[golang target] Specific grammar generates code that fails to compile

[ctopher78]

Before submitting an issue to ANTLR, please check off these boxes:

• I am not submitting a question on how to use ANTLR; instead, go to antlr4-discussion google group or ask at stackoverflow
• I have done a search of the existing issues to make sure I'm not sending in a duplicate

Please include information about the expected behavior, actual behavior, and the smallest grammar or code that reproduces the behavior. If appropriate, please indicate the code generation targets such as Java, C#, ... Pointers into offending code regions are also very welcome.

Expected behavior

Go code that successfully compiles.

Actual behavior

When trying to compile Golang code from a grammar that has a mixture of non-greedy subrules and two or more "?" wildcard characters, the code fails to compile. I'm using this grammar successfully with a Python2 target.

$ go run test_parse.go test.txt 
# _/Users/ccrook/git-repos/config_parser/antlr_playground/go_parser
go_parser/test_parser.go:337: no new variables on left side of :=

Steps to reproduce the behavior

Directory structure:

├── Test.g4
├── go_parser
│   ├── Test.tokens
│   ├── TestLexer.tokens
│   ├── test_base_listener.go
│   ├── test_lexer.go
│   ├── test_listener.go
│   └── test_parser.go
├── test.txt
├── test_parse.go

Grammar:
Notice multiple "?" wildcard chars in the foo parser rule.

grammar Test;

init
  : .*? (foo .*?)+ ;

foo
  : 'A' 'B'? 'C'?
  ;

ANLTR4 command:
Note: I'm pointing to a 4.6 version of the code (compiled from source 12/6).

java -jar ../lib/antlr4-4.6-SNAPSHOT.jar -Dlanguage=Go -o go_parser Test.g4

Attempt to complile/run go code:

$ go run test_parse.go test.txt 
# _/Users/ccrook/git-repos/config_parser/antlr_playground/go_parser
go_parser/test_parser.go:337: no new variables on left side of :=

The compiled go code attempts to declare the "la_" variable multiple times:

	la_ := p.GetInterpreter().AdaptivePredict(p.GetTokenStream(), 3, p.GetParserRuleContext())

	if la_ == 1 {
		{
			p.SetState(22)
			p.Match(TestParserT__1)
		}

	}
	p.SetState(26)
	p.GetErrorHandler().Sync(p)
	la_ := p.GetInterpreter().AdaptivePredict(p.GetTokenStream(), 4, p.GetParserRuleContext())

	if la_ == 1 {
		{
			p.SetState(25)
			p.Match(TestParserT__2)
		}

	}

	return localctx
}

[ctopher78]

@pboyer - First off, thanks for all your hard work on the Golang target. I think my parsing use-case hits on some uncommon grammar edge-cases. But, I'm really excited to use ANTLR4 to solve some problems my team is facing.

I'm currently testing against ANLTR4 4.6 code, which includes fixes #1423 & #1436

[pboyer]

@syn-ful Don't worry! Thanks for the help in finding the bugs. This looks like it should fix the problem: pboyer#91

Would you mind trying it out? Otherwise I'll do it tomorrow sometime.

[ctopher78]

Thanks @pboyer - Everything is working as expected now.