html/template: escaping {{else}} is unimplemented

[dvyukov]

The following program crashes with panic:

package main

import (
    "html/template"
    "io/ioutil"
)

func main() {
    t, err := template.New("foo").Parse(string(data))
    if err != nil {
        return
    }
    t.Execute(ioutil.Discard, nil)
}

var data = "{{else}}"

panic: escaping {{else}} is unimplemented

goroutine 1 [running]:
html/template.(*escaper).escape(0xc208010540, 0x0, 0x0, 0x7f73f1e9a2b0, 0xc20800e460, 0x700000000000000, 0x0)
    src/html/template/escape.go:133 +0x449
html/template.(*escaper).escapeList(0xc208010540, 0x0, 0x0, 0xc2080147e0, 0x0, 0x0)
    src/html/template/escape.go:440 +0x1c9
html/template.(*escaper).escapeListConditionally(0xc208010500, 0x0, 0x0, 0xc2080147e0, 0xc2080419b0, 0x0, 0x0, 0x7f73f2046000)
    src/html/template/escape.go:455 +0x4be
html/template.(*escaper).escapeTemplateBody(0xc208010500, 0x0, 0x0, 0xc208010440, 0x0, 0x0, 0x8700000000000002)
    src/html/template/escape.go:573 +0x1e2
html/template.(*escaper).computeOutCtx(0xc208010500, 0x0, 0x0, 0xc208010440, 0x0, 0x0)
    src/html/template/escape.go:534 +0xc9
html/template.(*escaper).escapeTree(0xc208010500, 0x0, 0x0, 0x7f73f1e9a2f8, 0xc2080147e0, 0x5ba240, 0x3, 0x0, 0x0, 0x0, ...)
    src/html/template/escape.go:527 +0x77f
html/template.escapeTemplate(0xc2080146f0, 0x7f73f1e9a2f8, 0xc2080147e0, 0x5ba240, 0x3, 0x0, 0x0)
    src/html/template/escape.go:23 +0x334
html/template.(*Template).escape(0xc2080146f0, 0x0, 0x0)
    src/html/template/template.go:85 +0x35d
html/template.(*Template).Execute(0xc2080146f0, 0x7f73f1e9a288, 0xc20800a4c0, 0x0, 0x0, 0x0, 0x0)
    src/html/template/template.go:101 +0x37
main.main()
    /tmp/htmltempl.go:13 +0x290

on commit ccc76db

[robpike]

The problem is in text/template, which should have rejected this template.

[gopherbot]

CL https://golang.org/cl/9620 mentions this issue.