tpl: Rework to handle both text and HTML templates

Before this commit, Hugo used `html/template` for all Go templates.

While this is a fine choice for HTML and maybe also RSS feeds, it is painful for plain text formats such as CSV, JSON etc.

This commit fixes that by using the `IsPlainText` attribute on the output format to decide what to use.

A couple of notes:

* The above requires a nonambiguous template name to type mapping. I.e. `/layouts/_default/list.json` will only work if there is only one JSON output format, `/layouts/_default/list.mytype.json` will always work.
* Ambiguous types will fall back to HTML.
* Partials inherits the text vs HTML identificator of the container template. This also means that plain text templates can only include plain text partials.
* Shortcode templates are, by definition, currently HTML templates only.

Fixes #3221

31 files changed, 1145 insertions, 777 deletions

diff --git a/deps/deps.go b/deps/deps.go
index 659f259dd..188863876 100644
--- a/deps/deps.go
+++ b/deps/deps.go
@@ -20,7 +20,7 @@ type Deps struct {
 	Log *jww.Notepad `json:"-"`
 
 	// The templates to use.
-	Tmpl tpl.Template `json:"-"`
+	Tmpl tpl.TemplateHandler `json:"-"`
 
 	// The file systems to use.
 	Fs *hugofs.Fs `json:"-"`
@@ -40,7 +40,7 @@ type Deps struct {
 	Language *helpers.Language
 
 	templateProvider ResourceProvider
-	WithTemplate     func(templ tpl.Template) error `json:"-"`
+	WithTemplate     func(templ tpl.TemplateHandler) error `json:"-"`
 
 	translationProvider ResourceProvider
 }
@@ -158,7 +158,7 @@ type DepsCfg struct {
 
 	// Template handling.
 	TemplateProvider ResourceProvider
-	WithTemplate     func(templ tpl.Template) error
+	WithTemplate     func(templ tpl.TemplateHandler) error
 
 	// i18n handling.
 	TranslationProvider ResourceProvider
diff --git a/hugolib/alias.go b/hugolib/alias.go
index d5eb35777..454744d9b 100644
--- a/hugolib/alias.go
+++ b/hugolib/alias.go
@@ -22,6 +22,8 @@ import (
 	"runtime"
 	"strings"
 
+	"github.com/spf13/hugo/tpl"
+
 	jww "github.com/spf13/jwalterweatherman"
 
 	"github.com/spf13/hugo/helpers"
@@ -35,18 +37,19 @@ const (
 var defaultAliasTemplates *template.Template
 
 func init() {
+	//TODO(bep) consolidate
 	defaultAliasTemplates = template.New("")
 	template.Must(defaultAliasTemplates.New("alias").Parse(alias))
 	template.Must(defaultAliasTemplates.New("alias-xhtml").Parse(aliasXHtml))
 }
 
 type aliasHandler struct {
-	Templates *template.Template
+	t         tpl.TemplateHandler
 	log       *jww.Notepad
 	allowRoot bool
 }
 
-func newAliasHandler(t *template.Template, l *jww.Notepad, allowRoot bool) aliasHandler {
+func newAliasHandler(t tpl.TemplateHandler, l *jww.Notepad, allowRoot bool) aliasHandler {
 	return aliasHandler{t, l, allowRoot}
 }
 
@@ -56,12 +59,19 @@ func (a aliasHandler) renderAlias(isXHTML bool, permalink string, page *Page) (i
 		t = "alias-xhtml"
 	}
 
-	template := defaultAliasTemplates
-	if a.Templates != nil {
-		template = a.Templates
-		t = "alias.html"
+	var templ *tpl.TemplateAdapter
+
+	if a.t != nil {
+		templ = a.t.Lookup("alias.html")
 	}
 
