Reimplement and simplify Hugo's template system

See #13541 for details.

Fixes #13545
Fixes #13515
Closes #7964
Closes #13365
Closes #12988
Closes #4891

hugolib/hugo_sites_build.go

@@ -494,17 +494,17 @@ func (s *Site) executeDeferredTemplates(de *deps.DeferredExecutions) error {
 				defer deferred.Mu.Unlock()
 
 				if !deferred.Executed {
-					tmpl := s.Deps.Tmpl()
-					templ, found := tmpl.Lookup(deferred.TemplateName)
-					if !found {
-						panic(fmt.Sprintf("template %q not found", deferred.TemplateName))
+					tmpl := s.Deps.GetTemplateStore()
+					ti := s.TemplateStore.LookupByPath(deferred.TemplatePath)
+					if ti == nil {
+						panic(fmt.Sprintf("template %q not found", deferred.TemplatePath))
 					}
 
 					if err := func() error {
 						buf := bufferpool.GetBuffer()
 						defer bufferpool.PutBuffer(buf)
 
-						err = tmpl.ExecuteWithContext(deferred.Ctx, templ, buf, deferred.Data)
+						err = tmpl.ExecuteWithContext(deferred.Ctx, ti, buf, deferred.Data)
 						if err != nil {
 							return err
 						}
@@ -577,9 +577,13 @@ func (h *HugoSites) printUnusedTemplatesOnce() error {
 	h.printUnusedTemplatesInit.Do(func() {
 		conf := h.Configs.Base
 		if conf.PrintUnusedTemplates {
-			unusedTemplates := h.Tmpl().(tpl.UnusedTemplatesProvider).UnusedTemplates()
+			unusedTemplates := h.GetTemplateStore().UnusedTemplates()
 			for _, unusedTemplate := range unusedTemplates {
-				h.Log.Warnf("Template %s is unused, source file %s", unusedTemplate.Name(), unusedTemplate.Filename())
+				if unusedTemplate.Fi != nil {
+					h.Log.Warnf("Template %s is unused, source %q", unusedTemplate.PathInfo.Path(), unusedTemplate.Fi.Meta().Filename)
+				} else {
+					h.Log.Warnf("Template %s is unused", unusedTemplate.PathInfo.Path())
+				}
 			}
 		}
 	})
@@ -954,7 +958,7 @@ func (h *HugoSites) processPartialFileEvents(ctx context.Context, l logg.LevelLo
 		case files.ComponentFolderLayouts:
 			tmplChanged = true
 			templatePath := pathInfo.Unnormalized().TrimLeadingSlash().PathNoLang()
-			if !h.Tmpl().HasTemplate(templatePath) {
+			if !h.GetTemplateStore().HasTemplate(templatePath) {
 				tmplAdded = true
 			}
 
@@ -974,8 +978,9 @@ func (h *HugoSites) processPartialFileEvents(ctx context.Context, l logg.LevelLo
 				}
 			} else {
 				logger.Println("Template changed", pathInfo.Path())
-				if templ, found := h.Tmpl().GetIdentity(templatePath); found {
-					changes = append(changes, templ)
+				id := h.GetTemplateStore().GetIdentity(pathInfo.Path())
+				if id != nil {
+					changes = append(changes, id)
 				} else {
 					changes = append(changes, pathInfo)
 				}
@@ -1084,7 +1089,6 @@ func (h *HugoSites) processPartialFileEvents(ctx context.Context, l logg.LevelLo
 
 	changed := &WhatChanged{
 		needsPagesAssembly: needsPagesAssemble,
-		identitySet:        make(identity.Identities),
 	}
 	changed.Add(changes...)
 
@@ -1106,17 +1110,39 @@ func (h *HugoSites) processPartialFileEvents(ctx context.Context, l logg.LevelLo
 		}
 	}
 
-	h.Deps.OnChangeListeners.Notify(changed.Changes()...)
+	changes2 := changed.Changes()
+	h.Deps.OnChangeListeners.Notify(changes2...)
 
 	if err := h.resolveAndClearStateForIdentities(ctx, l, cacheBusterOr, changed.Drain()); err != nil {
 		return err
 	}
 
-	if tmplChanged || i18nChanged {
+	if tmplChanged {
 		if err := loggers.TimeTrackfn(func() (logg.LevelLogger, error) {
-			// TODO(bep) this could probably be optimized to somehow
-			// only load the changed templates and its dependencies, but that is non-trivial.
+			depsFinder := identity.NewFinder(identity.FinderConfig{})
 			ll := l.WithField("substep", "rebuild templates")
+			s := h.Sites[0]
+			if err := s.Deps.TemplateStore.RefreshFiles(func(fi hugofs.FileMetaInfo) bool {
+				pi := fi.Meta().PathInfo
+				for _, id := range changes2 {
+					if depsFinder.Contains(pi, id, -1) > 0 {
+						return true
+					}
+				}
+				return false
+			}); err != nil {
+				return ll, err
+			}
+
+			return ll, nil
+		}); err != nil {
+			return err
+		}
+	}
+
+	if i18nChanged {
+		if err := loggers.TimeTrackfn(func() (logg.LevelLogger, error) {
+			ll := l.WithField("substep", "rebuild i18n")
 			var prototype *deps.Deps
 			for i, s := range h.Sites {
 				if err := s.Deps.Compile(prototype); err != nil {