ANTLR Making Negative Test Cases

Question

I'm new to ANTLR and am trying to understand how to do some things with it. I need it to throw an error when a statement is missing things, like a semicolon or an end bracket. It's been called negative test cases by the problem set that I'm working through.

For example, the below code returns true, which is correct.

val program = """
1 + 2;
"""

recognize(program)

However, this code also returns true, despite it missing the semicolon at the end. It should return false ([PARSER error at line=1]: missing ';' at '').

val program = """
1 + 2
""".trimIndent()

recognize(program)

The grammar is as follows:

program: (expression ';')* | EOF;

expression: INT PLUS INT | OPENBRAC INT PLUS INT CLOSEBRAC | QUOTE IDENT QUOTE PLUS QUOTE IDENT QUOTE;

IDENT: [A-Za-z0-9]+;
INT: [-][0-9]+ | ('0'..'9')+;
PLUS: '+';
OPENBRAC: '(';
CLOSEBRAC: ')';
QUOTE: '"';

sepp2k sepp2k · Accepted Answer · 2021-03-07T20:16:08

program: (expression ';')* | EOF;

This means a program can either be zero or more instances of expression ';' followed by whatever else is in the input stream or it can be empty. Since (expression ';')* can already match the empty input by itself, the | EOF is just redundant.

What you want is program: (expression ';')* EOF, which means that a program consists of zero or more instances of expression ';', followed by the end of input, meaning there must be nothing left in the input afterwards.

ANTLR Making Negative Test Cases

1 Answers