+	if templ == nil {
+		def := defaultAliasTemplates.Lookup(t)
+		if def != nil {
+			templ = &tpl.TemplateAdapter{def}
+		}
+
+	}
 	data := struct {
 		Permalink string
 		Page      *Page
@@ -71,7 +81,7 @@ func (a aliasHandler) renderAlias(isXHTML bool, permalink string, page *Page) (i
 	}
 
 	buffer := new(bytes.Buffer)
-	err := template.ExecuteTemplate(buffer, t, data)
+	err := templ.Execute(buffer, data)
 	if err != nil {
 		return nil, err
 	}
@@ -83,8 +93,7 @@ func (s *Site) writeDestAlias(path, permalink string, p *Page) (err error) {
 }
 
 func (s *Site) publishDestAlias(allowRoot bool, path, permalink string, p *Page) (err error) {
-
-	handler := newAliasHandler(s.Tmpl.Lookup("alias.html"), s.Log, allowRoot)
+	handler := newAliasHandler(s.Tmpl, s.Log, allowRoot)
 
 	isXHTML := strings.HasSuffix(path, ".xhtml")
 
diff --git a/hugolib/embedded_shortcodes_test.go b/hugolib/embedded_shortcodes_test.go
index 92821d0ef..45de0bf09 100644
--- a/hugolib/embedded_shortcodes_test.go
+++ b/hugolib/embedded_shortcodes_test.go
@@ -335,8 +335,8 @@ func TestShortcodeTweet(t *testing.T) {
 			th      = testHelper{cfg, fs, t}
 		)
 
-		withTemplate := func(templ tpl.Template) error {
-			templ.Funcs(tweetFuncMap)
+		withTemplate := func(templ tpl.TemplateHandler) error {
+			templ.(tpl.TemplateTestMocker).SetFuncs(tweetFuncMap)
 			return nil
 		}
 
@@ -390,8 +390,8 @@ func TestShortcodeInstagram(t *testing.T) {
 			th      = testHelper{cfg, fs, t}
 		)
 
-		withTemplate := func(templ tpl.Template) error {
-			templ.Funcs(instagramFuncMap)
+		withTemplate := func(templ tpl.TemplateHandler) error {
+			templ.(tpl.TemplateTestMocker).SetFuncs(instagramFuncMap)
 			return nil
 		}
 
diff --git a/hugolib/hugo_sites.go b/hugolib/hugo_sites.go
index 6c737f65a..1f090cf5e 100644
--- a/hugolib/hugo_sites.go
+++ b/hugolib/hugo_sites.go
@@ -127,11 +127,11 @@ func NewHugoSites(cfg deps.DepsCfg) (*HugoSites, error) {
 	return newHugoSites(cfg, sites...)
 }
 
-func (s *Site) withSiteTemplates(withTemplates ...func(templ tpl.Template) error) func(templ tpl.Template) error {
-	return func(templ tpl.Template) error {
-		templ.LoadTemplates(s.PathSpec.GetLayoutDirPath())
+func (s *Site) withSiteTemplates(withTemplates ...func(templ tpl.TemplateHandler) error) func(templ tpl.TemplateHandler) error {
+	return func(templ tpl.TemplateHandler) error {
+		templ.LoadTemplates(s.PathSpec.GetLayoutDirPath(), "")
 		if s.PathSpec.ThemeSet() {
-			templ.LoadTemplatesWithPrefix(s.PathSpec.GetThemeDir()+"/layouts", "theme")
+			templ.LoadTemplates(s.PathSpec.GetThemeDir()+"/layouts", "theme")
 		}
 
 		for _, wt := range withTemplates {
diff --git a/hugolib/page.go b/hugolib/page.go
index fa9f40922..5a04c6ce7 100644
--- a/hugolib/page.go
+++ b/hugolib/page.go
@@ -1384,13 +1384,14 @@ func (p *Page) prepareLayouts() error {
 	if p.Kind == KindPage {
 		if !p.IsRenderable() {
 			self := "__" + p.UniqueID()
-			_, err := p.s.Tmpl.GetClone().New(self).Parse(string(p.Content))
+			err := p.s.Tmpl.AddLateTemplate(self, string(p.Content))
 			if err != nil {
 				return err
 			}
 			p.selfLayout = self
 		}
 	}
+
 	return nil
 }
 
