nil pointer outputformat shortcode bug

[davidejones]

What version of Hugo are you using (hugo version)?

This is confirmed an issue with hugo 101.0 which we are currently using and also with the latest hugo 104.3.
(both extended)

Does this issue reproduce with the latest release?

Yes

What is the issue?

Under a specific set of circumstances a runtime error: invalid memory address or nil pointer dereference occurs

Full Error

View Stack Trace

ERROR 2022/10/25 09:49:02 [BUG] Got panic:
runtime error: invalid memory address or nil pointer dereference
goroutine 269 [running]:
runtime/debug.Stack()
        /usr/local/go/src/runtime/debug/stack.go:24 +0x65
github.com/gohugoio/hugo/hugolib.newPageContentOutput.func1.1()
        /root/project/hugo/hugolib/page__per_output.go:101 +0xaa
panic({0x25f2040, 0x23f09f0})
        /usr/local/go/src/runtime/panic.go:884 +0x212
github.com/gohugoio/hugo/hugolib.(*pageContentOutput).renderContent(0x0, {0xc000a83140, 0x11, 0x18}, 0x28?)
        /root/project/hugo/hugolib/page__per_output.go:636 +0x54
github.com/gohugoio/hugo/hugolib.renderShortcode(0x1, 0xc000194fc0, {{0xc00034253a, 0x2}, {{0xc0003432a0, 0x6}, {{0x2868128, 0xb}, {0x2841e13, 0x4}, ...}, ...}}, ...)
        /root/project/hugo/hugolib/shortcode.go:385 +0xd4e
github.com/gohugoio/hugo/hugolib.renderShortcode(0x0, 0xc000194fc0, {{0xc00034253a, 0x2}, {{0xc0003432a0, 0x6}, {{0x2868128, 0xb}, {0x2841e13, 0x4}, ...}, ...}}, ...)
        /root/project/hugo/hugolib/shortcode.go:368 +0xba5
github.com/gohugoio/hugo/hugolib.(*shortcodeHandler).renderShortcodesForPage(0xc00070bc70, 0xc000b57440, {{0xc0003432a0, 0x6}, {{0x2868128, 0xb}, {0x2841e13, 0x4}, {0x283d1ef, 0x1}, ...}, ...})
        /root/project/hugo/hugolib/shortcode.go:487 +0x18a
github.com/gohugoio/hugo/hugolib.newPageContentOutput.func1()
        /root/project/hugo/hugolib/page__per_output.go:112 +0x178
github.com/gohugoio/hugo/hugolib.newPageContentOutput.func2({0x837aa9?, 0x3?})
        /root/project/hugo/hugolib/page__per_output.go:201 +0x1b
github.com/gohugoio/hugo/lazy.(*Init).withTimeout.func1()
        /root/project/hugo/lazy/init.go:188 +0x3c
created by github.com/gohugoio/hugo/lazy.(*Init).withTimeout
        /root/project/hugo/lazy/init.go:187 +0x11e
Error: Error building site: "C:\Users\davidejones\Desktop\HUGOTEST\content\fr\tracing\visualization\trace.md:1:1": runtime error: invalid memory address or nil pointer dereference
Total in 402 ms

What specific conditions combine to lead to this error?

• Looping over pages in a custom output format that accesses the page .Content or .Plain
• Page markdown content containing a nested shortcode
• Multilanguage site

I'm certain these conditions apply because doing any one of these individually causes the problem to be resolved

• Removing the custom output format template or not calling .Content or .Plain in it causes it to work
• Removing the nested shortcode causes it to work
• disableLanguages = ['fr'] causes it to work

Recreated Example

TestNestedShortcodeCustomOutputFormat()

Add the following test to hugolib/shortcode_test.go to recreate

func TestNestedShortcodeCustomOutputFormat(t *testing.T) {
  t.Parallel()

  files := `
-- config.toml --

[outputFormats.Foobar]
baseName = "foobar"
isPlainText = true
mediaType = "application/json"
notAlternative = true

[languages.en]
languageName = "English"

[languages.en.outputs]
home = [ "HTML", "RSS", "Foobar" ]

[languages.fr]
languageName = "Français"

[[module.mounts]]
source = "content/en"
target = "content"
lang = "en"

[[module.mounts]]
source = "content/fr"
target = "content"
lang = "fr"

-- layouts/_default/list.foobar.json --
{{- $.Scratch.Add "data" slice -}}
{{- range (where .Site.AllPages "Kind" "!=" "home") -}}
  {{- $.Scratch.Add "data" (dict "content" (.Plain | truncate 10000) "type" .Type "full_url" .Permalink) -}}
{{- end -}}
{{- $.Scratch.Get "data" | jsonify -}}
-- content/en/p1.md --
---
title: "p1"
---

### More information

{{< tabs >}}
{{% tab "Test" %}}

It's a test

{{% /tab %}}
{{< /tabs >}}

-- content/fr/p2.md --
---
title: Test
---

### Plus d'informations

{{< tabs >}}
{{% tab "Test" %}}

C'est un test

{{% /tab %}}
{{< /tabs >}}

-- layouts/shortcodes/tabs.html --
<div>
<div class="tab-content">{{ .Inner }}</div>
</div>

-- layouts/shortcodes/tab.html --
<div>{{ .Inner }}</div>

-- layouts/_default/single.html --
{{ .Content }}
`

  b := NewIntegrationTestBuilder(
  	IntegrationTestConfig{
  		T:           t,
  		TxtarString: files,
  		Running:     true,
  		Verbose:     true,
  	},
  ).Build()

  b.AssertFileContent("public/fr/p2/index.html", `plus-dinformations`)

}

Error details

Debugging it seems to be that cp on p.pageOutput is nil at times

hugolib/shortcode.go

...

// Pre Hugo 0.55 this was the behaviour even for the outer-most
// shortcode.
if sc.doMarkup && (level > 0 || sc.configVersion() == 1) {
    var err error
    b, err := p.pageOutput.cp.renderContent([]byte(inner), false)
    if err != nil {
        return "", false, err
    }
    
...

For further context our site was working great and we discovered this bug when adding the output format code (which works successfully on other sites of ours)

[github-actions]

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