Add render template hooks for headings

This commit also

* Renames previous types to be non-specific. (e.g. hookedRenderer rather
  than linkRenderer)

Resolves #6713

3 files changed, 36 insertions, 24 deletions

diff --git a/hugolib/page.go b/hugolib/page.go
index fddc25fa0..bd518c1e1 100644
--- a/hugolib/page.go
+++ b/hugolib/page.go
@@ -375,48 +375,54 @@ func (ps *pageState) initCommonProviders(pp pagePaths) error {
 	return nil
 }
 
-func (p *pageState) createRenderHooks(f output.Format) (*hooks.Render, error) {
-
+func (p *pageState) createRenderHooks(f output.Format) (*hooks.Renderers, error) {
 	layoutDescriptor := p.getLayoutDescriptor()
 	layoutDescriptor.RenderingHook = true
 	layoutDescriptor.LayoutOverride = false
 	layoutDescriptor.Layout = ""
 
+	var renderers hooks.Renderers
+
 	layoutDescriptor.Kind = "render-link"
-	linkTempl, linkTemplFound, err := p.s.Tmpl().LookupLayout(layoutDescriptor, f)
+	templ, templFound, err := p.s.Tmpl().LookupLayout(layoutDescriptor, f)
 	if err != nil {
 		return nil, err
 	}
+	if templFound {
+		renderers.LinkRenderer = hookRenderer{
+			templateHandler: p.s.Tmpl(),
+			Provider:        templ.(tpl.Info),
+			templ:           templ,
+		}
+	}
 
 	layoutDescriptor.Kind = "render-image"
-	imgTempl, imgTemplFound, err := p.s.Tmpl().LookupLayout(layoutDescriptor, f)
+	templ, templFound, err = p.s.Tmpl().LookupLayout(layoutDescriptor, f)
 	if err != nil {
 		return nil, err
 	}
-
-	var linkRenderer hooks.LinkRenderer
-	var imageRenderer hooks.LinkRenderer
-
-	if linkTemplFound {
-		linkRenderer = contentLinkRenderer{
+	if templFound {
+		renderers.ImageRenderer = hookRenderer{
 			templateHandler: p.s.Tmpl(),
-			Provider:        linkTempl.(tpl.Info),
-			templ:           linkTempl,
+			Provider:        templ.(tpl.Info),
+			templ:           templ,
 		}
 	}
 
-	if imgTemplFound {
-		imageRenderer = contentLinkRenderer{
+	layoutDescriptor.Kind = "render-heading"
+	templ, templFound, err = p.s.Tmpl().LookupLayout(layoutDescriptor, f)
+	if err != nil {
+		return nil, err
+	}
+	if templFound {
+		renderers.HeadingRenderer = hookRenderer{
 			templateHandler: p.s.Tmpl(),
-			Provider:        imgTempl.(tpl.Info),
-			templ:           imgTempl,
+			Provider:        templ.(tpl.Info),
+			templ:           templ,
 		}
 	}
 
-	return &hooks.Render{
-		LinkRenderer:  linkRenderer,
-		ImageRenderer: imageRenderer,
-	}, nil
+	return &renderers, nil
 }
 
 func (p *pageState) getLayoutDescriptor() output.LayoutDescriptor {
diff --git a/hugolib/page__per_output.go b/hugolib/page__per_output.go
index d7841f178..77a01801d 100644
--- a/hugolib/page__per_output.go
+++ b/hugolib/page__per_output.go
@@ -245,7 +245,7 @@ type pageContentOutput struct {
 	placeholdersEnabledInit sync.Once
 
 	// May be nil.
-	renderHooks *hooks.Render
+	renderHooks *hooks.Renderers
 	// Set if there are more than one output format variant
 	renderHooksHaveVariants bool // TODO(bep) reimplement this in another way, consolidate with shortcodes
 
diff --git a/hugolib/site.go b/hugolib/site.go
index 5688b5fac..34671443e 100644
--- a/hugolib/site.go
+++ b/hugolib/site.go
@@ -1650,14 +1650,20 @@ var infoOnMissingLayout = map[string]bool{
 	"404": true,
 }
 
-type contentLinkRenderer struct {
+// hookRenderer is the canonical implementation of all hooks.ITEMRenderer,
+// where ITEM is the thing being hooked.
+type hookRenderer struct {
 	templateHandler tpl.TemplateHandler
 	identity.Provider
 	templ tpl.Template
 }
 
-func (r contentLinkRenderer) Render(w io.Writer, ctx hooks.LinkContext) error {
-	return r.templateHandler.Execute(r.templ, w, ctx)
+func (hr hookRenderer) RenderLink(w io.Writer, ctx hooks.LinkContext) error {
+	return hr.templateHandler.Execute(hr.templ, w, ctx)
+}
+
+func (hr hookRenderer) RenderHeading(w io.Writer, ctx hooks.HeadingContext) error {
+	return hr.templateHandler.Execute(hr.templ, w, ctx)
 }
 
 func (s *Site) renderForTemplate(name, outputFormat string, d interface{}, w io.Writer, templ tpl.Template) (err error) {