diff --git a/hugolib/page_output.go b/hugolib/page_output.go
index f47343cb5..58d09d688 100644
--- a/hugolib/page_output.go
+++ b/hugolib/page_output.go
@@ -110,9 +110,29 @@ func (p *PageOutput) Render(layout ...string) template.HTML {
 	l, err := p.layouts(layout...)
 	if err != nil {
 		helpers.DistinctErrorLog.Printf("in .Render: Failed to resolve layout %q for page %q", layout, p.pathOrTitle())
-		return template.HTML("")
+		return ""
 	}
-	return p.s.Tmpl.ExecuteTemplateToHTML(p, l...)
+
+	for _, layout := range l {
+		templ := p.s.Tmpl.Lookup(layout)
+		if templ == nil {
+			// This is legacy from when we had only one output format and
+			// HTML templates only. Some have references to layouts without suffix.
+			// We default to good old HTML.
+			templ = p.s.Tmpl.Lookup(layout + ".html")
+		}
+		if templ != nil {
+			res, err := templ.ExecuteToString(p)
+			if err != nil {
+				helpers.DistinctErrorLog.Printf("in .Render: Failed to execute template %q for page %q", layout, p.pathOrTitle())
+				return template.HTML("")
+			}
+			return template.HTML(res)
+		}
+	}
+
+	return ""
+
 }
 
 func (p *Page) Render(layout ...string) template.HTML {
diff --git a/hugolib/shortcode.go b/hugolib/shortcode.go
index d165c778b..d72a96faa 100644
--- a/hugolib/shortcode.go
+++ b/hugolib/shortcode.go
@@ -177,7 +177,7 @@ var isInnerShortcodeCache = struct {
 // to avoid potential costly look-aheads for closing tags we look inside the template itself
 // we could change the syntax to self-closing tags, but that would make users cry
 // the value found is cached
-func isInnerShortcode(t *template.Template) (bool, error) {
+func isInnerShortcode(t tpl.TemplateExecutor) (bool, error) {
 	isInnerShortcodeCache.RLock()
 	m, ok := isInnerShortcodeCache.m[t.Name()]
 	isInnerShortcodeCache.RUnlock()
@@ -188,10 +188,7 @@ func isInnerShortcode(t *template.Template) (bool, error) {
 
 	isInnerShortcodeCache.Lock()
 	defer isInnerShortcodeCache.Unlock()
-	if t.Tree == nil {
-		return false, errors.New("Template failed to compile")
-	}
-	match, _ := regexp.MatchString("{{.*?\\.Inner.*?}}", t.Tree.Root.String())
+	match, _ := regexp.MatchString("{{.*?\\.Inner.*?}}", t.Tree())
 	isInnerShortcodeCache.m[t.Name()] = match
 
 	return match, nil
@@ -398,8 +395,6 @@ Loop:
 		case tScName:
 			sc.name = currItem.val
 			tmpl := getShortcodeTemplate(sc.name, p.s.Tmpl)
-			{
-			}
 			if tmpl == nil {
 				return sc, fmt.Errorf("Unable to locate template for shortcode %q in page %q", sc.name, p.Path())
 			}
@@ -570,7 +565,10 @@ func replaceShortcodeTokens(source []byte, prefix string, replacements map[strin
 	return source, nil
 }
 
