Revert "encoding/xml: reject XML declaration after start of document"

This reverts commit 8a0fbd75a54c27ff2ae624ac2775bf752cdbceb4.

Reason for revert: Breaking real-world tests inside Google,
which means it probably breaks real-world tests outside Google.

One instance I have seen is a <!-- --> comment (often a copyright notice) before the procinst.

Another test checks that a canonicalizer can handle a test input that simply has procinsts mid-XML.

XML is full of contradictions, XML implementations more so. If we are going to start being picky, that probably needs to be controlled by a GODEBUG (and a proposal).

For #65691 (will reopen manually).

Change-Id: Ib52d0944b1478e71744a2a35b271fdf7e1c972ca
Reviewed-on: https://go-review.googlesource.com/c/go/+/570175
Reviewed-by: Than McIntosh <thanm@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Russ Cox <rsc@golang.org>

1 files changed, 0 insertions, 12 deletions

diff --git a/src/encoding/xml/xml.go b/src/encoding/xml/xml.go
index 582cfee222..0fe323f7c8 100644
--- a/src/encoding/xml/xml.go
+++ b/src/encoding/xml/xml.go
@@ -212,7 +212,6 @@ type Decoder struct {
 	line           int
 	linestart      int64
 	offset         int64
-	readNonWS      bool
 	unmarshalDepth int
 }
 
@@ -564,8 +563,6 @@ func (d *Decoder) rawToken() (Token, error) {
 		return EndElement{d.toClose}, nil
 	}
 
-	readNonWS := d.readNonWS
-
 	b, ok := d.getc()
 	if !ok {
 		return nil, d.err
@@ -578,12 +575,8 @@ func (d *Decoder) rawToken() (Token, error) {
 		if data == nil {
 			return nil, d.err
 		}
-		if !d.readNonWS && !isWhitespace(CharData(data)) {
-			d.readNonWS = true
-		}
 		return CharData(data), nil
 	}
-	d.readNonWS = true
 
 	if b, ok = d.mustgetc(); !ok {
 		return nil, d.err
@@ -634,11 +627,6 @@ func (d *Decoder) rawToken() (Token, error) {
 		data = data[0 : len(data)-2] // chop ?>
 
 		if target == "xml" {
-			if readNonWS {
-				d.err = errors.New("xml: XML declaration after start of document")
-				return nil, d.err
-			}
-
 			content := string(data)
 			ver := procInst("version", content)
 			if ver != "" && ver != "1.0" {