encoding/json: use reflect.TypeFor for known types

For #60088

Change-Id: I2e471c76de62944b14472966b63f5778124b9b8b
Reviewed-on: https://go-review.googlesource.com/c/go/+/514655
TryBot-Result: Gopher Robot <[email protected]>
Run-TryBot: Ian Lance Taylor <[email protected]>
Run-TryBot: Ian Lance Taylor <[email protected]>
Run-TryBot: Joseph Tsai <[email protected]>
Auto-Submit: Ian Lance Taylor <[email protected]>
Reviewed-by: Ian Lance Taylor <[email protected]>
Reviewed-by: Joseph Tsai <[email protected]>
Reviewed-by: David Chase <[email protected]>
Reviewed-by: Daniel Martí <[email protected]>

Author: ianlancetaylor

src/encoding/json/bench_test.go

@@ -450,7 +450,7 @@ func BenchmarkTypeFieldsCache(b *testing.B) {
 	// Dynamically generate many new types.
 	types := make([]reflect.Type, maxTypes)
 	fs := []reflect.StructField{{
-		Type:  reflect.TypeOf(""),
+		Type:  reflect.TypeFor[string](),
 		Index: []int{0},
 	}}
 	for i := range types {

src/encoding/json/decode.go

@@ -591,7 +591,7 @@ func (d *decodeState) array(v reflect.Value) error {
 }
 
 var nullLiteral = []byte("null")
-var textUnmarshalerType = reflect.TypeOf((*encoding.TextUnmarshaler)(nil)).Elem()
+var textUnmarshalerType = reflect.TypeFor[encoding.TextUnmarshaler]()
 
 // object consumes an object from d.data[d.off-1:], decoding into v.
 // The first byte ('{') of the object has been read already.
@@ -829,12 +829,12 @@ func (d *decodeState) convertNumber(s string) (any, error) {
 	}
 	f, err := strconv.ParseFloat(s, 64)
 	if err != nil {
-		return nil, &UnmarshalTypeError{Value: "number " + s, Type: reflect.TypeOf(0.0), Offset: int64(d.off)}
+		return nil, &UnmarshalTypeError{Value: "number " + s, Type: reflect.TypeFor[float64](), Offset: int64(d.off)}
 	}
 	return f, nil
 }
 
-var numberType = reflect.TypeOf(Number(""))
+var numberType = reflect.TypeFor[Number]()
 
 // literalStore decodes a literal stored in item into v.
 //

src/encoding/json/decode_test.go

@@ -57,7 +57,7 @@ type PP struct {
 type SS string
 
 func (*SS) UnmarshalJSON(data []byte) error {
-	return &UnmarshalTypeError{Value: "number", Type: reflect.TypeOf(SS(""))}
+	return &UnmarshalTypeError{Value: "number", Type: reflect.TypeFor[SS]()}
 }
 
