[antlr-interest] Antlr3 does not report error with incorrect input.

[Martin Fowler]

I should have also mentioned that there's no error messages appearing 
either. Even if it resynchronizes, I would expect to see some kind of 
error message. I'm not at the point where I yet need to fiddle with the 
error recovery side of things, so I'll cross that bridge later. However 
I'd like to know at least enough to craft the test so that I can detect 
if Antlr found an error.

Martin

Manu wrote:
> Martin,
> 
> I think ANTLR 3 has automatic error recovery, inserting or removing a
> token. You can disable it putting:
> 
> @rulecatch {
> }
> 
> before the catalog rule.
> 
> Regards,
> Manu
> 
> 2007/3/5, Martin Fowler <fowler at acm.org>:
>> I'm doing a simple hello-world style thing with Antlr 3 just to get it
>> going. The idea is to read text in the form of
>>
>>   item camera
>>   item laser
>>
>> where item is a keyword and I want to store all the things I read. I
>> can write a grammar that reads in the values, but the odd thing is
>> that this grammar doesn't seem to throw an exception if I put in
>> something incorrect like "xitem camera". Instead it reads the file,
>> not recognizing anything, and indicates no error. I would expect an
>> error if the file contains text that doesn't conform to the
>> grammar. Can anyone let me know where I'm goofing?
>>
>> BTW If I do this in AntlrWorks it does generate a NoViableAltException.
>>
>> Gory Details
>> ============
>>
>> Here's the various files. I've looked at the tokens coming out the
>> lexer, and for "xitem item" it reports two strings, as I would
>> expect. The generated parser just looks for a token and if it isn't
>> the 'item' keyword it seems to just terminate without an error.
>>
>> I'm running this using the IntelliJ plug in.
>>
>>
>> ------------ Grammar File ----------------
>>
>> grammar Catalog;
>>
>> @header{
>> package parser;
>> import model.*;
>> }
>> @lexer::header {
>> package parser;
>> }
>>
>> @members {
>>   public Configuration result = new Configuration();
>> }
>>
>> catalog :  item*;
>>
>> item    : ITEM_DEC n=name {result.addItem(new Item ($n.text));};
>>
>> name    : STRING;
>>
>> ITEM_DEC
>>        : 'item';
>> STRING  : ('a'..'z' | 'A'..'Z')+ ;
>>
>> fragment NEWLINE:'\r' ? '\n' ;
>> WS : (' ' |'\t' | NEWLINE)+ {skip();} ;
>>
>> ------------------ Test File --------------
>>
>> import static org.junit.Assert.*;
>> import org.junit.*;
>>
>> import parser.*;
>> import model.*;
>>
>> import java.io.*;
>>
>> public class CatalogTest {
>>
>>  // This test fails
>>   @Test(expected = RuntimeException.class)
>>   public void failOnParseError() {
>>     StringReader input = new StringReader("xitem foo");
>>     Configuration config = ParserCommand.parse(input);
>>   }
>>
>> }
>>
>> ---- Command wrapper ----------------
>> package parser;
>>
>> import model.*;
>>
>> import org.antlr.runtime.*;
>>
>> import java.io.*;
>>
>> public class ParserCommand {
>>   private CatalogParser parser;
>>   private Reader input;
>>
>>   public ParserCommand(Reader input) {
>>     this.input = input;
>>   }
>>
>>   public static Configuration parse(Reader input) {
>>     ParserCommand cmd = new ParserCommand(input);
>>     cmd.run();
>>     return cmd.getConfiguration();
>>   }
>>
>>   private Configuration getConfiguration() {
>>     return parser.result;
>>   }
>>
>>   public void run() {
>>     try {
>>       CatalogLexer lexer = new CatalogLexer(new 
>> ANTLRReaderStream(input));
>>       CommonTokenStream tokens = new CommonTokenStream(lexer);
>>       for (Object t : tokens.getTokens()) System.out.printf("<%s> = ", 
>> t);
>>       parser = new CatalogParser(tokens);
>>       parser.catalog();
>>     } catch (Exception e) {
>>       throw new RuntimeException(e);
>>     }
>>   }
>>
>> }
>>
>>
>> -- 
>> Martin Fowler
>> http://martinfowler.com
>>

-- 
Martin Fowler
http://martinfowler.com