Revise the fix for shortcode vs output format nilpointer

We do lazy initialization and (potentially) reuse of an output format's rendered content. We do this evaluation when we
start a new rendering a new output format. There are, however, situation where these borders gets crossed (e.g.
accessing content from another output format). We have a check for this in place for most cases, but not the content
rendering of inner markdown blocks inside shortcodes. This patch applies that same logic to the newly introduced
RenderContent method (which is not available from the templates).

Fixes #10391

7 files changed, 47 insertions, 17 deletions

diff --git a/hugolib/page.go b/hugolib/page.go
index 37bf528c7..9f0d08ca3 100644
--- a/hugolib/page.go
+++ b/hugolib/page.go
@@ -909,6 +909,7 @@ func (p *pageState) shiftToOutputFormat(isRenderingSite bool, idx int) error {
 				}
 				return cp, nil
 			})
+			p.pageOutput.contentRenderer = lcp
 			p.pageOutput.ContentProvider = lcp
 			p.pageOutput.TableOfContentsProvider = lcp
 			p.pageOutput.PageRenderProvider = lcp
diff --git a/hugolib/page__output.go b/hugolib/page__output.go
index 413323477..4ef78b612 100644
--- a/hugolib/page__output.go
+++ b/hugolib/page__output.go
@@ -81,6 +81,7 @@ type pageOutput struct {
 
 	// These interface provides the functionality that is specific for this
 	// output format.
+	contentRenderer page.ContentRenderer
 	pagePerOutputProviders
 	page.ContentProvider
 	page.TableOfContentsProvider
@@ -94,10 +95,12 @@ func (p *pageOutput) initContentProvider(cp *pageContentOutput) {
 	if cp == nil {
 		return
 	}
+	p.contentRenderer = cp
 	p.ContentProvider = cp
 	p.TableOfContentsProvider = cp
 	p.PageRenderProvider = cp
 	p.cp = cp
+
 }
 
 func (p *pageOutput) enablePlaceholders() {
diff --git a/hugolib/page__per_output.go b/hugolib/page__per_output.go
index de70047c9..e8dc69507 100644
--- a/hugolib/page__per_output.go
+++ b/hugolib/page__per_output.go
@@ -123,7 +123,7 @@ func newPageContentOutput(p *pageState, po *pageOutput) (*pageContentOutput, err
 		isHTML := cp.p.m.markup == "html"
 
 		if !isHTML {
-			r, err := cp.renderContent(cp.workContent, true)
+			r, err := po.contentRenderer.RenderContent(cp.workContent, true)
 			if err != nil {
 				return err
 			}
@@ -183,7 +183,7 @@ func newPageContentOutput(p *pageState, po *pageOutput) (*pageContentOutput, err
 				}
 			}
 		} else if cp.p.m.summary != "" {
-			b, err := cp.renderContent([]byte(cp.p.m.summary), false)
+			b, err := po.contentRenderer.RenderContent([]byte(cp.p.m.summary), false)
 			if err != nil {
 				return err
 			}
@@ -629,7 +629,7 @@ func (p *pageContentOutput) setAutoSummary() error {
 	return nil
 }
 
-func (cp *pageContentOutput) renderContent(content []byte, renderTOC bool) (converter.Result, error) {
+func (cp *pageContentOutput) RenderContent(content []byte, renderTOC bool) (converter.Result, error) {
 	if err := cp.initRenderHooks(); err != nil {
 		return nil, err
 	}
diff --git a/hugolib/shortcode.go b/hugolib/shortcode.go
index a10afe2bc..2951a1436 100644
--- a/hugolib/shortcode.go
+++ b/hugolib/shortcode.go
@@ -381,19 +381,8 @@ func renderShortcode(
 		// Pre Hugo 0.55 this was the behaviour even for the outer-most
 		// shortcode.
 		if sc.doMarkup && (level > 0 || sc.configVersion() == 1) {
-
-			cp := p.pageOutput.cp
-			if cp == nil {
-				var err error
-				cp, err = newPageContentOutput(p, p.pageOutput)
-				if err != nil {
-					return "", false, err
-				}
-				p.pageOutput.initContentProvider(cp)
-			}
-
 			var err error
-			b, err := p.pageOutput.cp.renderContent([]byte(inner), false)
+			b, err := p.pageOutput.contentRenderer.RenderContent([]byte(inner), false)
 			if err != nil {
 				return "", false, err
 			}
diff --git a/resources/page/page.go b/resources/page/page.go
index 50459c465..f9b8fdcec 100644
--- a/resources/page/page.go
+++ b/resources/page/page.go
@@ -19,6 +19,7 @@ import (
 	"html/template"
 
