public String getImplicitTokenLabel(String tokenName) {
		ST st = getTemplates().getInstanceOf("ImplicitTokenLabel");
		int ttype = getCodeGenerator().g.getTokenType(tokenName);
		if ( tokenName.startsWith("'") ) {
			return "s"+ttype;
		}
		String text = getTokenTypeAsTargetLabel(getCodeGenerator().g, ttype);
		st.add("tokenName", text);
		return st.render();
	}
If we know which actual function, we can provide the actual ctx type.
 This will contain implicit labels etc...  From outside, though, we
 see only ParserRuleContext unless there are externally visible stuff
 like args, locals, explicit labels, etc...
tool/src/org/antlr/v4/codegen/Target.java