html/template: Incorrect append values may result in incomplete HTML output

[cuishuang]

Go version

go version devel go1.24-b2f3a427dd Fri Aug 23 00:53:47 2024 +0000 darwin/arm64

Output of go env in your module/workspace:

GO111MODULE='on'
GOARCH='arm64'
GOBIN=''
GOCACHE='/Users/xxxx/Library/Caches/go-build'
GOENV='/Users/xxxx/Library/Application Support/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='arm64'
GOHOSTOS='darwin'
GOINSECURE=''
GOMODCACHE='/Users/xxxx/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='darwin'
GOPATH='/Users/xxxx/go'
GOPRIVATE=''
GOPROXY=''
GOROOT='/Users/xxxx/go'
GOSUMDB='off'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/Users/xxxx/go/pkg/tool/darwin_arm64'
GOVCS=''
GOVERSION='devel go1.24-b2f3a427dd Fri Aug 23 00:53:47 2024 +0000'
GODEBUG=''
GOTELEMETRY='local'
GOTELEMETRYDIR='/Users/xxxx/Library/Application Support/go/telemetry'
GCCGO='gccgo'
GOARM64='v8.0'
AR='ar'
CC='clang'
CXX='clang++'
CGO_ENABLED='0'
GOMOD='/dev/null'
GOWORK=''
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
PKG_CONFIG='pkg-config'
GOGCCFLAGS='-fPIC -arch arm64 -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -ffile-prefix-map=/var/folders/9t/839s3jmj73bcgyp5x_xh3gw00000gn/T/go-build550188458=/tmp/go-build -gno-record-gcc-switches -fno-common'

What did you do?

Execute the following code:

https://go.dev/play/p/RYn3g_NWx_J

package main

import (
	"fmt"
	"html/template"
	"os"
)

type Item struct {
	X, Y, Z bool
	Name    string
}

func main() {
	tmpl := template.Must(template.New("test").Parse(`
{{range $index, $item := .Items}}
Item {{$index}}: {{$item.Name}}
{{if $item.X}}{{break}}{{end}}
<a
{{if $item.Y}}{{continue}}{{end}}
>
{{if $item.Z}}{{continue}}{{end}}
{{$item.Name}}
</a>
{{end}}
`))

	data := struct {
		Items []Item
	}{
		Items: []Item{
			{X: false, Y: false, Z: false, Name: "First"},
			{X: false, Y: true, Z: false, Name: "Second"},
			{X: false, Y: false, Z: true, Name: "Third"},
			{X: true, Y: false, Z: false, Name: "Fourth"},
			{X: false, Y: false, Z: false, Name: "Fifth"},
		},
	}

	fmt.Println("Template output:")
	err := tmpl.Execute(os.Stdout, data)
	if err != nil {
		fmt.Println("Error:", err)
	}
}

What did you see happen?

The following code will not throw an error, but will output incomplete HTML content:

Template output:


Item 0: First

<a

>

First
</a>

Item 1: Second

<a

Item 2: Third

<a

>

Item 3: Fourth

What did you expect to see?

Throwing an error.

[gabyhelp]

Related Issues and Documentation

• text/template: Unexpected assignment #56490 (closed)
• embed + text/template: "incomplete or empty template" error with directory #53751 (closed)
• html/template: incorrect js inside <script> #47616 (closed)
• html/template: Parse overrides templates with empty templates #19204 (closed)
• html/template: AddParseTree does not set root template correctly #48477
• html/template: Some characters cannot be used in the template. #65289 (closed)
• affected/package: html/template With Plugins #62052 (closed)
• affected/package: html/template #56952 (closed)
• how to print string which in slice (html/template) #34317 (closed)
• x/net/html: parser should conform current w3c specifications #23071 (closed)

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[gopherbot]

Change https://go.dev/cl/607736 mentions this issue: html/template: fix the issue of incomplete HTML output due to incorrect append values