 // ifaceNumAsFloat64/ifaceNumAsNumber are used to test unmarshaling with and
@@ -421,11 +421,11 @@ var unmarshalTests = []unmarshalTest{
 	{in: `"g-clef: \uD834\uDD1E"`, ptr: new(string), out: "g-clef: \U0001D11E"},
 	{in: `"invalid: \uD834x\uDD1E"`, ptr: new(string), out: "invalid: \uFFFDx\uFFFD"},
 	{in: "null", ptr: new(any), out: nil},
-	{in: `{"X": [1,2,3], "Y": 4}`, ptr: new(T), out: T{Y: 4}, err: &UnmarshalTypeError{"array", reflect.TypeOf(""), 7, "T", "X"}},
-	{in: `{"X": 23}`, ptr: new(T), out: T{}, err: &UnmarshalTypeError{"number", reflect.TypeOf(""), 8, "T", "X"}}, {in: `{"x": 1}`, ptr: new(tx), out: tx{}},
+	{in: `{"X": [1,2,3], "Y": 4}`, ptr: new(T), out: T{Y: 4}, err: &UnmarshalTypeError{"array", reflect.TypeFor[string](), 7, "T", "X"}},
+	{in: `{"X": 23}`, ptr: new(T), out: T{}, err: &UnmarshalTypeError{"number", reflect.TypeFor[string](), 8, "T", "X"}}, {in: `{"x": 1}`, ptr: new(tx), out: tx{}},
 	{in: `{"x": 1}`, ptr: new(tx), out: tx{}},
 	{in: `{"x": 1}`, ptr: new(tx), err: fmt.Errorf("json: unknown field \"x\""), disallowUnknownFields: true},
-	{in: `{"S": 23}`, ptr: new(W), out: W{}, err: &UnmarshalTypeError{"number", reflect.TypeOf(SS("")), 0, "W", "S"}},
+	{in: `{"S": 23}`, ptr: new(W), out: W{}, err: &UnmarshalTypeError{"number", reflect.TypeFor[SS](), 0, "W", "S"}},
 	{in: `{"F1":1,"F2":2,"F3":3}`, ptr: new(V), out: V{F1: float64(1), F2: int32(2), F3: Number("3")}},
 	{in: `{"F1":1,"F2":2,"F3":3}`, ptr: new(V), out: V{F1: Number("1"), F2: int32(2), F3: Number("3")}, useNumber: true},
 	{in: `{"k1":1,"k2":"s","k3":[1,2.0,3e-3],"k4":{"kk1":"s","kk2":2}}`, ptr: new(any), out: ifaceNumAsFloat64},
@@ -545,32 +545,32 @@ var unmarshalTests = []unmarshalTest{
 	{
 		in:  `{"abc":"abc"}`,
 		ptr: new(map[int]string),
-		err: &UnmarshalTypeError{Value: "number abc", Type: reflect.TypeOf(0), Offset: 2},
+		err: &UnmarshalTypeError{Value: "number abc", Type: reflect.TypeFor[int](), Offset: 2},
 	},
 	{
 		in:  `{"256":"abc"}`,
 		ptr: new(map[uint8]string),
-		err: &UnmarshalTypeError{Value: "number 256", Type: reflect.TypeOf(uint8(0)), Offset: 2},
+		err: &UnmarshalTypeError{Value: "number 256", Type: reflect.TypeFor[uint8](), Offset: 2},
 	},
 	{
 		in:  `{"128":"abc"}`,
 		ptr: new(map[int8]string),
-		err: &UnmarshalTypeError{Value: "number 128", Type: reflect.TypeOf(int8(0)), Offset: 2},
+		err: &UnmarshalTypeError{Value: "number 128", Type: reflect.TypeFor[int8](), Offset: 2},
 	},
 	{
 		in:  `{"-1":"abc"}`,
 		ptr: new(map[uint8]string),
-		err: &UnmarshalTypeError{Value: "number -1", Type: reflect.TypeOf(uint8(0)), Offset: 2},
+		err: &UnmarshalTypeError{Value: "number -1", Type: reflect.TypeFor[uint8](), Offset: 2},
 	},
 	{
 		in:  `{"F":{"a":2,"3":4}}`,
 		ptr: new(map[string]map[int]int),
-		err: &UnmarshalTypeError{Value: "number a", Type: reflect.TypeOf(int(0)), Offset: 7},
+		err: &UnmarshalTypeError{Value: "number a", Type: reflect.TypeFor[int](), Offset: 7},
 	},
 	{
 		in:  `{"F":{"a":2,"3":4}}`,
 		ptr: new(map[string]map[uint]int),
-		err: &UnmarshalTypeError{Value: "number a", Type: reflect.TypeOf(uint(0)), Offset: 7},
+		err: &UnmarshalTypeError{Value: "number a", Type: reflect.TypeFor[uint](), Offset: 7},
 	},
 
 	// Map keys can be encoding.TextUnmarshalers.
@@ -715,12 +715,12 @@ var unmarshalTests = []unmarshalTest{
 	{
 		in:  `{"2009-11-10T23:00:00Z": "hello world"}`,
 		ptr: new(map[Point]string),
-		err: &UnmarshalTypeError{Value: "object", Type: reflect.TypeOf(map[Point]string{}), Offset: 1},
+		err: &UnmarshalTypeError{Value: "object", Type: reflect.TypeFor[map[Point]string](), Offset: 1},
 	},
 	{
 		in:  `{"asdf": "hello world"}`,
 		ptr: new(map[unmarshaler]string),
-		err: &UnmarshalTypeError{Value: "object", Type: reflect.TypeOf(map[unmarshaler]string{}), Offset: 1},
+		err: &UnmarshalTypeError{Value: "object", Type: reflect.TypeFor[map[unmarshaler]string](), Offset: 1},
 	},
 