-func getShortcodeTemplate(name string, t tpl.Template) *template.Template {
+func getShortcodeTemplate(name string, t tpl.TemplateHandler) *tpl.TemplateAdapter {
+	isInnerShortcodeCache.RLock()
+	defer isInnerShortcodeCache.RUnlock()
+
 	if x := t.Lookup("shortcodes/" + name + ".html"); x != nil {
 		return x
 	}
@@ -580,7 +578,7 @@ func getShortcodeTemplate(name string, t tpl.Template) *template.Template {
 	return t.Lookup("_internal/shortcodes/" + name + ".html")
 }
 
-func renderShortcodeWithPage(tmpl *template.Template, data *ShortcodeWithPage) string {
+func renderShortcodeWithPage(tmpl tpl.Template, data *ShortcodeWithPage) string {
 	buffer := bp.GetBuffer()
 	defer bp.PutBuffer(buffer)
 
diff --git a/hugolib/shortcode_test.go b/hugolib/shortcode_test.go
index 28b03aa9b..3d1922462 100644
--- a/hugolib/shortcode_test.go
+++ b/hugolib/shortcode_test.go
@@ -30,7 +30,7 @@ import (
 )
 
 // TODO(bep) remove
-func pageFromString(in, filename string, withTemplate ...func(templ tpl.Template) error) (*Page, error) {
+func pageFromString(in, filename string, withTemplate ...func(templ tpl.TemplateHandler) error) (*Page, error) {
 	s := newTestSite(nil)
 	if len(withTemplate) > 0 {
 		// Have to create a new site
@@ -47,11 +47,11 @@ func pageFromString(in, filename string, withTemplate ...func(templ tpl.Template
 	return s.NewPageFrom(strings.NewReader(in), filename)
 }
 
-func CheckShortCodeMatch(t *testing.T, input, expected string, withTemplate func(templ tpl.Template) error) {
+func CheckShortCodeMatch(t *testing.T, input, expected string, withTemplate func(templ tpl.TemplateHandler) error) {
 	CheckShortCodeMatchAndError(t, input, expected, withTemplate, false)
 }
 
-func CheckShortCodeMatchAndError(t *testing.T, input, expected string, withTemplate func(templ tpl.Template) error, expectError bool) {
+func CheckShortCodeMatchAndError(t *testing.T, input, expected string, withTemplate func(templ tpl.TemplateHandler) error, expectError bool) {
 
 	cfg, fs := newTestCfg()
 
@@ -100,8 +100,9 @@ func TestNonSC(t *testing.T) {
 // Issue #929
 func TestHyphenatedSC(t *testing.T) {
 	t.Parallel()
-	wt := func(tem tpl.Template) error {
-		tem.AddInternalShortcode("hyphenated-video.html", `Playing Video {{ .Get 0 }}`)
+	wt := func(tem tpl.TemplateHandler) error {
+
+		tem.AddTemplate("_internal/shortcodes/hyphenated-video.html", `Playing Video {{ .Get 0 }}`)
 		return nil
 	}
 
@@ -111,8 +112,8 @@ func TestHyphenatedSC(t *testing.T) {
 // Issue #1753
 func TestNoTrailingNewline(t *testing.T) {
 	t.Parallel()
-	wt := func(tem tpl.Template) error {
-		tem.AddInternalShortcode("a.html", `{{ .Get 0 }}`)
+	wt := func(tem tpl.TemplateHandler) error {
+		tem.AddTemplate("_internal/shortcodes/a.html", `{{ .Get 0 }}`)
 		return nil
 	}
 
@@ -121,8 +122,8 @@ func TestNoTrailingNewline(t *testing.T) {
 
 func TestPositionalParamSC(t *testing.T) {
 	t.Parallel()
-	wt := func(tem tpl.Template) error {
-		tem.AddInternalShortcode("video.html", `Playing Video {{ .Get 0 }}`)
+	wt := func(tem tpl.TemplateHandler) error {
+		tem.AddTemplate("_internal/shortcodes/video.html", `Playing Video {{ .Get 0 }}`)
 		return nil
 	}
 
