encoding/json: permit encoding uintptr as a string

Fixes #22629

Change-Id: I31e85f9faa125ee0dfd6d3c5fa89334b00d61e6e
Reviewed-on: https://go-review.googlesource.com/76530
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>
Reviewed-by: Joe Tsai <joetsai@google.com>

src/encoding/json/decode_test.go

@@ -1194,6 +1194,7 @@ type All struct {
 	Foo2 string `json:"bar2,dummyopt"`
 
 	IntStr     int64   `json:",string"`
+	UintptrStr uintptr `json:",string"`
 
 	PBool    *bool
 	PInt     *int
@@ -1264,6 +1265,7 @@ var allValue = All{
 	Foo:        "foo",
 	Foo2:       "foo2",
 	IntStr:     42,
+	UintptrStr: 44,
 	String:     "16",
 	Map: map[string]Small{
 		"17": {Tag: "tag17"},
@@ -1326,6 +1328,7 @@ var allValueIndent = `{
 	"bar": "foo",
 	"bar2": "foo2",
 	"IntStr": "42",
+	"UintptrStr": "44",
 	"PBool": null,
 	"PInt": null,
 	"PInt8": null,
@@ -1418,6 +1421,7 @@ var pallValueIndent = `{
 	"bar": "",
 	"bar2": "",
         "IntStr": "0",
+	"UintptrStr": "0",
 	"PBool": true,
 	"PInt": 2,
 	"PInt8": 3,

src/encoding/json/encode.go

@@ -1131,7 +1131,7 @@ func typeFields(t reflect.Type) []field {
 					switch ft.Kind() {
 					case reflect.Bool,
 						reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64,
-						reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64,
+						reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr,
 						reflect.Float32, reflect.Float64,
 						reflect.String:
 						quoted = true

src/encoding/json/encode_test.go

@@ -73,12 +73,14 @@ func TestOmitEmpty(t *testing.T) {
 type StringTag struct {
 	BoolStr    bool    `json:",string"`
 	IntStr     int64   `json:",string"`
+	UintptrStr uintptr `json:",string"`
 	StrStr     string  `json:",string"`
 }
 
 var stringTagExpected = `{
  "BoolStr": "true",
  "IntStr": "42",
+ "UintptrStr": "44",
  "StrStr": "\"xzbit\""
 }`
 
@@ -86,6 +88,7 @@ func TestStringTag(t *testing.T) {
 	var s StringTag
 	s.BoolStr = true
 	s.IntStr = 42
+	s.UintptrStr = 44
 	s.StrStr = "xzbit"
 	got, err := MarshalIndent(&s, "", " ")
 	if err != nil {