[antlr-interest] error reporting problem in C runtime

[Davis, Alan]

I'm having a problem with error handling in the C target. In a file with multiple recognition failures on different lines, the second error is being reported with the same line number and proximity token as the first.

I think I have tracked down the problem but it seems incomprehensible that such a blatant problem would still be extant, so I'm wondering if I'm overlooking something. 

The first recognition error causes an exception object to be created and recorded in recognizer->state->exception. However I cannot find anywhere where exceptions are freed. That is, after the first exception, recognizer->state->exception is never NULL; it continues to point to the first exception indefinitely.

The second error is a token mismatch, which results in a call to recoverFromMismatchedToken(), which does:

 // Create an exception if we need one
 if (recognizer->state->exception == NULL)
    antlr3RecognitionExceptionNew(recognizer);

The predicate fails because the first exception is still there... so the constructor is not called... so the fields pinpointing the error are not set... so the second error is reported with the same source filename and line number as the first.

I was able to fix this by overriding reportError(), adding code to call freeEx() and set recognizer->state->error to NULL. But it seems like this would be part of the standard library implementation -- or at least there would be something to take care of this.

My apologies if this a known issue -- I searched the various FAQs/Wikis/groups as best as I could.

Regards, 
Alan Davis
Texas Instruments