encoding/xml: restore Go 1.4 name space behavior

There is clearly work to do here with respect to xml name spaces,
but I don't believe the changes in this cycle are clearly correct.
The changes in this cycle have visible impact on the generated xml,
possibly breaking existing programs, and yet it's not clear that they
are the end of the story: there is still significant confusion about how
name spaces work or should work (see #9519, #9775, #8167, #7113).

I would like to wait to make breaking changes until we completely
understand what the behavior should be and can evaluate the benefit
of those breaking changes. My main concern here is that we will break
programs in Go 1.5 for the sake of name space adjustments and then
while trying to fix those other bugs we'll break programs in Go 1.6 too.
Let's wait until we know all the changes we want to make before we
decide whether or how to break existing programs.

This CL reverts:

5ae822ba encoding/xml: minor changes
bb7e6656 encoding/xml: fix xmlns= behavior
9f9d66d3 encoding/xml: fix default namespace of tags
b69ea018 encoding/xml: fix namespaces in a>b tags
3be158d6 encoding/xml: encoding name spaces correctly

and adjusts tests from

a9dddb53 encoding/xml: add more EncodeToken tests.

to expect Go 1.4 behavior.

I have confirmed that the name space parts of the test suite
as of this CL passes against the Go 1.4 encoding/xml package,
indicating that this CL successfully restores the Go 1.4 behavior.

(Other tests do not, but that's because there were some real
bug fixes in this cycle that are being kept. Specifically, the
tests that don't pass in Go 1.4 are TestMarshal's NestedAndComment
case, TestEncodeToken's encoding of newlines, and
TestSimpleUseOfEncodeToken returning an error for invalid
token types.)

I also checked that the Go 1.4 tests pass when run against
this copy of the sources.

Fixes #11841.

Change-Id: I97de06761038b40388ef6e3a55547ff43edee7cb
Reviewed-on: https://go-review.googlesource.com/12570Reviewed-by: Nigel Tao <nigeltao@golang.org>

src/encoding/xml/read_test.go

@@ -5,8 +5,6 @@
 package xml
 
 import (
-	"bytes"
-	"fmt"
 	"io"
 	"reflect"
 	"strings"
@@ -486,34 +484,6 @@ func TestUnmarshalNS(t *testing.T) {
 	}
 }
 
-func TestRoundTrip(t *testing.T) {
-	// From issue 7535
-	const s = `<ex:element xmlns:ex="http://example.com/schema"></ex:element>`
-	in := bytes.NewBufferString(s)
-	for i := 0; i < 10; i++ {
-		out := &bytes.Buffer{}
-		d := NewDecoder(in)
-		e := NewEncoder(out)
-
-		for {
-			t, err := d.Token()
-			if err == io.EOF {
-				break
-			}
-			if err != nil {
-				fmt.Println("failed:", err)
-				return
-			}
-			e.EncodeToken(t)
-		}
-		e.Flush()
-		in = out
-	}
-	if got := in.String(); got != s {
-		t.Errorf("have: %q\nwant: %q\n", got, s)
-	}
-}
-
 func TestMarshalNS(t *testing.T) {
 	dst := Tables{"hello", "world"}
 	data, err := Marshal(&dst)
@@ -637,7 +607,7 @@ func TestMarshalNSAttr(t *testing.T) {
 	if err != nil {
 		t.Fatalf("Marshal: %v", err)
 	}
-	want := `<TableAttrs><TAttr xmlns:json_1="http://golang.org/2/json/" xmlns:json="http://golang.org/json/" xmlns:_xmlfoo="http://golang.org/xmlfoo/" xmlns:_xml="http://golang.org/xml/" xmlns:furniture="http://www.w3schools.com/furniture" xmlns:html4="http://www.w3.org/TR/html4/" html4:table="hello" furniture:table="world" xml:lang="en_US" _xml:other="other1" _xmlfoo:other="other2" json:other="other3" json_1:other="other4"></TAttr></TableAttrs>`
+	want := `<TableAttrs><TAttr xmlns:html4="http://www.w3.org/TR/html4/" html4:table="hello" xmlns:furniture="http://www.w3schools.com/furniture" furniture:table="world" xml:lang="en_US" xmlns:_xml="http://golang.org/xml/" _xml:other="other1" xmlns:_xmlfoo="http://golang.org/xmlfoo/" _xmlfoo:other="other2" xmlns:json="http://golang.org/json/" json:other="other3" xmlns:json_1="http://golang.org/2/json/" json_1:other="other4"></TAttr></TableAttrs>`
 	str := string(data)
 	if str != want {
 		t.Errorf("Marshal:\nhave: %#q\nwant: %#q\n", str, want)

src/encoding/xml/typeinfo.go

@@ -194,14 +194,6 @@ func structFieldInfo(typ reflect.Type, f *reflect.StructField) (*fieldInfo, erro
 		return finfo, nil
 	}
 
-	if finfo.xmlns == "" && finfo.flags&fAttr == 0 {
-		// If it's an element no namespace specified, get the default
-		// from the XMLName of enclosing struct if possible.
-		if xmlname := lookupXMLName(typ); xmlname != nil {
-			finfo.xmlns = xmlname.xmlns
-		}
-	}
-
 	// Prepare field name and parents.
 	parents := strings.Split(tag, ">")
 	if parents[0] == "" {

src/encoding/xml/xml.go

@@ -35,24 +35,15 @@ func (e *SyntaxError) Error() string {
 	return "XML syntax error on line " + strconv.Itoa(e.Line) + ": " + e.Msg
 }
 
-// A Name represents an XML name (Local) annotated with a name space
-// identifier (Space). In tokens returned by Decoder.Token, the Space
-// identifier is given as a canonical URL, not the short prefix used in
-// the document being parsed.
-//
-// As a special case, XML namespace declarations will use the literal
-// string "xmlns" for the Space field instead of the fully resolved URL.
-// See Encoder.EncodeToken for more information on namespace encoding
-// behaviour.
+// A Name represents an XML name (Local) annotated
+// with a name space identifier (Space).
+// In tokens returned by Decoder.Token, the Space identifier
+// is given as a canonical URL, not the short prefix used
+// in the document being parsed.
 type Name struct {
 	Space, Local string
 }
 
-// isNamespace reports whether the name is a namespace-defining name.
-func (name Name) isNamespace() bool {
-	return name.Local == "xmlns" || name.Space == "xmlns"
-}
-
 // An Attr represents an attribute in an XML element (Name=Value).
 type Attr struct {
 	Name  Name
@@ -81,30 +72,6 @@ func (e StartElement) End() EndElement {
 	return EndElement{e.Name}
 }
 
-// setDefaultNamespace sets the namespace of the element
-// as the default for all elements contained within it.
-func (e *StartElement) setDefaultNamespace() {
-	if e.Name.Space == "" {
-		// If there's no namespace on the element, don't
-		// set the default. Strictly speaking this might be wrong, as
-		// we can't tell if the element had no namespace set
-		// or was just using the default namespace.
-		return
-	}
-	// Don't add a default name space if there's already one set.
-	for _, attr := range e.Attr {
-		if attr.Name.Space == "" && attr.Name.Local == "xmlns" {
-			return
-		}
-	}
-	e.Attr = append(e.Attr, Attr{
-		Name: Name{
-			Local: "xmlns",
-		},
-		Value: e.Name.Space,
-	})
-}
-
 // An EndElement represents an XML end element.
 type EndElement struct {
 	Name Name