@@ -135,8 +136,8 @@ func TestPositionalParamSC(t *testing.T) {
 
 func TestPositionalParamIndexOutOfBounds(t *testing.T) {
 	t.Parallel()
-	wt := func(tem tpl.Template) error {
-		tem.AddInternalShortcode("video.html", `Playing Video {{ .Get 1 }}`)
+	wt := func(tem tpl.TemplateHandler) error {
+		tem.AddTemplate("_internal/shortcodes/video.html", `Playing Video {{ .Get 1 }}`)
 		return nil
 	}
 	CheckShortCodeMatch(t, "{{< video 47238zzb >}}", "Playing Video error: index out of range for positional param at position 1", wt)
@@ -146,8 +147,8 @@ func TestPositionalParamIndexOutOfBounds(t *testing.T) {
 
 func TestNamedParamSC(t *testing.T) {
 	t.Parallel()
-	wt := func(tem tpl.Template) error {
-		tem.AddInternalShortcode("img.html", `<img{{ with .Get "src" }} src="{{.}}"{{end}}{{with .Get "class"}} class="{{.}}"{{end}}>`)
+	wt := func(tem tpl.TemplateHandler) error {
+		tem.AddTemplate("_internal/shortcodes/img.html", `<img{{ with .Get "src" }} src="{{.}}"{{end}}{{with .Get "class"}} class="{{.}}"{{end}}>`)
 		return nil
 	}
 	CheckShortCodeMatch(t, `{{< img src="one" >}}`, `<img src="one">`, wt)
@@ -161,10 +162,10 @@ func TestNamedParamSC(t *testing.T) {
 // Issue #2294
 func TestNestedNamedMissingParam(t *testing.T) {
 	t.Parallel()
-	wt := func(tem tpl.Template) error {
-		tem.AddInternalShortcode("acc.html", `<div class="acc">{{ .Inner }}</div>`)
-		tem.AddInternalShortcode("div.html", `<div {{with .Get "class"}} class="{{ . }}"{{ end }}>{{ .Inner }}</div>`)
-		tem.AddInternalShortcode("div2.html", `<div {{with .Get 0}} class="{{ . }}"{{ end }}>{{ .Inner }}</div>`)
+	wt := func(tem tpl.TemplateHandler) error {
+		tem.AddTemplate("_internal/shortcodes/acc.html", `<div class="acc">{{ .Inner }}</div>`)
+		tem.AddTemplate("_internal/shortcodes/div.html", `<div {{with .Get "class"}} class="{{ . }}"{{ end }}>{{ .Inner }}</div>`)
+		tem.AddTemplate("_internal/shortcodes/div2.html", `<div {{with .Get 0}} class="{{ . }}"{{ end }}>{{ .Inner }}</div>`)
 		return nil
 	}
 	CheckShortCodeMatch(t,
@@ -174,10 +175,10 @@ func TestNestedNamedMissingParam(t *testing.T) {
 
 func TestIsNamedParamsSC(t *testing.T) {
 	t.Parallel()
-	wt := func(tem tpl.Template) error {
-		tem.AddInternalShortcode("byposition.html", `<div id="{{ .Get 0 }}">`)
-		tem.AddInternalShortcode("byname.html", `<div id="{{ .Get "id" }}">`)
-		tem.AddInternalShortcode("ifnamedparams.html", `<div id="{{ if .IsNamedParams }}{{ .Get "id" }}{{ else }}{{ .Get 0 }}{{end}}">`)
+	wt := func(tem tpl.TemplateHandler) error {
+		tem.AddTemplate("_internal/shortcodes/byposition.html", `<div id="{{ .Get 0 }}">`)
+		tem.AddTemplate("_internal/shortcodes/byname.html", `<div id="{{ .Get "id" }}">`)
+		tem.AddTemplate("_internal/shortcodes/ifnamedparams.html", `<div id="{{ if .IsNamedParams }}{{ .Get "id" }}{{ else }}{{ .Get 0 }}{{end}}">`)
 		return nil
 	}
 	CheckShortCodeMatch(t, `{{< ifnamedparams id="name" >}}`, `<div id="name">`, wt)
@@ -190,8 +191,8 @@ func TestIsNamedParamsSC(t *testing.T) {
 
