to show the problem:

grammar Test;    
@header
{
package parser;
}

mainClass : 'class' ID '{' 'void' 'main' '(' 'String' '[' ']' ID ')' '}' ;

ID : [a-zA-Z] [a-zA-z0-9]* ;

WS : [ \t\f\r\n]+ -> channel(HIDDEN);

The input is:

class A
{
    void main(String[] args)
}

If I use 'String []' then the input is successfully parsed.

If I print out the tokens from the parse tree then they all look like what I expect, except for 'String[]' being shown as one ID token and not 3 separate tokens.

I have tried explicitly defining the 'String', '[' and ']' tokens but the result is the same.

I just can't work out what is wrong.

Only thing that comes to my mind is that your lexer rules are fighting each other. Try to convert them into named rules, not just literal rules and try to play with the order of the rules. — Divisadero

Mike Lischke Mike Lischke · Accepted Answer · 2016-03-29T07:51:46

Try defining lexer rule for each of your tokens. I wonder how you could generate your parser with this grammar. ANTLR usually spits out a message that it cannot implicitly generate lexer tokens from literals.

ANTLR4 giving mismatched input due to brackets being inluded in a token

2 Answers