Add Page.RenderShortcodes

A layouts/shortcodes/include.html shortcode may look like this:

```html
{{ $p := site.GetPage (.Get 0) }}
{{ $p.RenderShortcodes }}
```

Fixes gohugoio#7297

hugolib/page__output.go

@@ -86,6 +86,7 @@ type pageOutput struct {
 	page.ContentProvider
 	page.PageRenderProvider
 	page.TableOfContentsProvider
+	page.RenderShortcodesProvider
 
 	// May be nil.
 	cp *pageContentOutput
@@ -99,6 +100,7 @@ func (p *pageOutput) initContentProvider(cp *pageContentOutput) {
 	p.ContentProvider = cp
 	p.PageRenderProvider = cp
 	p.TableOfContentsProvider = cp
+	p.RenderShortcodesProvider = cp
 	p.cp = cp
 
 }

hugolib/page__per_output.go

@@ -350,6 +350,36 @@ func (p *pageContentOutput) Fragments(ctx context.Context) *tableofcontents.Frag
 	return p.tableOfContents
 }
 
+func (p *pageContentOutput) RenderShortcodes(ctx context.Context) (template.HTML, error) {
+	source := p.p.source.parsed.Input()
+	renderedShortcodes := p.contentPlaceholders
+	c := make([]byte, 0, len(source)+(len(source)/10))
+	for _, it := range p.p.cmap.items {
+		switch v := it.(type) {
+		case pageparser.Item:
+			c = append(c, source[v.Pos():v.Pos()+len(v.Val(source))]...)
+		case pageContentReplacement:
+			// Ignore.
+		case *shortcode:
+			// Insert the rendered shortcode.
+			renderedShortcode, found := renderedShortcodes[v.placeholder]
+			if !found {
+				// This should never happen.
+				panic(fmt.Sprintf("rendered shortcode %q not found", v.placeholder))
+			}
+			b, _, err := renderedShortcode.renderShortcode(ctx)
+			if err != nil {
+				return "", fmt.Errorf("failed to render shortcode: %w", err)
+			}
+			c = append(c, []byte(b)...)
+		default:
+			panic(fmt.Sprintf("unknown item type %T", it))
+		}
+	}
+
+	return helpers.BytesToHTML(c), nil
+}
+
 func (p *pageContentOutput) TableOfContents(ctx context.Context) template.HTML {
 	p.p.s.initInit(ctx, p.initToC, p.p)
 	return p.tableOfContentsHTML

hugolib/shortcode_test.go

@@ -1314,3 +1314,40 @@ Hello.
 	b.AssertFileContent("public/p1/index.html", "<span style=\"color:#a6e22e\">Hello.</span>")
 
 }
+
+func TestRenderShortcodes(t *testing.T) {
+	t.Parallel()
+
+	files := `
+-- config.toml --
+-- content/p1.md --
+---
+title: "p1"
+---
+# Title
+{{% include "p2" %}}
+-- content/p2.md --
+---
+title: "p2"
+---
+## Second
+{{< foo >}}
+-- layouts/shortcodes/include.html --
+{{ $p := site.GetPage (.Get 0) }}
+{{ $p.RenderShortcodes }}
+-- layouts/shortcodes/foo.html --
+Foo.
+-- layouts/_default/single.html --
+{{ .Content }}
+`
+
+	b := NewIntegrationTestBuilder(
+		IntegrationTestConfig{
+			T:           t,
+			TxtarString: files,
+		},
+	).Build()
+
+	b.AssertFileContent("public/p1/index.html", "<h1 id=\"title\">Title</h1>\n<h2 id=\"second\">Second</h2>\n<p>Foo.</p>")
+
+}

resources/page/page.go

@@ -277,6 +277,7 @@ type PageRenderProvider interface {
 // PageWithoutContent is the Page without any of the content methods.
 type PageWithoutContent interface {
 	RawContentProvider
+	RenderShortcodesProvider
 	resource.Resource
 	PageMetaProvider
 	resource.LanguageProvider
@@ -362,6 +363,11 @@ type RawContentProvider interface {
 	RawContent() string
 }
 
+type RenderShortcodesProvider interface {
+	// RenderShortcodes returns RawContent with any shortcodes rendered.
+	RenderShortcodes(context.Context) (template.HTML, error)
+}
+
 // RefProvider provides the methods needed to create reflinks to pages.
 type RefProvider interface {
 	// Ref returns an absolute URl to a page.

resources/page/page_nop.go

@@ -401,6 +401,10 @@ func (p *nopPage) RawContent() string {
 	return ""
 }
 
+func (p *nopPage) RenderShortcodes(ctx context.Context) (template.HTML, error) {
+	return "", nil
+}
+
 func (p *nopPage) ReadingTime(context.Context) int {
 	return 0
 }