encoding/xml: "unexpected end element" for autoclosing tags in mixed/upper case

[quasilyte]

What version of Go are you using (go version)?

1.17

Does this issue reproduce with the latest release?

Reproducible on the tip.

What operating system and processor architecture are you using (go env)?

linux/amd64.

What did you do?

go run example.go (https://play.golang.org/p/sXRjgA-nXoT):

package main

import (
	"fmt"
	"encoding/xml"
	"strings"
)

func main() {
	const input = `<br/><BR/>`
	d := xml.NewDecoder(strings.NewReader(input))
	d.Strict = false
	d.AutoClose = xml.HTMLAutoClose
	d.Entity = xml.HTMLEntity
	for {
		tok, err := d.Token()
		fmt.Printf("%#v\n", tok)
		if err != nil {
			fmt.Printf("err: %v\n", err)
			break
		}
	}
}

What did you expect to see?

xml.StartElement{Name:xml.Name{Space:"", Local:"br"}, Attr:[]xml.Attr{}}
xml.EndElement{Name:xml.Name{Space:"", Local:"br"}}
xml.StartElement{Name:xml.Name{Space:"", Local:"BR"}, Attr:[]xml.Attr{}}
xml.EndElement{Name:xml.Name{Space:"", Local:"BR"}}
<nil>
err: EOF

Note: no syntax errors.

What did you see instead?

xml.StartElement{Name:xml.Name{Space:"", Local:"br"}, Attr:[]xml.Attr{}}
xml.EndElement{Name:xml.Name{Space:"", Local:"br"}}
xml.StartElement{Name:xml.Name{Space:"", Local:"BR"}, Attr:[]xml.Attr{}}
xml.EndElement{Name:xml.Name{Space:"", Local:"BR"}}
<nil>
err: XML syntax error on line 1: unexpected end element </BR>

[gopherbot]

Change https://golang.org/cl/364734 mentions this issue: encoding/xml: improve the test coverage, fix minor bugs

[ianlancetaylor]

Moving milestone to 1.19.