Add support AppendNil method for zapcore.ArrayEncoder

[tamayika]

I'm currently using custom marshaller and noticed that zapcore.ArrayEncoder does not support to append nil value.
Please see below example.

package main

import (
	"go.uber.org/zap"
	"go.uber.org/zap/zapcore"
)

type user struct {
	name string
	age  int
}

type users []*user

func (u *user) MarshalLogObject(enc zapcore.ObjectEncoder) error {
	enc.AddString("name", u.name)
	enc.AddInt("age", u.age)
	return nil
}

func (us users) MarshalLogArray(enc zapcore.ArrayEncoder) error {
	for _, u := range us {
		enc.AppendObject(u)
	}
	return nil
}

func main() {
	logger := zap.NewExample()
	defer logger.Sync()
	var users users = []*user{
		&user{"hoge", 20},
		nil,
	}
	logger.Info("users log",
		zap.Array("users", users),
	)
}

This example crashes at enc.AddString("name", u.name).

If zapcore.ArrayEncoder has AppendNil method, I can write as below

package main

import (
	"go.uber.org/zap"
	"go.uber.org/zap/zapcore"
)

type user struct {
	name string
	age  int
}

type users []*user

func (u *user) MarshalLogObject(enc zapcore.ObjectEncoder) error {
	enc.AddString("name", u.name)
	enc.AddInt("age", u.age)
	return nil
}

func (us users) MarshalLogArray(enc zapcore.ArrayEncoder) error {
	for _, u := range us {
		if u != nil {
			enc.AppendObject(u)
		} else {
			enc.AppendNil()
		}
	}
	return nil
}

func main() {
	logger := zap.NewExample()
	defer logger.Sync()
	var users users = []*user{
		&user{"hoge", 20},
		nil,
	}
	logger.Info("users log",
		zap.Array("users", users),
	)
}

Expected log is

{"level":"info","msg":"users log","users":[{"name":"hoge","age":20},null]}

[akshayjshah]

Definitely an oversight in the zapcore package 😿

Unfortunately, adding this method to the ArrayMarshaler interface is a breaking change - it'll immediately stop all third-party implementations of ArrayMarshaler from compiling. I've added it to the 2.0 wishlist in #388, though.

Today, I know of two workarounds for this. Internally, we usually don't log null values - in your second example, you'd just skip logging nil users. If that doesn't work for you, you can use the AppendReflected method to add a nil. For JSON, serializing nil with reflection is pretty fast - it shouldn't impact performance much.

[tamayika]

Thank you for the reply.
I confirmed AppendReflected works as I expected.
I'm looking forward to 2.0 release!

[akshayjshah]

Great, glad that worked. I'm going to close this issue.

I wouldn't hold your breath waiting for a 2.0 - we're collecting issues, but we may never cut a new major version.