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, 4 insertions, 4 deletions

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
 		}