undo CL 13180043 / 318540e7857f

Accidentally submitted.

««« original CL description
encoding/json: add "overflow" struct tag option

Fixes #6213.

R=golang-dev, dsymonds, bradfitz
CC=golang-dev
https://golang.org/cl/13180043
»»»

R=golang-dev
CC=golang-dev
https://golang.org/cl/13234045

src/pkg/encoding/json/decode.go

@@ -61,10 +61,6 @@ import (
 // Instead, they are replaced by the Unicode replacement
 // character U+FFFD.
 //
-// When unmarshalling into struct values, a struct field of map type with the
-// "overflow" option will store values whose keys do not match the other struct
-// fields.
-//
 func Unmarshal(data []byte, v interface{}) error {
 	// Check for well-formedness.
 	// Avoids filling out half a data structure
@@ -493,6 +489,8 @@ func (d *decodeState) object(v reflect.Value) {
 		return
 	}
 
+	var mapElem reflect.Value
+
 	for {
 		// Read opening " of string key or closing }.
 		op := d.scanWhile(scanSkipSpace)
@@ -514,7 +512,44 @@ func (d *decodeState) object(v reflect.Value) {
 		}
 
 		// Figure out field corresponding to key.
-		subv, mapv, destring := subValue(v, key)
+		var subv reflect.Value
+		destring := false // whether the value is wrapped in a string to be decoded first
+
+		if v.Kind() == reflect.Map {
+			elemType := v.Type().Elem()
+			if !mapElem.IsValid() {
+				mapElem = reflect.New(elemType).Elem()
+			} else {
+				mapElem.Set(reflect.Zero(elemType))
+			}
+			subv = mapElem
+		} else {
+			var f *field
+			fields := cachedTypeFields(v.Type())
+			for i := range fields {
+				ff := &fields[i]
+				if ff.name == key {
+					f = ff
+					break
+				}
+				if f == nil && strings.EqualFold(ff.name, key) {
+					f = ff
+				}
+			}
+			if f != nil {
+				subv = v
+				destring = f.quoted
+				for _, i := range f.index {
+					if subv.Kind() == reflect.Ptr {
+						if subv.IsNil() {
+							subv.Set(reflect.New(subv.Type().Elem()))
+						}
+						subv = subv.Elem()
+					}
+					subv = subv.Field(i)
+				}
+			}
+		}
 
 		// Read : before value.
 		if op == scanSkipSpace {
@@ -534,9 +569,9 @@ func (d *decodeState) object(v reflect.Value) {
 
 		// Write value back to map;
 		// if using struct, subv points into struct already.
-		if mapv.IsValid() {
+		if v.Kind() == reflect.Map {
-			kv := reflect.ValueOf(key).Convert(mapv.Type().Key())
+			kv := reflect.ValueOf(key).Convert(v.Type().Key())
-			mapv.SetMapIndex(kv, subv)
+			v.SetMapIndex(kv, subv)
 		}
 
 		// Next token must be , or }.
@@ -550,57 +585,6 @@ func (d *decodeState) object(v reflect.Value) {
 	}
 }
 
-// subValue returns (and allocates, if necessary) the field in the struct or
-// map v whose name matches key.
-func subValue(v reflect.Value, key string) (subv, mapv reflect.Value, destring bool) {
-	// Create new map element.
-	if v.Kind() == reflect.Map {
-		subv = reflect.New(v.Type().Elem()).Elem()
-		mapv = v
-		return
-	}
-
-	// Get struct field.
-	var f *field
-	fields := cachedTypeFields(v.Type())
-	for i := range fields {
-		ff := &fields[i]
-		if ff.name == key {
-			f = ff
-			break
-		}
-		if f == nil && strings.EqualFold(ff.name, key) {
-			f = ff
-		}
-	}
-	if f != nil {
-		subv = fieldByIndex(v, f.index, true)
-		destring = f.quoted
-		return
-	}
-
-	// Decode into overflow field if present.
-	for _, f := range fields {
-		if f.overflow {
-			// Find overflow field.
-			mapv = fieldByIndex(v, f.index, true)
-			if k := mapv.Kind(); k != reflect.Map {
-				panic("unsupported overflow field kind: " + k.String())
-			}
-			// Make map if necessary.
-			if mapv.IsNil() {
-				mapv.Set(reflect.MakeMap(mapv.Type()))
-			}
-			// Create new map element.
-			subv = reflect.New(mapv.Type().Elem()).Elem()
-			return
-		}
-	}
-
-	// Not found.
-	return
-}
-
 // literal consumes a literal from d.data[d.off-1:], decoding into the value v.
 // The first byte of the literal has been read already
 // (that's how the caller knows it's a literal).

