ANTLR4 parse tree doesn't contain rule names

Question

ANTLR4 doesn't show rule names in parse tree.

For example, 1 + 2 is printed as:

Code in main:

    std::string test = "1 + 2";
    ANTLRInputStream input(test);
    GrammarLexer lexer(&input);
    CommonTokenStream tokens(&lexer);
    GrammarParser parser(&tokens);

    auto *tree = parser.expression();

    std::cout << tree->toStringTree(true) << "\n";

Answer 1

I dived into ANTLR's C++ runtime source code and found these 2 functions:

/// Print out a whole tree, not just a node, in LISP format
/// {@code (root child1 .. childN)}. Print just a node if this is a leaf.
virtual std::string toStringTree(bool pretty = false) = 0;

/// Specialize toStringTree so that it can print out more information
/// based upon the parser.
virtual std::string toStringTree(Parser *parser, bool pretty = false) = 0;

So, to fix the "error", replace

tree->toStringTree(true)

with

tree->toStringTree(&parser, true)