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

1 files changed, 18 insertions, 9 deletions

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")