How to debug listeners for ANTLR4 target Go

I'm trying to figure out why my listeners aren't triggering for the rules when every rule is being triggered but not the specific rules. I tested my grammar works on http://lab.antlr.org/

Thank you.

this prints...

func (f *FSLListener) EnterEveryRule(ctx antlr.ParserRuleContext) {
	fmt.Printf("EnterEveryRule %v\n", ctx.GetText())
}

but this doesn't

func (f *FSLListener) ExitVar_assignment(ctx *parser.Var_assignmentContext) error {
	fmt.Printf("Complete var assignment: %s\n", ctx.GetText())
    // ... updated this line to reflect that I was handling this error which is why I didn't see any compiler errors
    return nil 
}

Following the example listener in https://github.com/antlr/antlr4/blob/master/doc/go-target.md

My Grammar is

parser grammar fslParser;

options { tokenVocab=fslLexer; }


r: script* EOF;

script: var_assignment* init_function function_definition*;

var_assignment: VAR VALUE;
init_function: INIT cmd_list RBRACK;
function_definition: VALIDFUNCTIONID cmd_list RBRACK;

cmd_list: (cmd_expression)*;

cmd_expression:
  CMD FUNCTIONCALL
  | CMD FUNCTIONCALLWITHARGS param_list //function call
  | CMD VARREF COMMA param_list // variable reference
  | CMD builtin_functions param_list // user-defined function call
;

builtin_functions: (CREATE | DELETE | UPDATE | ADD | SUBTRACT | MULTIPLY | DIVIDE | PRINT);

param_list: ARG param (COMMA ARG param)*;
param:
  VARREF
  | VALUE
  | LETTERS VALUE
  | VARPARAM
  | VARPARAM VALUE
;

Lexer

lexer grammar fslLexer;

INIT : 'init: [' ;
VALIDFUNCTIONID : [a-zA-Z]+ ': [';
VAR : 'var' [0-9]+':' ;
VALUE : [0-9]+ ('.' [0-9]+)? ;
CMD : 'cmd:' ;
VARREF : '#var'[0-9]+ ;
FUNCTIONCALL : '#' [a-zA-Z]+ ;
FUNCTIONCALLWITHARGS : '#' [a-zA-Z]+',' ;
VARPARAM : '$' [a-zA-Z]+ ;

DIGITS: [0-9]+;
LETTERS: [a-zA-Z]+;

ARG: LETTERS DIGITS? COLON;

// Define function names as keywords
CREATE  : 'create,' ;
DELETE  : 'delete,' ;
UPDATE  : 'update,' ;
ADD     : 'add,' ;
SUBTRACT: 'subtract,' ;
MULTIPLY: 'multiply,' ;
DIVIDE  : 'divide,' ;
PRINT   : 'print,' ;

COLON : ':';
COMMA : ',';
RBRACK : ']';

SPACE : [ \t\r\n]+ -> skip ;

Example input I'm trying to match:

var1: 1
var2: 2

init: [
    cmd: #setup
]

setup: [
    cmd: #sum, id: var1, value1: #var1, value2: #var2
    cmd: #printAll
]

sum: [
   cmd: add, id: $id, operand1: $value1, operand2: $value2
]

printAll: [
   cmd: print, value: #var1
   cmd: print, value: #var2
   cmd: print, value: #var3
]

func (f *FSLListener) ExitVar_assignment(ctx *parser.Var_assignmentContext) error {
    fmt.Printf("Complete var assignment: %s\n", ctx.GetText())
}

Should be:

func (f *FSLListener) ExitVar_assignment(ctx *parser.Var_assignmentContext) {
    fmt.Printf("Complete var assignment: %s\n", ctx.GetText())
}

This is a simple syntax error in the Go code. The implementation does not have a return value. After applying this change, I can see this output:

Complete var assignment: var1:1
Complete var assignment: var2:2

And please note that the generated fslParserListener interface is:

// fslParserListener is a complete listener for a parse tree produced by fslParser.
type fslParserListener interface {
	// ExitVar_assignment is called when exiting the var_assignment production.
	ExitVar_assignment(c *Var_assignmentContext)

	// Other codes truncated
}

It does not have a return value.

To force the interface compliance, you can export the listener interface and add this statement to your code (it assumes that the interface is exported as parser.FslParserListener):

var _ parser.FslParserListener = (*FSLListener)(nil)