Fix regression of renderer (#16091)

* Fix regression of renderer

* Fix render setting load twice bug

modules/markup/renderer.go

@@ -48,6 +48,7 @@ type RenderContext struct {
 type Renderer interface {
 	Name() string // markup format name
 	Extensions() []string
+	NeedPostProcess() bool
 	Render(ctx *RenderContext, input io.Reader, output io.Writer) error
 }
 
@@ -94,7 +95,7 @@ func RenderString(ctx *RenderContext, content string) (string, error) {
 	return buf.String(), nil
 }
 
-func render(ctx *RenderContext, parser Renderer, input io.Reader, output io.Writer) error {
+func render(ctx *RenderContext, renderer Renderer, input io.Reader, output io.Writer) error {
 	var wg sync.WaitGroup
 	var err error
 	pr, pw := io.Pipe()
@@ -103,6 +104,7 @@ func render(ctx *RenderContext, parser Renderer, input io.Reader, output io.Writ
 		_ = pw.Close()
 	}()
 
+	if renderer.NeedPostProcess() {
 		pr2, pw2 := io.Pipe()
 		defer func() {
 			_ = pr2.Close()
@@ -124,8 +126,16 @@ func render(ctx *RenderContext, parser Renderer, input io.Reader, output io.Writ
 			_ = pw2.Close()
 			wg.Done()
 		}()
-
-	if err1 := parser.Render(ctx, input, pw); err1 != nil {
+	} else {
+		wg.Add(1)
+		go func() {
+			buf := SanitizeReader(pr)
+			_, err = io.Copy(output, buf)
+			_ = pr.Close()
+			wg.Done()
+		}()
+	}
+	if err1 := renderer.Render(ctx, input, pw); err1 != nil {
 		return err1
 	}
 	_ = pw.Close()

modules/setting/markup.go

@@ -38,6 +38,8 @@ type MarkupSanitizerRule struct {
 }
 
 func newMarkup() {
+	ExternalMarkupRenderers = make([]MarkupRenderer, 0, 10)
+	ExternalSanitizerRules = make([]MarkupSanitizerRule, 0, 10)
 	for _, sec := range Cfg.Section("markup").ChildSections() {
 		name := strings.TrimPrefix(sec.Name(), "markup.")
 		if name == "" {