src/pkg/encoding/json/decode_test.go

@@ -1275,23 +1275,3 @@ func TestSkipArrayObjects(t *testing.T) {
 		t.Errorf("got error %q, want nil", err)
 	}
 }
-
-func TestDecodeOverflow(t *testing.T) {
-	json := `{"A":1,"B":2,"C":3}`
-	type S struct {
-		A int
-		E map[string]interface{} `json:",overflow"`
-		C int
-	}
-	var (
-		want = S{1, map[string]interface{}{"B": float64(2)}, 3}
-		dest S
-	)
-	err := Unmarshal([]byte(json), &dest)
-	if err != nil {
-		t.Errorf("got error %q, want nil", err)
-	}
-	if !reflect.DeepEqual(dest, want) {
-		t.Errorf("Got %+v; want %+v", dest, want)
-	}
-}

src/pkg/encoding/json/encode.go

@@ -109,10 +109,6 @@ import (
 // an anonymous struct field in both current and earlier versions, give the field
 // a JSON tag of "-".
 //
-// The "overflow" option may be used with a struct field of a map type to
-// indicate that the map contents should be marshalled as if the keys are part
-// of the struct object itself.
-//
 // Map values encode as JSON objects.
 // The map's key type must be string; the object keys are used directly
 // as map keys.
@@ -243,32 +239,6 @@ var hex = "0123456789abcdef"
 type encodeState struct {
 	bytes.Buffer // accumulated output
 	scratch      [64]byte
-	overflow     int
-}
-
-func (e *encodeState) startOverflow() {
-	e.overflow = e.Len()
-}
-
-func (e *encodeState) endOverflow() {
-	if e.overflow == 0 {
-		panic("endOverflow called before startOverflow")
-	}
-	start, end := e.overflow, e.Len()
-	b := e.Bytes()
-	if b[start] == '{' && b[end-1] == '}' {
-		// Remove surrounding { and }.
-		copy(b[start:], b[start+1:])
-		e.Truncate(end - 2)
-	} else if bytes.Equal(b[start:end], []byte("null")) {
-		// Drop "null".
-		e.Truncate(start)
-	}
-	// Remove trailing comma if overflow value was null or {}.
-	if start > 0 && e.Len() == start && b[start-1] == ',' {
-		e.Truncate(start - 1)
-	}
-	e.overflow = 0
 }
 
 // TODO(bradfitz): use a sync.Cache here
@@ -612,7 +582,7 @@ func (se *structEncoder) encode(e *encodeState, v reflect.Value, quoted bool) {
 	e.WriteByte('{')
 	first := true
 	for i, f := range se.fields {
-		fv := fieldByIndex(v, f.index, false)
+		fv := fieldByIndex(v, f.index)
 		if !fv.IsValid() || f.omitEmpty && isEmptyValue(fv) {
 			continue
 		}
@@ -621,16 +591,6 @@ func (se *structEncoder) encode(e *encodeState, v reflect.Value, quoted bool) {
 		} else {
 			e.WriteByte(',')
 		}
-		if f.overflow {
-			if tenc := se.fieldEncs[i]; tenc != nil {
-				e.startOverflow()
-				tenc(e, fv, f.quoted)
-				e.endOverflow()
-			} else {
-				panic("no encoder for " + fv.String())
-			}
-			continue
-		}
 		e.string(f.name)
 		e.WriteByte(':')
 		if tenc := se.fieldEncs[i]; tenc != nil {
@@ -650,7 +610,7 @@ func newStructEncoder(t reflect.Type, vx reflect.Value) encoderFunc {
 		fieldEncs: make([]encoderFunc, len(fields)),
 	}
 	for i, f := range fields {
-		vxf := fieldByIndex(vx, f.index, false)
+		vxf := fieldByIndex(vx, f.index)
 		if vxf.IsValid() {
 			se.fieldEncs[i] = typeEncoder(vxf.Type(), vxf)
 		}
@@ -790,16 +750,11 @@ func isValidTag(s string) bool {
 	return true
 }
 
-// fieldByIndex fetches (and allocates, if create is true) the field in v
+func fieldByIndex(v reflect.Value, index []int) reflect.Value {
-// indentified by index.
-func fieldByIndex(v reflect.Value, index []int, create bool) reflect.Value {
 	for _, i := range index {
 		if v.Kind() == reflect.Ptr {
 			if v.IsNil() {
-				if !create {
+				return reflect.Value{}
-					return reflect.Value{}
-				}
-				v.Set(reflect.New(v.Type().Elem()))
 			}
 			v = v.Elem()
 		}
@@ -971,7 +926,6 @@ type field struct {
 	typ       reflect.Type
 	omitEmpty bool
 	quoted    bool
-	overflow  bool
 }
 
