encoding/json: add UnmarshalTypeError.Offset

Fixes #9693

Change-Id: Ibf07199729bfc883b2a7e051cafd98185f912acd
Reviewed-on: https://go-review.googlesource.com/3283
Reviewed-by: Russ Cox <rsc@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

2 files changed, 22 insertions, 21 deletions

diff --git a/src/encoding/json/decode.go b/src/encoding/json/decode.go
index 212365cede..f26a7d49f0 100644
--- a/src/encoding/json/decode.go
+++ b/src/encoding/json/decode.go
@@ -90,8 +90,9 @@ type Unmarshaler interface {
 // An UnmarshalTypeError describes a JSON value that was
 // not appropriate for a value of a specific Go type.
 type UnmarshalTypeError struct {
-	Value string       // description of JSON value - "bool", "array", "number -5"
-	Type  reflect.Type // type of Go value it could not be assigned to
+	Value  string       // description of JSON value - "bool", "array", "number -5"
+	Type   reflect.Type // type of Go value it could not be assigned to
+	Offset int64        // error occurred after reading Offset bytes
 }
 
 func (e *UnmarshalTypeError) Error() string {
@@ -377,7 +378,7 @@ func (d *decodeState) array(v reflect.Value) {
 		return
 	}
 	if ut != nil {
-		d.saveError(&UnmarshalTypeError{"array", v.Type()})
+		d.saveError(&UnmarshalTypeError{"array", v.Type(), int64(d.off)})
 		d.off--
 		d.next()
 		return
@@ -396,7 +397,7 @@ func (d *decodeState) array(v reflect.Value) {
 		// Otherwise it's invalid.
 		fallthrough
 	default:
-		d.saveError(&UnmarshalTypeError{"array", v.Type()})
+		d.saveError(&UnmarshalTypeError{"array", v.Type(), int64(d.off)})
 		d.off--
 		d.next()
 		return
@@ -485,7 +486,7 @@ func (d *decodeState) object(v reflect.Value) {
 		return
 	}
 	if ut != nil {
-		d.saveError(&UnmarshalTypeError{"object", v.Type()})
+		d.saveError(&UnmarshalTypeError{"object", v.Type(), int64(d.off)})
 		d.off--
 		d.next() // skip over { } in input
 		return
@@ -504,7 +505,7 @@ func (d *decodeState) object(v reflect.Value) {
 		// map must have string kind
 		t := v.Type()
 		if t.Key().Kind() != reflect.String {
-			d.saveError(&UnmarshalTypeError{"object", v.Type()})
+			d.saveError(&UnmarshalTypeError{"object", v.Type(), int64(d.off)})
 			d.off--
 			d.next() // skip over { } in input
 			return
@@ -515,7 +516,7 @@ func (d *decodeState) object(v reflect.Value) {
 	case reflect.Struct:
 
 	default:
-		d.saveError(&UnmarshalTypeError{"object", v.Type()})
+		d.saveError(&UnmarshalTypeError{"object", v.Type(), int64(d.off)})
 		d.off--
 		d.next() // skip over { } in input
 		return
@@ -646,7 +647,7 @@ func (d *decodeState) convertNumber(s string) (interface{}, error) {
 	}
 	f, err := strconv.ParseFloat(s, 64)
 	if err != nil {
-		return nil, &UnmarshalTypeError{"number " + s, reflect.TypeOf(0.0)}
+		return nil, &UnmarshalTypeError{"number " + s, reflect.TypeOf(0.0), int64(d.off)}
 	}
 	return f, nil
 }
@@ -679,7 +680,7 @@ func (d *decodeState) literalStore(item []byte, v reflect.Value, fromQuoted bool
 			if fromQuoted {
 				d.saveError(fmt.Errorf("json: invalid use of ,string struct tag, trying to unmarshal %q into %v", item, v.Type()))
 			} else {
-				d.saveError(&UnmarshalTypeError{"string", v.Type()})
+				d.saveError(&UnmarshalTypeError{"string", v.Type(), int64(d.off)})
 			}
 		}
 		s, ok := unquoteBytes(item)
@@ -713,7 +714,7 @@ func (d *decodeState) literalStore(item []byte, v reflect.Value, fromQuoted bool
 			if fromQuoted {
 				d.saveError(fmt.Errorf("json: invalid use of ,string struct tag, trying to unmarshal %q into %v", item, v.Type()))
 			} else {
-				d.saveError(&UnmarshalTypeError{"bool", v.Type()})
+				d.saveError(&UnmarshalTypeError{"bool", v.Type(), int64(d.off)})
 			}
 		case reflect.Bool:
 			v.SetBool(value)
@@ -721,7 +722,7 @@ func (d *decodeState) literalStore(item []byte, v reflect.Value, fromQuoted bool
 			if v.NumMethod() == 0 {
 				v.Set(reflect.ValueOf(value))
 			} else {
-				d.saveError(&UnmarshalTypeError{"bool", v.Type()})
+				d.saveError(&UnmarshalTypeError{"bool", v.Type(), int64(d.off)})
 			}
 		}
 
