panic when processing reflected slice field

[mhilton]

If a zap.Reflect field is provided then a reflect: call of reflect.Value.Elem on slice Value panic occurs.

For example this:

package main

import (
	"os"

	zaplogfmt "github.com/jsternberg/zap-logfmt"
	"go.uber.org/zap"
	"go.uber.org/zap/zapcore"
)

func main() {
	config := zap.NewProductionEncoderConfig()
	logger := zap.New(zapcore.NewCore(
		zaplogfmt.NewEncoder(config),
		os.Stdout,
		zapcore.DebugLevel,
	))
	logger.Info("Hello World", zap.Reflect("v", []string{"hello", "world"}))
}

produces:

panic: reflect: call of reflect.Value.Elem on slice Value

goroutine 1 [running]:
reflect.Value.Elem({0x102473c60?, 0x1400000e210?, 0x14000125898?})
	/usr/local/go/src/reflect/value.go:1259 +0x1a4
github.com/jsternberg/zap-logfmt.(*logfmtEncoder).AddReflected(0x2?, {0x10240dc7b, 0x1}, {0x102473c60?, 0x1400000e210?})
	/Users/mhilton/Library/go/pkg/mod/github.com/jsternberg/[email protected]/encoder.go:111 +0x1a0
go.uber.org/zap/zapcore.Field.AddTo({{0x10240dc7b, 0x1}, 0x17, 0x0, {0x0, 0x0}, {0x102473c60, 0x1400000e210}}, {0x1024ab358, 0x1400007ede0?})
	/Users/mhilton/Library/go/pkg/mod/go.uber.org/[email protected]/zapcore/field.go:170 +0x6d4
github.com/jsternberg/zap-logfmt.addFields(...)
	/Users/mhilton/Library/go/pkg/mod/github.com/jsternberg/[email protected]/encoder.go:537
github.com/jsternberg/zap-logfmt.(*logfmtEncoder).EncodeEntry(0x1400007ed80, {0x0, {0xc0b842abd4bf62d8, 0x11b9c4, 0x1025a8260}, {0x0, 0x0}, {0x10240f485, 0xb}, {0x0, ...}, ...}, ...)
	/Users/mhilton/Library/go/pkg/mod/github.com/jsternberg/[email protected]/encoder.go:307 +0x3b0
go.uber.org/zap/zapcore.(*ioCore).Write(0go: exit 1
x1400007edb0, {0x0, {0xc0b842abd4bf62d8, 0x11b9c4, 0x1025a8260}, {0x0, 0x0}, {0x10240f485, 0xb}, {0x0, ...}, ...}, ...)
	/Users/mhilton/Library/go/pkg/mod/go.uber.org/[email protected]/zapcore/core.go:86 +0x54
go.uber.org/zap/zapcore.(*CheckedEntry).Write(0x14000101380, {0x1400012c1c0, 0x1, 0x1})
	/Users/mhilton/Library/go/pkg/mod/go.uber.org/[email protected]/zapcore/entry.go:255 +0x150
go.uber.org/zap.(*Logger).Info(0x14000062160?, {0x10240f485?, 0x2?}, {0x1400012c1c0, 0x1, 0x1})
	/Users/mhilton/Library/go/pkg/mod/go.uber.org/[email protected]/logger.go:213 +0x54
main.main()
	/Users/mhilton/src/zap-logfmt-test/main.go:18 +0x308