add Number method to enum

[timestee]

related issue: protocolbuffers/protobuf#6104 (comment)

if enum has Number method. Though we define ErrorCode in different proto files. We could solve the problem like this:

type ProtoEnum interface {
	fmt.Stringer
	Number() int32
	EnumDescriptor() ([]byte, []int)
}

func Errorf(v ProtoEnum) error {
   // now we could get the code and message desc.
}

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[dsnet]

This is fixed in v2 with the new protoreflect.Enum interface where the Number method returns a protoreflect.EnumNumber.

[timestee]

thanks @dsnet v2 is stable now ? could use it in production?

[dsnet]

It is not stable. If you're interested in tracking breaking changes, subscribe to #867.