no compilationUnit method found in many languages' parsers

Hi,
I'm new here and I am trying to use antlr4 for parsing some codes in my repo.
In Java or C, It works fine. I have created a listener for collecting info, such as method decl, invoke and so on.

```
Java8Parser parser = new Java8Parser(tokens);
ParseTree tree = parser.compilationUnit();

ParseTreeWalker walker = new ParseTreeWalker();
J8MethodListener listener = new J8MethodListener();
walker.walk(listener, tree);
```

But in other languages, such as go/python, I noticed that no compilationUnit method found in the parsers, which was automatically generated by g4 file.

```
GoParser parser = new GoParser(tokens);
GoMethodListener listener = new GoMethodListener();
parser. oh no
// no compilationUnit here
```

I do not know how to generate a parsetree without this method.
Thanks for your help

google mail list url: https://groups.google.com/g/antlr-discussion/c/3DSZKLBp6Qw

Start by reviewing the Java8Parser, GoParser, and Python parser entry points and the referenced ANTLR discussion thread. Determine how the grammars expose their top-level parse rules and document the correct way to build a parse tree for languages without a compilationUnit method.

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