encoding/xml: prevent omitempty from omitting non-nil pointers to empty values

There was an inconsistency between the (json encoding + documentation)
and the xml encoding implementation. Pointer to an empty value was
not being serialized (i.e simply ignored). Which had the effect of making
impossible to have a struct with a string field for which we wanted to
serialize the value ""

Fixes #5452

Change-Id: Id858701801158409be01e962d2cda843424bd22a
Reviewed-on: https://go-review.googlesource.com/15684
Reviewed-by: Russ Cox <rsc@golang.org>

diff --git a/src/encoding/xml/marshal.go b/src/encoding/xml/marshal.go
index abb078ce270986a56e4473d8829f1b52aa01832a..4fa1de040a59e120e490784e3f85455c69942fc9 100644 (file)
--- a/src/encoding/xml/marshal.go
+++ b/src/encoding/xml/marshal.go
@@ -760,14 +760,6 @@ func (p *printer) marshalStruct(tinfo *typeInfo, val reflect.Value) error {
                }
                vf := finfo.value(val)
 
-               // Dereference or skip nil pointer, interface values.
-               switch vf.Kind() {
-               case reflect.Ptr, reflect.Interface:
-                       if !vf.IsNil() {
-                               vf = vf.Elem()
-                       }
-               }
-
                switch finfo.flags & fMode {
                case fCDATA, fCharData:
                        emit := EscapeText
@@ -800,6 +792,16 @@ func (p *printer) marshalStruct(tinfo *typeInfo, val reflect.Value) error {
                                        continue
                                }
                        }
+                       // Drill into interfaces and pointers.
+                       // This can turn into an infinite loop given a cyclic chain,
+                       // but it matches the Go 1 behavior.
+                       for vf.Kind() == reflect.Interface || vf.Kind() == reflect.Ptr {
+                               if vf.IsNil() {
+                                       return nil
+                               }
+                               vf = vf.Elem()
+                       }
+
                        var scratch [64]byte
                        switch vf.Kind() {
                        case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:

diff --git a/src/encoding/xml/marshal_test.go b/src/encoding/xml/marshal_test.go
index c0c6a0cd9fb6c7cdb36019fd87770eabbbb951aa..e5cf1f6bfde3b99d8322e0f4a3e139b7dc2291e0 100644 (file)
--- a/src/encoding/xml/marshal_test.go
+++ b/src/encoding/xml/marshal_test.go
@@ -207,6 +207,7 @@ type OmitAttrTest struct {
        Bool  bool    `xml:",attr,omitempty"`
        Str   string  `xml:",attr,omitempty"`
        Bytes []byte  `xml:",attr,omitempty"`
+       PStr  *string `xml:",attr,omitempty"`
 }
 
 type OmitFieldTest struct {
@@ -217,6 +218,7 @@ type OmitFieldTest struct {
        Bool  bool          `xml:",omitempty"`
        Str   string        `xml:",omitempty"`
        Bytes []byte        `xml:",omitempty"`
+       PStr  *string       `xml:",omitempty"`
        Ptr   *PresenceTest `xml:",omitempty"`
 }
 
@@ -377,6 +379,7 @@ var (
        nameAttr     = "Sarah"
        ageAttr      = uint(12)
        contentsAttr = "lorem ipsum"
+       empty = ""
 )
 
 // Unless explicitly stated as such (or *Plain), all of the
@@ -835,9 +838,10 @@ var marshalTests = []struct {
                        Bool:  true,
                        Str:   "str",
                        Bytes: []byte("byt"),
+                       PStr:  &empty,
                },
                ExpectXML: `<OmitAttrTest Int="8" int="9" Float="23.5" Uint8="255"` +
-                       ` Bool="true" Str="str" Bytes="byt"></OmitAttrTest>`,
+                       ` Bool="true" Str="str" Bytes="byt" PStr=""></OmitAttrTest>`,
        },
        {
                Value:     &OmitAttrTest{},
@@ -868,6 +872,7 @@ var marshalTests = []struct {
                        Bool:  true,
                        Str:   "str",
                        Bytes: []byte("byt"),
+                       PStr:   &empty,
                        Ptr:   &PresenceTest{},
                },
                ExpectXML: `<OmitFieldTest>` +
@@ -878,6 +883,7 @@ var marshalTests = []struct {
                        `<Bool>true</Bool>` +
                        `<Str>str</Str>` +
                        `<Bytes>byt</Bytes>` +
+                       `<PStr></PStr>` +
                        `<Ptr></Ptr>` +
                        `</OmitFieldTest>`,
        },