VerboseErrorMessagePolicy.java

package org.nohope.antlr4;

import org.antlr.v4.runtime.BailErrorStrategy;
import org.antlr.v4.runtime.FailedPredicateException;
import org.antlr.v4.runtime.InputMismatchException;
import org.antlr.v4.runtime.NoViableAltException;
import org.antlr.v4.runtime.Parser;
import org.antlr.v4.runtime.ParserRuleContext;
import org.antlr.v4.runtime.RecognitionException;
import org.antlr.v4.runtime.Token;
import org.antlr.v4.runtime.TokenStream;
import org.antlr.v4.runtime.misc.ParseCancellationException;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import javax.annotation.Nonnull;

/**
 */
public final class VerboseErrorMessagePolicy extends DefaultErrorStrategy {
    private static final Logger LOG = LoggerFactory.getLogger(ProperErrorMessagePolicy.class);
    private static final String UNKNOWN_RECOGNITION_ERROR_TYPE = "Unknown recognition error type: %s with message: %s";
    private static final String ALREADY_REPORTED_ERROR_MESSAGE = "Got an already reported error: %s";
    private static final String MISMATCHED_INPUT_ERROR_MESSAGE = "Parse error: mismatched input on line %s:%s. Got a %s but expected %s. Text: \"%s\"";
    private static final String VIABLE_ALTERNATIVE_ERROR_MESSAGE = "Parse error: can't find viable alternative at %s(line %s:%s). Rule context: %s. Text: \"%s\"";
    private static final String TOKEN_DISPLAY_FORMAT = "<%s>";
    private static final int STRING_START = 0;

    private final String originalExpression;

    public VerboseErrorMessagePolicy(String expression) {
        this.originalExpression = expression;
    }

    private static void setExceptionContext(Parser recognizer, RuntimeException e) {
        for (ParserRuleContext context = recognizer.getContext(); context != null; context = context.getParent()) {
            context.exception = (RecognitionException) e;
        }
    }

    @Override
    public void recover(Parser recognizer, RecognitionException error) {
        setExceptionContext(recognizer, error);
        LOG.debug("Get a parse exception: ", error);
        throw new ParseCancellationException(error);
    }

    @Override
    public void reportError(Parser recognizer, RecognitionException error) {
        if (inErrorRecoveryMode(recognizer)) {
            LOG.debug(String.format(ALREADY_REPORTED_ERROR_MESSAGE, error.getMessage()));
            return; // don't report spurious errors
        }
        beginErrorCondition(recognizer);
        if (error instanceof NoViableAltException) {
            reportNoViableAlternative(recognizer, (NoViableAltException) error);
        } else if (error instanceof InputMismatchException) {
            LOG.debug("Input mismatch: ", error);
            reportInputMismatch(recognizer, (InputMismatchException) error);
        } else if (error instanceof FailedPredicateException) {
            LOG.debug("Failed predicate exception: ", error);
            reportFailedPredicate(recognizer, (FailedPredicateException) error);
        } else {
            LOG.error(String.format(UNKNOWN_RECOGNITION_ERROR_TYPE, error.getClass().getName(), error.getMessage()));
            recognizer.notifyErrorListeners(error.getOffendingToken(), error.getMessage(), error);
        }
    }

    @Override
    protected void reportNoViableAlternative(@Nonnull Parser recognizer,
                                             @Nonnull NoViableAltException e) {
        String msg = formViableExceptionMessage(e, recognizer);
        LOG.debug("Got a non-viable exception {}. Original exception: ", msg, e);
        recognizer.notifyErrorListeners(e.getOffendingToken(), msg, e);
        throw new ParseCancellationException(msg, e);
    }

    private boolean tokenIsEOF(Token token) {
        return getSymbolType(token) == Token.EOF;
    }

    private static String getContext(Parser recognizer, TokenStream tokens) {
        String context = tokens.getText(recognizer.getContext());
        return context.isEmpty() ? "No context available" : context;
    }

    private String getPieceOfTextWhichContainsError(RecognitionException e) {
        return originalExpression.substring(STRING_START, e.getOffendingToken().getStopIndex());
    }

    private String formViableExceptionMessage(NoViableAltException e, Parser recognizer) {
        TokenStream tokens = recognizer.getInputStream();
        String text = getPieceOfTextWhichContainsError(e);
        String context = getContext(recognizer, tokens);
        return String.format(VIABLE_ALTERNATIVE_ERROR_MESSAGE,
                escapeWSAndQuote(getInputToken(e, tokens)),
                e.getOffendingToken().getLine(),
                e.getOffendingToken().getCharPositionInLine(),
                context, text);
    }

    @Override
    public Token recoverInline(Parser recognizer)
            throws RecognitionException {
        LOG.debug("Got an input mismatch exception");
        InputMismatchException e = new InputMismatchException(recognizer);
        setExceptionContext(recognizer, e);
        reportError(recognizer, e);
        throw e;
    }

    private static String getExpectedToken(Parser recognizer, InputMismatchException e) {
        return e.getExpectedTokens().toString(recognizer.getTokenNames());
    }

    private static int getCharPositionInLine(InputMismatchException e) {
        return e.getOffendingToken().getCharPositionInLine();
    }

    private static int getLine(InputMismatchException e) {
        return e.getOffendingToken().getLine();
    }

    private String createErrorMessage(Parser recognizer, InputMismatchException e) {
        return String.format(MISMATCHED_INPUT_ERROR_MESSAGE,
                getLine(e),
                getCharPositionInLine(e),
                getTokenErrorDisplay(e.getOffendingToken()),
                getExpectedToken(recognizer, e),
                getPieceOfTextWhichContainsError(e));
    }

    @Override
    protected void reportInputMismatch(@Nonnull Parser recognizer,
                                       @Nonnull InputMismatchException e) {
        String msg = createErrorMessage(recognizer, e);
        recognizer.notifyErrorListeners(e.getOffendingToken(), msg, e);
        throw new ParseCancellationException(msg, e);
    }

    @Override
    protected String getTokenErrorDisplay(Token token) {
        if (token == null) {
            return "<no token>";
        }
        return escapeWSAndQuote(String.format(TOKEN_DISPLAY_FORMAT, getErrorSymbol(token)));
    }

    private static boolean noTextSymbol(String s) {
        return s == null;
    }

    private String getErrorSymbol(Token token) {
        String symbol = getSymbolText(token);

        if (noTextSymbol(symbol)) {
            if (tokenIsEOF(token)) {
                symbol = "EOF";
            } else {
                symbol = String.valueOf(getSymbolType(token));
            }
        }
        return symbol;
    }

    private String getInputToken(NoViableAltException e, TokenStream tokens) {
        if (tokens != null) {
            String input;
            if (tokenIsEOF(e.getStartToken())) {
                input = "EOF";
            } else {
                input = tokens.getText(e.getStartToken(), e.getOffendingToken());
            }
            return input;
        }
        return "unknown input";
    }
}