Rework template handling for function and map lookups

This is a big commit, but it deletes lots of code and simplifies a lot.

* Resolving the template funcs at execution time means we don't have to create template clones per site
* Having a custom map resolver means that we can remove the AST lower case transformation for the special lower case Params map

Not only is the above easier to reason about, it's also faster, especially if you have more than one language, as in the benchmark below:

```
name                          old time/op    new time/op    delta
SiteNew/Deep_content_tree-16    53.7ms ± 0%    48.1ms ± 2%  -10.38%  (p=0.029 n=4+4)

name                          old alloc/op   new alloc/op   delta
SiteNew/Deep_content_tree-16    41.0MB ± 0%    36.8MB ± 0%  -10.26%  (p=0.029 n=4+4)

name                          old allocs/op  new allocs/op  delta
SiteNew/Deep_content_tree-16      481k ± 0%      410k ± 0%  -14.66%  (p=0.029 n=4+4)
```

This should be even better if you also have lots of templates.

Closes #6594

1 files changed, 5 insertions, 5 deletions

diff --git a/hugolib/site.go b/hugolib/site.go
index 1df7d6076..67ddff4d9 100644
--- a/hugolib/site.go
+++ b/hugolib/site.go
@@ -474,7 +474,7 @@ func NewSite(cfg deps.DepsCfg) (*Site, error) {
 // The site will have a template system loaded and ready to use.
 // Note: This is mainly used in single site tests.
 // TODO(bep) test refactor -- remove
-func NewSiteDefaultLang(withTemplate ...func(templ tpl.TemplateHandler) error) (*Site, error) {
+func NewSiteDefaultLang(withTemplate ...func(templ tpl.TemplateManager) error) (*Site, error) {
 	v := viper.New()
 	if err := loadDefaultSettingsFor(v); err != nil {
 		return nil, err
@@ -486,7 +486,7 @@ func NewSiteDefaultLang(withTemplate ...func(templ tpl.TemplateHandler) error) (
 // The site will have a template system loaded and ready to use.
 // Note: This is mainly used in single site tests.
 // TODO(bep) test refactor -- remove
-func NewEnglishSite(withTemplate ...func(templ tpl.TemplateHandler) error) (*Site, error) {
+func NewEnglishSite(withTemplate ...func(templ tpl.TemplateManager) error) (*Site, error) {
 	v := viper.New()
 	if err := loadDefaultSettingsFor(v); err != nil {
 		return nil, err
@@ -495,8 +495,8 @@ func NewEnglishSite(withTemplate ...func(templ tpl.TemplateHandler) error) (*Sit
 }
 
 // newSiteForLang creates a new site in the given language.
-func newSiteForLang(lang *langs.Language, withTemplate ...func(templ tpl.TemplateHandler) error) (*Site, error) {
-	withTemplates := func(templ tpl.TemplateHandler) error {
+func newSiteForLang(lang *langs.Language, withTemplate ...func(templ tpl.TemplateManager) error) (*Site, error) {
+	withTemplates := func(templ tpl.TemplateManager) error {
 		for _, wt := range withTemplate {
 			if err := wt(templ); err != nil {
 				return err
@@ -1589,7 +1589,7 @@ func (s *Site) renderForLayouts(name, outputFormat string, d interface{}, w io.W
 		return nil
 	}
 
-	if err = templ.Execute(w, d); err != nil {
+	if err = s.Tmpl.Execute(templ, w, d); err != nil {
 		return _errors.Wrapf(err, "render of %q failed", name)
 	}
 	return