 // byName sorts field by name, breaking ties with depth,
@@ -1073,15 +1027,8 @@ func typeFields(t reflect.Type) []field {
 					if name == "" {
 						name = sf.Name
 					}
-					fields = append(fields, field{
+					fields = append(fields, field{name, tagged, index, ft,
-						name:      name,
+						opts.Contains("omitempty"), opts.Contains("string")})
-						tag:       tagged,
-						index:     index,
-						typ:       ft,
-						omitEmpty: opts.Contains("omitempty"),
-						quoted:    opts.Contains("string"),
-						overflow:  opts.Contains("overflow")},
-					)
 					if count[f.typ] > 1 {
 						// If there were multiple instances, add a second,
 						// so that the annihilation code will see a duplicate.

src/pkg/encoding/json/encode_test.go

@@ -401,59 +401,3 @@ func TestStringBytes(t *testing.T) {
 		t.Errorf("encodings differ at %#q vs %#q", enc, encBytes)
 	}
 }
-
-func TestEncodeOverflow(t *testing.T) {
-	for _, c := range []struct {
-		in   interface{}
-		want string
-	}{
-		{
-			struct {
-				A int
-				E map[string]interface{} `json:",overflow"`
-				C int
-			}{
-				A: 12,
-				E: map[string]interface{}{"B": 42},
-				C: 64,
-			},
-			`{"A":12,"B":42,"C":64}`,
-		},
-		{
-			struct {
-				E map[string]interface{} `json:",overflow"`
-			}{
-				E: map[string]interface{}{"B": 42},
-			},
-			`{"B":42}`,
-		},
-		{
-			struct {
-				A int
-				E map[string]interface{} `json:",overflow"`
-			}{
-				A: 12,
-			},
-			`{"A":12}`,
-		},
-		{
-			struct {
-				A int
-				E map[string]interface{} `json:",overflow"`
-			}{
-				A: 12,
-				E: map[string]interface{}{},
-			},
-			`{"A":12}`,
-		},
-	} {
-		b, err := Marshal(c.in)
-		if err != nil {
-			t.Error(err)
-			continue
-		}
-		if got := string(b); got != c.want {
-			t.Errorf("Marshal(%q) = %s, want %s", c.in, got, c.want)
-		}
-	}
-}

src/pkg/encoding/json/example_test.go

@@ -33,29 +33,6 @@ func ExampleMarshal() {
 	// {"ID":1,"Name":"Reds","Colors":["Crimson","Red","Ruby","Maroon"]}
 }
 
-func ExampleMarshal_overflow() {
-	type Record struct {
-		ID   string
-		Seq  int
-		Meta map[string]string `json:",overflow"`
-	}
-	r := Record{
-		ID:  "CheeseWhiz",
-		Seq: 42,
-		Meta: map[string]string{
-			"Created":   "1980-06-20",
-			"Destroyed": "1998-02-06",
-		},
-	}
-	b, err := json.Marshal(r)
-	if err != nil {
-		fmt.Println("error:", err)
-	}
-	os.Stdout.Write(b)
-	// Output:
-	// {"ID":"CheeseWhiz","Seq":42,"Created":"1980-06-20","Destroyed":"1998-02-06"}
-}
-
 func ExampleUnmarshal() {
 	var jsonBlob = []byte(`[
 		{"Name": "Platypus", "Order": "Monotremata"},
@@ -75,29 +52,6 @@ func ExampleUnmarshal() {
 	// [{Name:Platypus Order:Monotremata} {Name:Quoll Order:Dasyuromorphia}]
 }
 
-func ExampleUnmarshal_overflow() {
-	var jsonBlob = []byte(`
-		{
-			"Token": "Kaip4uM1ieng6Eiw",
-			"User":  "bimmler",
-			"Animal": "rabbit"
-		}
-	`)
-	type Auth struct {
-		Token string
-		User  string
-		Extra map[string]string `json:",overflow"`
-	}
-	var auth Auth
-	err := json.Unmarshal(jsonBlob, &auth)
-	if err != nil {
-		fmt.Println("error:", err)
-	}
-	fmt.Printf("%+v", auth)
-	// Output:
-	// {Token:Kaip4uM1ieng6Eiw User:bimmler Extra:map[Animal:rabbit]}
-}
-
 // This example uses a Decoder to decode a stream of distinct JSON values.
 func ExampleDecoder() {
 	const jsonStream = `