 	"github.com/gohugoio/hugo/identity"
+	"github.com/gohugoio/hugo/markup/converter"
 
 	"github.com/bep/gitmap"
 	"github.com/gohugoio/hugo/config"
@@ -105,6 +106,11 @@ type ContentProvider interface {
 	Len() int
 }
 
+// ContentRenderer provides the content rendering methods for some content.
+type ContentRenderer interface {
+	RenderContent(content []byte, renderTOC bool) (converter.Result, error)
+}
+
 // FileProvider provides the source file.
 type FileProvider interface {
 	File() source.File
diff --git a/resources/page/page_lazy_contentprovider.go b/resources/page/page_lazy_contentprovider.go
index ba4f8f8ef..2e4ddc352 100644
--- a/resources/page/page_lazy_contentprovider.go
+++ b/resources/page/page_lazy_contentprovider.go
@@ -17,6 +17,7 @@ import (
 	"html/template"
 
 	"github.com/gohugoio/hugo/lazy"
+	"github.com/gohugoio/hugo/markup/converter"
 )
 
 // OutputFormatContentProvider represents the method set that is "outputFormat aware" and that we
@@ -24,6 +25,14 @@ import (
 // Note that this set is currently not complete, but should cover the most common use cases.
 // For the others, the implementation will be from the page.NoopPage.
 type OutputFormatContentProvider interface {
+	OutputFormatPageContentProvider
+
+	// for internal use.
+	ContentRenderer
+}
+
+// OutputFormatPageContentProvider holds the exported methods from Page that are "outputFormat aware".
+type OutputFormatPageContentProvider interface {
 	ContentProvider
 	TableOfContentsProvider
 	PageRenderProvider
@@ -46,7 +55,7 @@ type LazyContentProvider struct {
 func NewLazyContentProvider(f func() (OutputFormatContentProvider, error)) *LazyContentProvider {
 	lcp := LazyContentProvider{
 		init: lazy.New(),
-		cp:   NopPage,
+		cp:   NopCPageContentRenderer,
 	}
 	lcp.init.Add(func() (any, error) {
 		cp, err := f()
@@ -122,3 +131,8 @@ func (lcp *LazyContentProvider) TableOfContents() template.HTML {
 	lcp.init.Do()
 	return lcp.cp.TableOfContents()
 }
+
+func (lcp *LazyContentProvider) RenderContent(content []byte, renderTOC bool) (converter.Result, error) {
+	lcp.init.Do()
+	return lcp.cp.RenderContent(content, renderTOC)
+}
diff --git a/resources/page/page_nop.go b/resources/page/page_nop.go
index cdc5fd8b1..df3227f0a 100644
--- a/resources/page/page_nop.go
+++ b/resources/page/page_nop.go
@@ -16,10 +16,12 @@
 package page
 
 import (
+	"bytes"
 	"html/template"
 	"time"
 
 	"github.com/gohugoio/hugo/identity"
+	"github.com/gohugoio/hugo/markup/converter"
 
 	"github.com/gohugoio/hugo/hugofs/files"
 	"github.com/gohugoio/hugo/tpl"
@@ -41,7 +43,15 @@ import (
 )
 
 var (
-	NopPage Page = new(nopPage)
+	NopPage                 Page            = new(nopPage)
+	NopContentRenderer      ContentRenderer = new(nopContentRenderer)
+	NopCPageContentRenderer                 = struct {
+		OutputFormatPageContentProvider
+		ContentRenderer
+	}{
+		NopPage,
+		NopContentRenderer,
+	}
 	NilPage *nopPage
 )
 
@@ -513,3 +523,10 @@ func (p *nopPage) WordCount() int {
 func (p *nopPage) GetIdentity() identity.Identity {
 	return identity.NewPathIdentity("content", "foo/bar.md")
 }
+
+type nopContentRenderer int
+
+func (r *nopContentRenderer) RenderContent(content []byte, renderTOC bool) (converter.Result, error) {
+	b := &bytes.Buffer{}
+	return b, nil
+}