improve comment, fix external render ctx check

Author: wxiaoguang

Diff for: modules/markup/external/external.go

@@ -102,7 +102,7 @@ func (p *Renderer) Render(ctx *markup.RenderContext, input io.Reader, output io.
 
 		_, err = io.Copy(f, input)
 		if err != nil {
-			f.Close()
+			_ = f.Close()
 			return fmt.Errorf("%s write data to temp file when rendering %s failed: %w", p.Name(), p.Command, err)
 		}
 
@@ -113,10 +113,9 @@ func (p *Renderer) Render(ctx *markup.RenderContext, input io.Reader, output io.
 		args = append(args, f.Name())
 	}
 
-	if ctx == nil || ctx.Ctx == nil {
-		if ctx == nil {
-			log.Warn("RenderContext not provided defaulting to empty ctx")
-			ctx = &markup.RenderContext{}
+	if ctx.Ctx == nil {
+		if !setting.IsProd || setting.IsInTesting {
+			panic("RenderContext did not provide context")
 		}
 		log.Warn("RenderContext did not provide context, defaulting to Shutdown context")
 		ctx.Ctx = graceful.GetManager().ShutdownContext()

Diff for: modules/markup/render.go

@@ -171,7 +171,8 @@ func render(ctx *RenderContext, renderer Renderer, input io.Reader, output io.Wr
 	finalProcessor := ctx.RenderInternal.Init(output)
 	defer finalProcessor.Close()
 
-	// input -> pw1 -> pr1 -> renderer -> pw2 -> pr2 -> SanitizeReader -> finalProcessor -> output
+	// input -> (pw1=pr1) -> renderer -> (pw2=pr2) -> SanitizeReader -> finalProcessor -> output
+	// no sanitizer: input -> (pw1=pr1) -> renderer -> pw2(finalProcessor) -> output
 	pr1, pw1, close1 := pipes()
 	defer close1()