Go target has syntax errors when MODE() is used

[peterderivaz]

With the file SimpleLexer.g4:
lexer grammar SimpleLexer;
RULE0: 'a' -> pushMode(MODE1);
mode MODE1;
RULE1: 'b' -> Mode(MODE2);
mode MODE2;
RULE2: 'c' -> popMode;

If I build using Antlr downloaded today (4.7.1)
antlr4 -Dlanguage=Go -o parser SimpleLexer.g4

The emitted code contains:
p.SetMode(MODE2)

However, p and MODE2 are not defined in the file resulting in syntax errors.

Instead, the following symbols are defined:
const (
SimpleLexerMODE1 = iota + 1
SimpleLexerMODE2
)

My guess is there is a bug in:
https://github.com/antlr/antlr4/tree/master/tool/resources/org/antlr/v4/tool/templates/codegen/Go
but I am not sure how to fix it.

Other targets (e.g. Python2 and Java) seem to work fine because MODE2 is defined in the file (instead of SimpleLexerMODE2).

For the moment I am working around this by using pushMode(MODE2) in RULE1 and popmode,popmode in RULE2.