encoding/xml: improve the test coverage, fix minor bugs

Improve the test coverage of encoding/xml package by adding
the test cases for the execution paths that were not covered before.

Since it reveals a couple of issues, fix them as well while we're at it.

As I used an `strings.EqualFold` instead of adding one more `strings.ToLower`,
our fix to `autoClose()` tends to run faster as well as a result.

	name             old time/op    new time/op    delta
	HTMLAutoClose-8    5.93µs ± 2%    5.75µs ± 3%  -3.16%  (p=0.000 n=10+10)
	name             old alloc/op   new alloc/op   delta
	HTMLAutoClose-8    2.60kB ± 0%    2.58kB ± 0%  -0.46%  (p=0.000 n=10+10)
	name             old allocs/op  new allocs/op  delta
	HTMLAutoClose-8      72.0 ± 0%      67.0 ± 0%  -6.94%  (p=0.000 n=10+10)

The overall `encoding/xml` test coverage increase is `88.1% -> 89.9%`;
although it may look insignificant, this CL covers some important corner cases,
like `autoClose()` functionality (that was not tested at all).

Fixes #49635
Fixes #49636

Change-Id: I50b2769896c197eb285672313b7148f4fe8bdb38
Reviewed-on: https://go-review.googlesource.com/c/go/+/364734
Trust: Bryan Mills <bcmills@google.com>
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>
Trust: Daniel Martí <mvdan@mvdan.cc>
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: Gopher Robot <gobot@golang.org>

1 files changed, 3 insertions, 7 deletions

diff --git a/src/encoding/xml/xml.go b/src/encoding/xml/xml.go
index 8a0a9c253a..ef51252dcb 100644
--- a/src/encoding/xml/xml.go
+++ b/src/encoding/xml/xml.go
@@ -10,9 +10,6 @@ package xml
 //    Annotated XML spec: https://www.xml.com/axml/testaxml.htm
 //    XML name spaces: https://www.w3.org/TR/REC-xml-names/
 
-// TODO(rsc):
-//	Test error handling.
-
 import (
 	"bufio"
 	"bytes"
@@ -499,7 +496,7 @@ func (d *Decoder) popElement(t *EndElement) bool {
 		return false
 	case s.name.Space != name.Space:
 		d.err = d.syntaxError("element <" + s.name.Local + "> in space " + s.name.Space +
-			"closed by </" + name.Local + "> in space " + name.Space)
+			" closed by </" + name.Local + "> in space " + name.Space)
 		return false
 	}
 
@@ -523,12 +520,11 @@ func (d *Decoder) autoClose(t Token) (Token, bool) {
 	if d.stk == nil || d.stk.kind != stkStart {
 		return nil, false
 	}
-	name := strings.ToLower(d.stk.name.Local)
 	for _, s := range d.AutoClose {
-		if strings.ToLower(s) == name {
+		if strings.EqualFold(s, d.stk.name.Local) {
 			// This one should be auto closed if t doesn't close it.
 			et, ok := t.(EndElement)
-			if !ok || et.Name.Local != name {
+			if !ok || !strings.EqualFold(et.Name.Local, d.stk.name.Local) {
 				return EndElement{d.stk.name}, true
 			}
 			break