encoding/json: Unmarshal doesn't use preferred match

[go101]

What version of Go are you using (go version)?

$ go version
go version go1.17 linux/amd64

Does this issue reproduce with the latest release?

Yes

What did you do?

package main

import "encoding/json"
import "fmt"

type A struct {
	Bar string `json:"Bar"`
	//BAR string `json:"bar"`
}

var s = []byte(`{
	"Bar": "1",
	"bar": "2"
}`)

func main() {
	var a A
	_ = json.Unmarshal(s, &a)
	fmt.Println(a.Bar) // 2
}

What did you expect to see?

prints 1

What did you see instead?

prints 2

[imumesh18]

It’s because json unmarshlar is case insensitive it treats b and B as same. It’s already documented.

[codehakase]

Unmarshalling is case insensitive as described in the docs:

To unmarshal JSON into a struct, Unmarshal matches incoming object keys to the keys used by Marshal (either the struct field name or its tag), preferring an exact match but also accepting a case-insensitive match.
https://pkg.go.dev/encoding/json#Unmarshal

[seankhliao]

Duplicate of #14750