 func TestInnerSC(t *testing.T) {
 	t.Parallel()
-	wt := func(tem tpl.Template) error {
-		tem.AddInternalShortcode("inside.html", `<div{{with .Get "class"}} class="{{.}}"{{end}}>{{ .Inner }}</div>`)
+	wt := func(tem tpl.TemplateHandler) error {
+		tem.AddTemplate("_internal/shortcodes/inside.html", `<div{{with .Get "class"}} class="{{.}}"{{end}}>{{ .Inner }}</div>`)
 		return nil
 	}
 	CheckShortCodeMatch(t, `{{< inside class="aspen" >}}`, `<div class="aspen"></div>`, wt)
@@ -201,8 +202,8 @@ func TestInnerSC(t *testing.T) {
 
 func TestInnerSCWithMarkdown(t *testing.T) {
 	t.Parallel()
-	wt := func(tem tpl.Template) error {
-		tem.AddInternalShortcode("inside.html", `<div{{with .Get "class"}} class="{{.}}"{{end}}>{{ .Inner }}</div>`)
+	wt := func(tem tpl.TemplateHandler) error {
+		tem.AddTemplate("_internal/shortcodes/inside.html", `<div{{with .Get "class"}} class="{{.}}"{{end}}>{{ .Inner }}</div>`)
 		return nil
 	}
 	CheckShortCodeMatch(t, `{{% inside %}}
@@ -215,8 +216,8 @@ func TestInnerSCWithMarkdown(t *testing.T) {
 
 func TestInnerSCWithAndWithoutMarkdown(t *testing.T) {
 	t.Parallel()
-	wt := func(tem tpl.Template) error {
-		tem.AddInternalShortcode("inside.html", `<div{{with .Get "class"}} class="{{.}}"{{end}}>{{ .Inner }}</div>`)
+	wt := func(tem tpl.TemplateHandler) error {
+		tem.AddTemplate("_internal/shortcodes/inside.html", `<div{{with .Get "class"}} class="{{.}}"{{end}}>{{ .Inner }}</div>`)
 		return nil
 	}
 	CheckShortCodeMatch(t, `{{% inside %}}
@@ -246,9 +247,9 @@ func TestEmbeddedSC(t *testing.T) {
 
 func TestNestedSC(t *testing.T) {
 	t.Parallel()
-	wt := func(tem tpl.Template) error {
-		tem.AddInternalShortcode("scn1.html", `<div>Outer, inner is {{ .Inner }}</div>`)
-		tem.AddInternalShortcode("scn2.html", `<div>SC2</div>`)
+	wt := func(tem tpl.TemplateHandler) error {
+		tem.AddTemplate("_internal/shortcodes/scn1.html", `<div>Outer, inner is {{ .Inner }}</div>`)
+		tem.AddTemplate("_internal/shortcodes/scn2.html", `<div>SC2</div>`)
 		return nil
 	}
 	CheckShortCodeMatch(t, `{{% scn1 %}}{{% scn2 %}}{{% /scn1 %}}`, "<div>Outer, inner is <div>SC2</div>\n</div>", wt)
@@ -258,10 +259,10 @@ func TestNestedSC(t *testing.T) {
 
