Bug: Incorrect encoding of float32 numbers

[hemantjadon]

zap.Float32 field types incorrectly formats the float32 numbers. The precision (bitSize) information is lost while converting float32.
Eg. 2.71 is formatted as 2.7100000381469727

package main

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

func main() {
    l, _ := zap.NewProduction()

    l.Info("test", zap.Float32("key", 2.71))
}

Got output

{"level":"info","ts":1257894000,"caller":"sandbox3599029287/prog.go:10","msg":"test","key":2.7100000381469727}

Expected output

{"level":"info","ts":1257894000,"caller":"sandbox3599029287/prog.go:10","msg":"test","key":2.71}

Reference

https://play.golang.org/p/3IkJONIZ_xN

[hemantjadon]

This is due to the fact, that correct bitSize information is not reaching the enc.appendFloat method, as on zapcore/json_encoder.go#L300, float32 value is being converted to a float64, and then is passed to enc.AppendFloat64, instead of being passed to enc.AppendFloat32

package main

import (
	"fmt"
	"strconv"
)

func main() {
	var f64 float64 = 2.71
	var f32 float32 = 2.71
	fmt.Println(strconv.FormatFloat(f64, 'f', -1, 64))          // 2.71
	fmt.Println(strconv.FormatFloat(float64(f32), 'f', -1, 32)) // 2.71
	fmt.Println(strconv.FormatFloat(float64(f32), 'f', -1, 64)) // 2.7100000381469727
}

Reference

https://play.golang.org/p/5_f8UMKIFMT

[abhinav]

Thanks for reporting! We'll try to have this fixed shortly.

(internal ref: GO-860)

[manjari25]

Released on v1.19.1