text/template: Template tree produced by `template.Clone` is not in a clean state #56409

kidlj · 2022-10-25T09:07:49Z

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

$ go version
go version go1.19.2 linux/amd64

Does this issue reproduce with the latest release?

Yes.

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

go env Output

$ go env
GO111MODULE="on"
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/lijian/.cache/go-build"
GOENV="/home/lijian/.config/go/env"
GOEXE=""
GOEXPERIMENT=""
GOFLAGS="-tags=dev"
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GOMODCACHE="/home/lijian/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/home/lijian/go"
GOPRIVATE=""
GOPROXY="https://goproxy.cn,direct"
GOROOT="/usr/local/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/go/pkg/tool/linux_amd64"
GOVCS=""
GOVERSION="go1.19.2"
GCCGO="gccgo"
GOAMD64="v1"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD="/home/lijian/Code/blog/go.mod"
GOWORK=""
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -Wl,--no-gc-sections -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build3532686189=/tmp/go-build -gno-record-gcc-switches"

What did you do?

To make Go html/template inherit base template properly, every time executing an end template I make a copy via template.Clone of the full template tree, hoping it in a clean state, then add the desired end template to the cloned template tree and execute it. It almost works well, except that when a {{block "FOO" .}}{{end}} is defined in the base template, but the corresponding named block is not {{define}}-ed in the end executing template, the execution result may contain the content of block FOO defined in other templates that should not be executed.

The clone and execution process is as follows:

package templates

import (
	"embed"
	"fmt"
	"html/template"
	"io"

	"github.com/labstack/echo/v4"
)

//go:embed views/*.html
var templateFS embed.FS

type Template struct {
	templates *template.Template
}

func NewTemplate() *Template {
	templates := template.Must(template.New("").Funcs(funcMap()).ParseFS(templateFS, "views/*.html"))
	return &Template{
		templates: templates,
	}
}

func (t *Template) Render(w io.Writer, name string, data interface{}, c echo.Context) error {
	tmpl := template.Must(t.templates.Clone())
	tmpl = template.Must(tmpl.ParseFS(templateFS, fmt.Sprintf("views/%s", name)))
	return tmpl.ExecuteTemplate(w, name, data)
}

func funcMap() template.FuncMap {
	return template.FuncMap{
		"dateTime": dateTime,
		"noEscape": noEscape,
	}
}

And the base layout template is as follows:

<!DOCTYPE html>
<html lang="en">

<head>
	<meta charset="UTF-8">
	<meta http-equiv="X-UA-Compatible" content="IE=edge">
	<meta name="viewport" content="width=device-width" />
	<title>{{block "title" .}}{{end}}</title>
	<link rel="stylesheet" href="/static/bin/style.css">
	{{block "feed" .}}{{end}}
</head>

<body>
	<div class="container">
		{{block "content" .}}{{end}}
	</div>
</body>

</html>

When the blog.html template that inherits layout.html and defines block feed is executed, it works fine(that produces feed block contents):

{{template "layout.html" .}}

{{define "title"}}{{.Blog.Title}}{{end}}

{{define "feed"}}
<link rel="alternate" type="application/atom+xml" title="Blog Feed" href="{{.Feed}}">
{{end}}

{{ define "content" }}
<article>
	{{with .Blog}}
	<div class="content">
		<div class="header">
			<h2>{{.Title}}</h2>
			<span>{{.Date | dateTime}}</span>
		</div>

		{{.Content | noEscape}}
	</div>
	{{end}}
</article>
{{end}}

But when the index.html template that also inherits layout.html but does not define block feed is executed, the execution result also contains the content of block feed, which seems like come from blog.html.

{{template "layout.html" .}}

{{define "title"}}Home{{end}}

{{ define "content" }}
<article>
	<div class="content">
		<h1 class="header">Home</h1>
		<p>
			<a href="/blog/">Go to Blog →</a>
		</p>
	</div>
</article>
{{end}}

The execution result:

<!DOCTYPE html>
<html lang="en">

<head>
	<meta charset="UTF-8">
	<meta http-equiv="X-UA-Compatible" content="IE=edge">
	<meta name="viewport" content="width=device-width" />
	<title>Home</title>
	<link rel="stylesheet" href="/static/bin/style.css">
	
<!-- this line should not be produced here -->
<link rel="alternate" type="application/atom+xml" title="Blog Feed" href="">

</head>

In short, in the static blog project, I want blogs.html and blog.html to have the feed link produced, but not having it on the index.html page.

The full project code can be checked here: https://github.com/kidlj/blog

What did you expect to see?

Template tree produced by template.Clone is in a clean state that doesn't generate contents from blocks that have not been defined.

What did you see instead?

Template tree produced by template.Clone generates block contents that are defined elsewhere not being executed.

The text was updated successfully, but these errors were encountered:

heschi · 2022-10-25T16:49:07Z

cc @robpike

robpike · 2022-10-26T01:37:22Z

Does the bug occur with text/template alone? Here your test uses html/template, which is a large wrapper around text/template. It would be good to know where the problem truly arises.

kidlj · 2022-10-26T02:11:10Z

In the test project, I switched from importing html/template to text/template, the rendering result is same. So this must be a text/template issue.

robpike · 2022-10-26T02:57:59Z

Please provide a complete executable example.

kidlj · 2022-10-26T03:08:08Z

The full testing project code can be checked here: https://github.com/kidlj/blog

robpike · 2022-10-26T08:14:19Z

I'm sorry but that's a large program with 55 external dependencies, and runs as a web server.

For best results when asking for help with issues, it's best to provide a short, self-contained source file that compiles into a single binary that demonstrates the issue.

kidlj · 2022-10-26T09:04:47Z

Sure, sorry for the inconvenience. I found that I misunderstood how template parsing works while preparing a new smaller demonstration project for this issue. The truth is if the overlay template(index.html) doesn't define a named block that with the same name are defined in sibling or parent base templates, the block defined elsewhere will be executed and produce contents. This is by design.

Close.

See golang/go#56409

heschi added the NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. label Oct 25, 2022

heschi added this to the Backlog milestone Oct 25, 2022

kidlj closed this as completed Oct 26, 2022

kidlj added a commit to kidlj/miniblog that referenced this issue Oct 26, 2022

fix feed link: do not use block.

37eaf45

See golang/go#56409

golang locked and limited conversation to collaborators Oct 26, 2023

gopherbot added the FrozenDueToAge label Oct 26, 2023

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text/template: Template tree produced by `template.Clone` is not in a clean state #56409

text/template: Template tree produced by `template.Clone` is not in a clean state #56409

kidlj commented Oct 25, 2022

heschi commented Oct 25, 2022

robpike commented Oct 26, 2022

kidlj commented Oct 26, 2022

robpike commented Oct 26, 2022

kidlj commented Oct 26, 2022

robpike commented Oct 26, 2022

kidlj commented Oct 26, 2022

text/template: Template tree produced by template.Clone is not in a clean state #56409

text/template: Template tree produced by template.Clone is not in a clean state #56409

Comments

kidlj commented Oct 25, 2022

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

Does this issue reproduce with the latest release?

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

What did you do?

What did you expect to see?

What did you see instead?

heschi commented Oct 25, 2022

robpike commented Oct 26, 2022

kidlj commented Oct 26, 2022

robpike commented Oct 26, 2022

kidlj commented Oct 26, 2022

robpike commented Oct 26, 2022

kidlj commented Oct 26, 2022

text/template: Template tree produced by `template.Clone` is not in a clean state #56409

text/template: Template tree produced by `template.Clone` is not in a clean state #56409

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

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