 func TestNestedComplexSC(t *testing.T) {
 	t.Parallel()
-	wt := func(tem tpl.Template) error {
-		tem.AddInternalShortcode("row.html", `-row-{{ .Inner}}-rowStop-`)
-		tem.AddInternalShortcode("column.html", `-col-{{.Inner    }}-colStop-`)
-		tem.AddInternalShortcode("aside.html", `-aside-{{    .Inner  }}-asideStop-`)
+	wt := func(tem tpl.TemplateHandler) error {
+		tem.AddTemplate("_internal/shortcodes/row.html", `-row-{{ .Inner}}-rowStop-`)
+		tem.AddTemplate("_internal/shortcodes/column.html", `-col-{{.Inner    }}-colStop-`)
+		tem.AddTemplate("_internal/shortcodes/aside.html", `-aside-{{    .Inner  }}-asideStop-`)
 		return nil
 	}
 	CheckShortCodeMatch(t, `{{< row >}}1-s{{% column %}}2-**s**{{< aside >}}3-**s**{{< /aside >}}4-s{{% /column %}}5-s{{< /row >}}6-s`,
@@ -274,10 +275,10 @@ func TestNestedComplexSC(t *testing.T) {
 
 func TestParentShortcode(t *testing.T) {
 	t.Parallel()
-	wt := func(tem tpl.Template) error {
-		tem.AddInternalShortcode("r1.html", `1: {{ .Get "pr1" }} {{ .Inner }}`)
-		tem.AddInternalShortcode("r2.html", `2: {{ .Parent.Get "pr1" }}{{ .Get "pr2" }} {{ .Inner }}`)
-		tem.AddInternalShortcode("r3.html", `3: {{ .Parent.Parent.Get "pr1" }}{{ .Parent.Get "pr2" }}{{ .Get "pr3" }} {{ .Inner }}`)
+	wt := func(tem tpl.TemplateHandler) error {
+		tem.AddTemplate("_internal/shortcodes/r1.html", `1: {{ .Get "pr1" }} {{ .Inner }}`)
+		tem.AddTemplate("_internal/shortcodes/r2.html", `2: {{ .Parent.Get "pr1" }}{{ .Get "pr2" }} {{ .Inner }}`)
+		tem.AddTemplate("_internal/shortcodes/r3.html", `3: {{ .Parent.Parent.Get "pr1" }}{{ .Parent.Get "pr2" }}{{ .Get "pr3" }} {{ .Inner }}`)
 		return nil
 	}
 	CheckShortCodeMatch(t, `{{< r1 pr1="p1" >}}1: {{< r2 pr2="p2" >}}2: {{< r3 pr3="p3" >}}{{< /r3 >}}{{< /r2 >}}{{< /r1 >}}`,
@@ -342,13 +343,13 @@ func TestExtractShortcodes(t *testing.T) {
 			fmt.Sprintf("Hello %sworld%s. And that's it.", testScPlaceholderRegexp, testScPlaceholderRegexp), ""},
 	} {
 
-		p, _ := pageFromString(simplePage, "simple.md", func(templ tpl.Template) error {
-			templ.AddInternalShortcode("tag.html", `tag`)
-			templ.AddInternalShortcode("sc1.html", `sc1`)
-			templ.AddInternalShortcode("sc2.html", `sc2`)
-			templ.AddInternalShortcode("inner.html", `{{with .Inner }}{{ . }}{{ end }}`)
-			templ.AddInternalShortcode("inner2.html", `{{.Inner}}`)
-			templ.AddInternalShortcode("inner3.html", `{{.Inner}}`)
+		p, _ := pageFromString(simplePage, "simple.md", func(templ tpl.TemplateHandler) error {
+			templ.AddTemplate("_internal/shortcodes/tag.html", `tag`)
+			templ.AddTemplate("_internal/shortcodes/sc1.html", `sc1`)
+			templ.AddTemplate("_internal/shortcodes/sc2.html", `sc2`)
+			templ.AddTemplate("_internal/shortcodes/inner.html", `{{with .Inner }}{{ . }}{{ end }}`)
+			templ.AddTemplate("_internal/shortcodes/inner2.html", `{{.Inner}}`)
+			templ.AddTemplate("_internal/shortcodes/inner3.html", `{{.Inner}}`)
 			return nil
 		})
 
