encoding/json: use slices to simplify the code

Use "slices.Equal" instead of "reflect.DeepEqual".

Replace unnecessary helper type "byIndex" with "slices.SortFunc".

No effect on benchmarks.

Change-Id: I1fb2768ea6d9db7f487408fa109343be3f1741d5
GitHub-Last-Rev: 8429bc1
GitHub-Pull-Request: #66646
Reviewed-on: https://go-review.googlesource.com/c/go/+/575715
Reviewed-by: qiu laidongfeng2 <2645477756@qq.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Carlos Amedee <carlos@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>

src/encoding/json/decode_test.go

@@ -14,6 +14,7 @@ import (
 	"math/big"
 	"net"
 	"reflect"
+	"slices"
 	"strconv"
 	"strings"
 	"testing"
@@ -1998,7 +1999,7 @@ func TestByteKind(t *testing.T) {
 	if err != nil {
 		t.Fatalf("Unmarshal error: %v", err)
 	}
-	if !reflect.DeepEqual(got, want) {
+	if !slices.Equal(got, want) {
 		t.Fatalf("Marshal/Unmarshal mismatch:\n\tgot:  %v\n\twant: %v", got, want)
 	}
 }
@@ -2017,7 +2018,7 @@ func TestSliceOfCustomByte(t *testing.T) {
 	if err != nil {
 		t.Fatalf("Unmarshal error: %v", err)
 	}
-	if !reflect.DeepEqual(got, want) {
+	if !slices.Equal(got, want) {
 		t.Fatalf("Marshal/Unmarshal mismatch:\n\tgot:  %v\n\twant: %v", got, want)
 	}
 }

src/encoding/json/encode.go

@@ -1042,25 +1042,6 @@ type field struct {
 	encoder encoderFunc
 }
 
-// byIndex sorts field by index sequence.
-type byIndex []field
-
-func (x byIndex) Len() int { return len(x) }
-
-func (x byIndex) Swap(i, j int) { x[i], x[j] = x[j], x[i] }
-
-func (x byIndex) Less(i, j int) bool {
-	for k, xik := range x[i].index {
-		if k >= len(x[j].index) {
-			return false
-		}
-		if xik != x[j].index[k] {
-			return xik < x[j].index[k]
-		}
-	}
-	return len(x[i].index) < len(x[j].index)
-}
-
 // typeFields returns a list of fields that JSON should recognize for the given type.
 // The algorithm is breadth-first search over the set of structs to include - the top struct
 // and then any reachable anonymous structs.
@@ -1195,7 +1176,7 @@ func typeFields(t reflect.Type) structFields {
 		if x[i].tag != x[j].tag {
 			return x[i].tag
 		}
-		return byIndex(x).Less(i, j)
+		return slices.Compare(x[i].index, x[j].index) == -1
 	})
 
 	// Delete all fields that are hidden by the Go rules for embedded fields,
@@ -1227,7 +1208,9 @@ func typeFields(t reflect.Type) structFields {
 	}
 
 	fields = out
-	sort.Sort(byIndex(fields))
+	slices.SortFunc(fields, func(i, j field) int {
+		return slices.Compare(i.index, j.index)
+	})
 
 	for i := range fields {
 		f := &fields[i]