@@ -736,10 +737,10 @@ func (d *decodeState) literalStore(item []byte, v reflect.Value, fromQuoted bool
 		}
 		switch v.Kind() {
 		default:
-			d.saveError(&UnmarshalTypeError{"string", v.Type()})
+			d.saveError(&UnmarshalTypeError{"string", v.Type(), int64(d.off)})
 		case reflect.Slice:
 			if v.Type() != byteSliceType {
-				d.saveError(&UnmarshalTypeError{"string", v.Type()})
+				d.saveError(&UnmarshalTypeError{"string", v.Type(), int64(d.off)})
 				break
 			}
 			b := make([]byte, base64.StdEncoding.DecodedLen(len(s)))
@@ -755,7 +756,7 @@ func (d *decodeState) literalStore(item []byte, v reflect.Value, fromQuoted bool
 			if v.NumMethod() == 0 {
 				v.Set(reflect.ValueOf(string(s)))
 			} else {
-				d.saveError(&UnmarshalTypeError{"string", v.Type()})
+				d.saveError(&UnmarshalTypeError{"string", v.Type(), int64(d.off)})
 			}
 		}
 
@@ -777,7 +778,7 @@ func (d *decodeState) literalStore(item []byte, v reflect.Value, fromQuoted bool
 			if fromQuoted {
 				d.error(fmt.Errorf("json: invalid use of ,string struct tag, trying to unmarshal %q into %v", item, v.Type()))
 			} else {
-				d.error(&UnmarshalTypeError{"number", v.Type()})
+				d.error(&UnmarshalTypeError{"number", v.Type(), int64(d.off)})
 			}
 		case reflect.Interface:
 			n, err := d.convertNumber(s)
@@ -786,7 +787,7 @@ func (d *decodeState) literalStore(item []byte, v reflect.Value, fromQuoted bool
 				break
 			}
 			if v.NumMethod() != 0 {
-				d.saveError(&UnmarshalTypeError{"number", v.Type()})
+				d.saveError(&UnmarshalTypeError{"number", v.Type(), int64(d.off)})
 				break
 			}
 			v.Set(reflect.ValueOf(n))
@@ -794,7 +795,7 @@ func (d *decodeState) literalStore(item []byte, v reflect.Value, fromQuoted bool
 		case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
 			n, err := strconv.ParseInt(s, 10, 64)
 			if err != nil || v.OverflowInt(n) {
-				d.saveError(&UnmarshalTypeError{"number " + s, v.Type()})
+				d.saveError(&UnmarshalTypeError{"number " + s, v.Type(), int64(d.off)})
 				break
 			}
 			v.SetInt(n)
@@ -802,7 +803,7 @@ func (d *decodeState) literalStore(item []byte, v reflect.Value, fromQuoted bool
 		case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
 			n, err := strconv.ParseUint(s, 10, 64)
 			if err != nil || v.OverflowUint(n) {
-				d.saveError(&UnmarshalTypeError{"number " + s, v.Type()})
+				d.saveError(&UnmarshalTypeError{"number " + s, v.Type(), int64(d.off)})
 				break
 			}
 			v.SetUint(n)
@@ -810,7 +811,7 @@ func (d *decodeState) literalStore(item []byte, v reflect.Value, fromQuoted bool
 		case reflect.Float32, reflect.Float64:
 			n, err := strconv.ParseFloat(s, v.Type().Bits())
 			if err != nil || v.OverflowFloat(n) {
-				d.saveError(&UnmarshalTypeError{"number " + s, v.Type()})
+				d.saveError(&UnmarshalTypeError{"number " + s, v.Type(), int64(d.off)})
 				break
 			}
 			v.SetFloat(n)
diff --git a/src/encoding/json/decode_test.go b/src/encoding/json/decode_test.go
index 83b9d39ad6..7ecc8f4402 100644
--- a/src/encoding/json/decode_test.go
+++ b/src/encoding/json/decode_test.go
@@ -231,7 +231,7 @@ 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(interface{}), out: nil},
-	{in: `{"X": [1,2,3], "Y": 4}`, ptr: new(T), out: T{Y: 4}, err: &UnmarshalTypeError{"array", reflect.TypeOf("")}},
+	{in: `{"X": [1,2,3], "Y": 4}`, ptr: new(T), out: T{Y: 4}, err: &UnmarshalTypeError{"array", reflect.TypeOf(""), 7}},
 	{in: `{"x": 1}`, ptr: new(tx), out: tx{}},
 	{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},
@@ -411,7 +411,7 @@ var unmarshalTests = []unmarshalTest{
 	{
 		in:  `{"2009-11-10T23:00:00Z": "hello world"}`,
 		ptr: &map[time.Time]string{},
-		err: &UnmarshalTypeError{"object", reflect.TypeOf(map[time.Time]string{})},
+		err: &UnmarshalTypeError{"object", reflect.TypeOf(map[time.Time]string{}), 1},
 	},
 }