How do I pretty-print productions and line numbers, using ANTLR4?

Question

I\'m trying to write a piece of code that will take an ANTLR4 parser and use it to generate ASTs for inputs similar to the ones given by the -tree option on grun (misc.Tes

Answer 1

The Trees.toStringTree method can be implemented using a ParseTreeListener. The following listener produces exactly the same output as Trees.toStringTree.

public class TreePrinterListener implements ParseTreeListener {
    private final List ruleNames;
    private final StringBuilder builder = new StringBuilder();

    public TreePrinterListener(Parser parser) {
        this.ruleNames = Arrays.asList(parser.getRuleNames());
    }

    public TreePrinterListener(List ruleNames) {
        this.ruleNames = ruleNames;
    }

    @Override
    public void visitTerminal(TerminalNode node) {
        if (builder.length() > 0) {
            builder.append(' ');
        }

        builder.append(Utils.escapeWhitespace(Trees.getNodeText(node, ruleNames), false));
    }

    @Override
    public void visitErrorNode(ErrorNode node) {
        if (builder.length() > 0) {
            builder.append(' ');
        }

        builder.append(Utils.escapeWhitespace(Trees.getNodeText(node, ruleNames), false));
    }

    @Override
    public void enterEveryRule(ParserRuleContext ctx) {
        if (builder.length() > 0) {
            builder.append(' ');
        }

        if (ctx.getChildCount() > 0) {
            builder.append('(');
        }

        int ruleIndex = ctx.getRuleIndex();
        String ruleName;
        if (ruleIndex >= 0 && ruleIndex < ruleNames.size()) {
            ruleName = ruleNames.get(ruleIndex);
        }
        else {
            ruleName = Integer.toString(ruleIndex);
        }

        builder.append(ruleName);
    }

    @Override
    public void exitEveryRule(ParserRuleContext ctx) {
        if (ctx.getChildCount() > 0) {
            builder.append(')');
        }
    }

    @Override
    public String toString() {
        return builder.toString();
    }
}

The class can be used as follows:

List ruleNames = ...;
ParseTree tree = ...;

TreePrinterListener listener = new TreePrinterListener(ruleNames);
ParseTreeWalker.DEFAULT.walk(listener, tree);
String formatted = listener.toString();

The class can be modified to produce the information in your output by updating the exitEveryRule method:

@Override
public void exitEveryRule(ParserRuleContext ctx) {
    if (ctx.getChildCount() > 0) {
        Token positionToken = ctx.getStart();
        if (positionToken != null) {
            builder.append(" [line ");
            builder.append(positionToken.getLine());
            builder.append(", offset ");
            builder.append(positionToken.getStartIndex());
            builder.append(':');
            builder.append(positionToken.getStopIndex());
            builder.append("])");
        }
        else {
            builder.append(')');
        }
    }
}