Add flag to control pb struct tag omitempty

[astraw99]

Is your feature request related to a problem? Please describe.
In the code, the omitempty tag is hard-coded:

protobuf/protoc-gen-go/generator/generator.go

Line 2225 in 5d5e8c0

tag := fmt.Sprintf("protobuf:%s json:%q", g.goTag(message, field, wiretype), jsonName+",omitempty")

thus it will shadow some of zero field values, like
errCode int32 = 1, if errCode = 0 then it will not be showed in the output.

Describe the solution you'd like
Hope add tag flag like below is preferred:

message test {
 bool someone = 1 [json_omitempty=false];
}

Describe alternatives you've considered
A hack method is:

sed -i "" -e "s/,omitempty//g" ./api/proto/*.go

Obviously it is not elegant, hope pb add flag officially, thanks.

[neild]

The supported way to marshal a protobuf message as JSON is the protojson package, which follows the canonical protobuf JSON mapping.

You can use the protojson.MarshalOptions.EmitUnpopulated configuration setting to control whether zero-valued fields are emitted in the JSON encoding.

The json struct tags are deprecated. They date back to the early days of the Go protobuf implementation, before a cross-language canonical JSON mapping existed. We still generate them to avoid breaking users who depend on them, but we are no longer making any changes to these tags.

[neild]

Closing: The json: struct tags exist for backwards compatibility, but no new code should rely on them and we do not intend to add new features related to them.

[astraw99]

Got it, thanks.