Is there a way to easily adapt the error messages of ANTLR4?

Question

Currenlty I\'m working on my own grammar and I would like to have specific error messages on NoViableAlternative, InputMismatch, UnwantedToke

Answer 1

After some research I came up with an another solution. In the book "The Definitive ANTLR4 Reference" in Chapter 9.4 they explain how to use error alternatives:

fcall
: ID '(' expr ')'
| ID '(' expr ')' ')' {notifyErrorListeners("Too many parentheses");}
| ID '(' expr         {notifyErrorListeners("Missing closing ')'");}
;

These error alternatives can make an ANTLR-generated parser work a little harder to choose between alternatives, but they don't in any way confuse the parser.

I adapted this to my grammar and extended the BaseErrorListener. The passed Exception to the notifyErrorListener are null (from Parser.class):

public final void notifyErrorListeners(String msg) {
    this.notifyErrorListeners(this.getCurrentToken(), msg, (RecognitionException)null);
}

So handled it in the extension of BaseErrorListener, like that:

if (recognitionException instanceof LexerNoViableAltException) {
    message = handleLexerNoViableAltException((Lexer) recognizer);
} else if (recognitionException instanceof InputMismatchException) {
    message = handleInputMismatchException((CommonToken) offendingSymbol);
} else if (recognitionException instanceof NoViableAltException) {
    message = handleNoViableAltException((CommonToken) offendingSymbol);
} else if (Objects.isNull(recognitionException)) {
// Handle Errors specified in my grammar
    message = msg;
} else {
    message = "Can't be resolved";
}

I hope that helps a little bit