zapslog: Handler should not output groups for an empty Record

[arukiidou]

• part of zapslog.Handler: Test with slogtest, fix all failures #1334

Describe the bug

slogtest cause errors:

unexpected key "H": a Handler should not output groups for an empty Record (zap/exp/zapslog/slogtest.go:165)

actual logs:

zap\exp\zapslog\logger.go:130: 2024-01-28T01:08:54.927+0900	INFO	msg	{"a": "b", "G": {"c": "d", "H": {}}}

To Reproduce
run slogtest

f: func(l *slog.Logger) {
	l.With("a", "b").WithGroup("G").With("c", "d").WithGroup("H").Info("msg")
},

Expected behavior

so that:

zap\exp\zapslog\logger.go:130: 2024-01-28T01:08:54.927+0900	INFO	msg	{"a": "b", "G": {"c": "d"}}

Additional context
none.

[arukiidou]

Solution

• When WithGroup is called, the handler "hold" the group
  • When group has not empty, "hold" is released. following:
    • With called (except slog.Attr is empty)
    • When Log called with args.
    • When LogAttrs called (except slog.Attr is empty)
  • If not, don't output the "hold" group.

[abhinav]

Resolved by #1408