Fix data race in non-renderable pages

Fixes #1601

hugolib/page.go

@@ -66,6 +66,7 @@ type Page struct {
 	contentType         string
 	renderable          bool
 	Layout              string
+	layoutsCalculated   []string
 	linkTitle           string
 	frontmatter         []byte
 	rawContent          []byte
@@ -288,6 +289,10 @@ func (p *Page) Section() string {
 }
 
 func (p *Page) layouts(l ...string) []string {
+	if len(p.layoutsCalculated) > 0 {
+		return p.layoutsCalculated
+	}
+
 	if p.Layout != "" {
 		return layouts(p.Type(), p.Layout)
 	}

hugolib/site.go

@@ -920,6 +920,26 @@ func (s *Site) RenderPages() error {
 
 	procs := getGoMaxProcs()
 
+	// this cannot be fanned out to multiple Go routines
+	// See issue #1601
+	// TODO(bep): Check the IsRenderable logic.
+	for _, p := range s.Pages {
+		var layouts []string
+		if !p.IsRenderable() {
+			self := "__" + p.TargetPath()
+			_, err := s.Tmpl.New(self).Parse(string(p.Content))
+			if err != nil {
+				results <- err
+				continue
+			}
+			layouts = append(layouts, self)
+		} else {
+			layouts = append(layouts, p.layouts()...)
+			layouts = append(layouts, "_default/single.html")
+		}
+		p.layoutsCalculated = layouts
+	}
+
 	wg := &sync.WaitGroup{}
 
 	for i := 0; i < procs*4; i++ {
@@ -951,22 +971,7 @@ func (s *Site) RenderPages() error {
 func pageRenderer(s *Site, pages <-chan *Page, results chan<- error, wg *sync.WaitGroup) {
 	defer wg.Done()
 	for p := range pages {
-		var layouts []string
+		err := s.renderAndWritePage("page "+p.FullFilePath(), p.TargetPath(), p, s.appendThemeTemplates(p.layouts())...)
-
-		if !p.IsRenderable() {
-			self := "__" + p.TargetPath()
-			_, err := s.Tmpl.New(self).Parse(string(p.Content))
-			if err != nil {
-				results <- err
-				continue
-			}
-			layouts = append(layouts, self)
-		} else {
-			layouts = append(layouts, p.layouts()...)
-			layouts = append(layouts, "_default/single.html")
-		}
-
-		err := s.renderAndWritePage("page "+p.FullFilePath(), p.TargetPath(), p, s.appendThemeTemplates(layouts)...)
 		if err != nil {
 			results <- err
 		}

hugolib/site_test.go

@@ -158,7 +158,7 @@ func TestRenderThing(t *testing.T) {
 		templateName := fmt.Sprintf("foobar%d", i)
 		err = s.addTemplate(templateName, test.template)
 		if err != nil {
-			t.Fatalf("Unable to add template")
+			t.Fatalf("Unable to add template: %s", err)
 		}
 
 		p.Content = template.HTML(p.Content)
@@ -203,7 +203,7 @@ func TestRenderThingOrDefault(t *testing.T) {
 		templateName := fmt.Sprintf("default%d", i)
 		err = s.addTemplate(templateName, test.template)
 		if err != nil {
-			t.Fatalf("Unable to add template")
+			t.Fatalf("Unable to add template: %s", err)
 		}
 
 		var err2 error