 	// related to issue 13783.
@@ -820,7 +820,7 @@ var unmarshalTests = []unmarshalTest{
 			Value:  "string",
 			Struct: "V",
 			Field:  "V.F2",
-			Type:   reflect.TypeOf(int32(0)),
+			Type:   reflect.TypeFor[int32](),
 			Offset: 20,
 		},
 	},
@@ -831,7 +831,7 @@ var unmarshalTests = []unmarshalTest{
 			Value:  "string",
 			Struct: "V",
 			Field:  "V.F2",
-			Type:   reflect.TypeOf(int32(0)),
+			Type:   reflect.TypeFor[int32](),
 			Offset: 30,
 		},
 	},
@@ -907,24 +907,24 @@ var unmarshalTests = []unmarshalTest{
 	{
 		in:  `{"data":{"test1": "bob", "test2": 123}}`,
 		ptr: new(mapStringToStringData),
-		err: &UnmarshalTypeError{Value: "number", Type: reflect.TypeOf(""), Offset: 37, Struct: "mapStringToStringData", Field: "data"},
+		err: &UnmarshalTypeError{Value: "number", Type: reflect.TypeFor[string](), Offset: 37, Struct: "mapStringToStringData", Field: "data"},
 	},
 	{
 		in:  `{"data":{"test1": 123, "test2": "bob"}}`,
 		ptr: new(mapStringToStringData),
-		err: &UnmarshalTypeError{Value: "number", Type: reflect.TypeOf(""), Offset: 21, Struct: "mapStringToStringData", Field: "data"},
+		err: &UnmarshalTypeError{Value: "number", Type: reflect.TypeFor[string](), Offset: 21, Struct: "mapStringToStringData", Field: "data"},
 	},
 
 	// trying to decode JSON arrays or objects via TextUnmarshaler
 	{
 		in:  `[1, 2, 3]`,
 		ptr: new(MustNotUnmarshalText),
-		err: &UnmarshalTypeError{Value: "array", Type: reflect.TypeOf(&MustNotUnmarshalText{}), Offset: 1},
+		err: &UnmarshalTypeError{Value: "array", Type: reflect.TypeFor[*MustNotUnmarshalText](), Offset: 1},
 	},
 	{
 		in:  `{"foo": "bar"}`,
 		ptr: new(MustNotUnmarshalText),
-		err: &UnmarshalTypeError{Value: "object", Type: reflect.TypeOf(&MustNotUnmarshalText{}), Offset: 1},
+		err: &UnmarshalTypeError{Value: "object", Type: reflect.TypeFor[*MustNotUnmarshalText](), Offset: 1},
 	},
 	// #22369
 	{
@@ -934,7 +934,7 @@ var unmarshalTests = []unmarshalTest{
 			Value:  "string",
 			Struct: "T",
 			Field:  "PP.T.Y",
-			Type:   reflect.TypeOf(int(0)),
+			Type:   reflect.TypeFor[int](),
 			Offset: 29,
 		},
 	},
@@ -945,7 +945,7 @@ var unmarshalTests = []unmarshalTest{
 			Value:  "string",
 			Struct: "T",
 			Field:  "Ts.Y",
-			Type:   reflect.TypeOf(int(0)),
+			Type:   reflect.TypeFor[int](),
 			Offset: 29,
 		},
 	},

src/encoding/json/encode.go

@@ -371,8 +371,8 @@ func typeEncoder(t reflect.Type) encoderFunc {
 }
 
 var (
-	marshalerType     = reflect.TypeOf((*Marshaler)(nil)).Elem()
-	textMarshalerType = reflect.TypeOf((*encoding.TextMarshaler)(nil)).Elem()
+	marshalerType     = reflect.TypeFor[Marshaler]()
+	textMarshalerType = reflect.TypeFor[encoding.TextMarshaler]()
 )
 
 // newTypeEncoder constructs an encoderFunc for a type.