Add --printUnusedTemplates

Fixes #9502

tpl/tplimpl/template.go

@@ -67,10 +67,11 @@ var embeddedTemplatesAliases = map[string][]string{
 }
 
 var (
-	_ tpl.TemplateManager    = (*templateExec)(nil)
-	_ tpl.TemplateHandler    = (*templateExec)(nil)
-	_ tpl.TemplateFuncGetter = (*templateExec)(nil)
-	_ tpl.TemplateFinder     = (*templateExec)(nil)
+	_ tpl.TemplateManager         = (*templateExec)(nil)
+	_ tpl.TemplateHandler         = (*templateExec)(nil)
+	_ tpl.TemplateFuncGetter      = (*templateExec)(nil)
+	_ tpl.TemplateFinder          = (*templateExec)(nil)
+	_ tpl.UnusedTemplatesProvider = (*templateExec)(nil)
 
 	_ tpl.Template = (*templateState)(nil)
 	_ tpl.Info     = (*templateState)(nil)
@@ -130,6 +131,11 @@ func newTemplateExec(d *deps.Deps) (*templateExec, error) {
 		funcMap[k] = v.Interface()
 	}
 
+	var templateUsageTracker map[string]templateInfo
+	if d.Cfg.GetBool("printUnusedTemplates") {
+		templateUsageTracker = make(map[string]templateInfo)
+	}
+
 	h := &templateHandler{
 		nameBaseTemplateName: make(map[string]string),
 		transformNotFound:    make(map[string]*templateState),
@@ -146,6 +152,8 @@ func newTemplateExec(d *deps.Deps) (*templateExec, error) {
 		layoutHandler:       output.NewLayoutHandler(),
 		layoutsFs:           d.BaseFs.Layouts.Fs,
 		layoutTemplateCache: make(map[layoutCacheKey]tpl.Template),
+
+		templateUsageTracker: templateUsageTracker,
 	}
 
 	if err := h.loadEmbedded(); err != nil {
@@ -225,13 +233,72 @@ func (t *templateExec) Execute(templ tpl.Template, wr io.Writer, data interface{
 		defer t.Metrics.MeasureSince(templ.Name(), time.Now())
 	}
 
+	if t.templateUsageTracker != nil {
+		if ts, ok := templ.(*templateState); ok {
+			t.templateUsageTrackerMu.Lock()
+			if _, found := t.templateUsageTracker[ts.Name()]; !found {
+				t.templateUsageTracker[ts.Name()] = ts.info
+			}
+
+			if !ts.baseInfo.IsZero() {
+				if _, found := t.templateUsageTracker[ts.baseInfo.name]; !found {
+					t.templateUsageTracker[ts.baseInfo.name] = ts.baseInfo
+				}
+			}
+			t.templateUsageTrackerMu.Unlock()
+		}
+	}
+
 	execErr := t.executor.Execute(templ, wr, data)
 	if execErr != nil {
 		execErr = t.addFileContext(templ, execErr)
 	}
+
 	return execErr
 }
 
+// TODO1
+func (t *templateExec) UnusedTemplates() []tpl.FileInfo {
+	if t.templateUsageTracker == nil {
+		return nil
+	}
+	var unused []tpl.FileInfo
+
+	for _, ti := range t.needsBaseof {
+		if _, found := t.templateUsageTracker[ti.name]; !found {
+			unused = append(unused, ti)
+		}
+	}
+
+	for _, ti := range t.baseof {
+		if _, found := t.templateUsageTracker[ti.name]; !found {
+			unused = append(unused, ti)
+		}
+	}
+
+	for _, ts := range t.main.templates {
+		ti := ts.info
+		if strings.HasPrefix(ti.name, "_internal/") {
+			continue
+		}
+		if strings.HasPrefix(ti.name, "partials/inline/pagination") {
+			// TODO(bep) we need to fix this. These are internal partials, but
+			// they may also be defined in the project, which currently could
+			// lead to some false negatives.
+			continue
+		}
+		if _, found := t.templateUsageTracker[ti.name]; !found {
+			unused = append(unused, ti)
+		}
+	}
+
+	sort.Slice(unused, func(i, j int) bool {
+		return unused[i].Name() < unused[j].Name()
+	})
+
+	return unused
+}
+
 func (t *templateExec) GetFunc(name string) (reflect.Value, bool) {
 	v, found := t.funcs[name]
 	return v, found
@@ -285,6 +352,10 @@ type templateHandler struct {
 	// Note that for shortcodes that same information is embedded in the
 	// shortcodeTemplates type.
 	templateInfo map[string]tpl.Info
+
+	// May be nil.
+	templateUsageTracker   map[string]templateInfo
+	templateUsageTrackerMu sync.Mutex
 }
 
 // AddTemplate parses and adds a template to the collection.