@@ -517,14 +518,14 @@ tags:
 		sources[i] = source.ByteSource{Name: filepath.FromSlash(test.contentPath), Content: []byte(test.content)}
 	}
 
-	addTemplates := func(templ tpl.Template) error {
+	addTemplates := func(templ tpl.TemplateHandler) error {
 		templ.AddTemplate("_default/single.html", "{{.Content}}")
 
-		templ.AddInternalShortcode("b.html", `b`)
-		templ.AddInternalShortcode("c.html", `c`)
-		templ.AddInternalShortcode("d.html", `d`)
-		templ.AddInternalShortcode("menu.html", `{{ len (index .Page.Menus "main").Children }}`)
-		templ.AddInternalShortcode("tags.html", `{{ len .Page.Site.Taxonomies.tags }}`)
+		templ.AddTemplate("_internal/shortcodes/b.html", `b`)
+		templ.AddTemplate("_internal/shortcodes/c.html", `c`)
+		templ.AddTemplate("_internal/shortcodes/d.html", `d`)
+		templ.AddTemplate("_internal/shortcodes/menu.html", `{{ len (index .Page.Menus "main").Children }}`)
+		templ.AddTemplate("_internal/shortcodes/tags.html", `{{ len .Page.Site.Taxonomies.tags }}`)
 
 		return nil
 
diff --git a/hugolib/site.go b/hugolib/site.go
index f8a57dfa2..1808a090e 100644
--- a/hugolib/site.go
+++ b/hugolib/site.go
@@ -193,7 +193,7 @@ func NewSite(cfg deps.DepsCfg) (*Site, error) {
 // NewSiteDefaultLang creates a new site in the default language.
 // The site will have a template system loaded and ready to use.
 // Note: This is mainly used in single site tests.
-func NewSiteDefaultLang(withTemplate ...func(templ tpl.Template) error) (*Site, error) {
+func NewSiteDefaultLang(withTemplate ...func(templ tpl.TemplateHandler) error) (*Site, error) {
 	v := viper.New()
 	loadDefaultSettingsFor(v)
 	return newSiteForLang(helpers.NewDefaultLanguage(v), withTemplate...)
@@ -202,15 +202,15 @@ func NewSiteDefaultLang(withTemplate ...func(templ tpl.Template) error) (*Site,
 // NewEnglishSite creates a new site in English language.
 // The site will have a template system loaded and ready to use.
 // Note: This is mainly used in single site tests.
-func NewEnglishSite(withTemplate ...func(templ tpl.Template) error) (*Site, error) {
+func NewEnglishSite(withTemplate ...func(templ tpl.TemplateHandler) error) (*Site, error) {
 	v := viper.New()
 	loadDefaultSettingsFor(v)
 	return newSiteForLang(helpers.NewLanguage("en", v), withTemplate...)
 }
 
 // newSiteForLang creates a new site in the given language.
-func newSiteForLang(lang *helpers.Language, withTemplate ...func(templ tpl.Template) error) (*Site, error) {
-	withTemplates := func(templ tpl.Template) error {
+func newSiteForLang(lang *helpers.Language, withTemplate ...func(templ tpl.TemplateHandler) error) (*Site, error) {
+	withTemplates := func(templ tpl.TemplateHandler) error {
 		for _, wt := range withTemplate {
 			if err := wt(templ); err != nil {
 				return err
@@ -1911,14 +1911,14 @@ Your rendered home page is blank: /index.html is zero-length
 }
 
 func (s *Site) renderForLayouts(name string, d interface{}, w io.Writer, layouts ...string) error {
-	layout, found := s.findFirstLayout(layouts...)
-	if !found {
+	templ := s.findFirstTemplate(layouts...)
+	if templ == nil {
 		s.Log.WARN.Printf("[%s] Unable to locate layout for %s: %s\n", s.Language.Lang, name, layouts)
 
 		return nil
 	}</