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encoding/json: Add "nonil" struct tag for json encoding of nil slices/maps #27813

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encoding/json: Add "nonil" struct tag for json encoding of nil slices/maps #27813

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40e395c
added heednull option for json encoding
pjebs Sep 22, 2018
ab41add
- change from "heednull" to "nonil"
pjebs Jan 28, 2020
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20 changes: 19 additions & 1 deletion src/encoding/json/encode.go
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Original file line number Diff line number Diff line change
Expand Up @@ -71,6 +71,11 @@ import (
// false, 0, a nil pointer, a nil interface value, and any empty array,
// slice, map, or string.
//
// The "nonil" option specifies that if the field is a slice or map
// of nil value, then the value encoded will be [] or {} respectively (instead
// of "null"). If both "nonil" and "omitempty" are present, then "nonil" is
// ignored. If the field is not a slice or map, "nonil" does nothing.
//
// As a special case, if the field tag is "-", the field is always omitted.
// Note that a field with name "-" can still be generated using the tag "-,".
//
Expand Down Expand Up @@ -656,7 +661,18 @@ FieldLoop:
e.WriteString(f.nameNonEsc)
}
opts.quoted = f.quoted
f.encoder(e, fv, opts)

if f.noNil {
if f.typ.Kind() == reflect.Slice && fv.IsNil() {
e.WriteString("[]")
} else if f.typ.Kind() == reflect.Map && fv.IsNil() {
e.WriteString("{}")
} else {
f.encoder(e, fv, opts)
}
} else {
f.encoder(e, fv, opts)
}
}
if next == '{' {
e.WriteString("{}")
Expand Down Expand Up @@ -1039,6 +1055,7 @@ type field struct {
index []int
typ reflect.Type
omitEmpty bool
noNil bool
quoted bool

encoder encoderFunc
Expand Down Expand Up @@ -1156,6 +1173,7 @@ func typeFields(t reflect.Type) []field {
index: index,
typ: ft,
omitEmpty: opts.Contains("omitempty"),
noNil: !opts.Contains("omitempty") && opts.Contains("nonil"),
quoted: quoted,
}
field.nameBytes = []byte(field.name)
Expand Down
10 changes: 9 additions & 1 deletion src/encoding/json/encode_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -41,6 +41,12 @@ type Optionals struct {

Str struct{} `json:"str"`
Sto struct{} `json:"sto,omitempty"`

Slh []string `json:"slh,nonil"`
Slb []string `json:"slb,omitempty,nonil"`

Mh map[string]interface{} `json:"mh,nonil"`
Mb map[string]interface{} `json:"mb,omitempty,nonil"`
}

var optionalsExpected = `{
Expand All @@ -52,7 +58,9 @@ var optionalsExpected = `{
"br": false,
"ur": 0,
"str": {},
"sto": {}
"sto": {},
"slh": [],
"mh": {}
}`

func TestOmitEmpty(t *testing.T) {
Expand Down