hugolib: Fix possible .Content cut

There have been one report of a site with truncated `.Content` after the Hugo `0.40.1` release.

This commit fixes this so that race should not be possible anymore. It also adds a stress test with focus on content rendering and multiple output formats.

Fixes #4706

8 files changed, 190 insertions, 55 deletions

diff --git a/hugolib/hugo_sites.go b/hugolib/hugo_sites.go
index a5bb664c0..e3defe974 100644
--- a/hugolib/hugo_sites.go
+++ b/hugolib/hugo_sites.go
@@ -559,14 +559,22 @@ func (h *HugoSites) setupTranslations() {
 	}
 }
 
-func (s *Site) preparePagesForRender(start bool) {
+func (s *Site) preparePagesForRender(start bool) error {
 	for _, p := range s.Pages {
 		p.setContentInit(start)
+		if err := p.initMainOutputFormat(); err != nil {
+			return err
+		}
 	}
 
 	for _, p := range s.headlessPages {
 		p.setContentInit(start)
+		if err := p.initMainOutputFormat(); err != nil {
+			return err
+		}
 	}
+
+	return nil
 }
 
 // Pages returns all pages for all sites.
diff --git a/hugolib/hugo_sites_build.go b/hugolib/hugo_sites_build.go
index 0421c7925..e1e4a6056 100644
--- a/hugolib/hugo_sites_build.go
+++ b/hugolib/hugo_sites_build.go
@@ -234,7 +234,9 @@ func (h *HugoSites) render(config *BuildCfg) error {
 
 				isRenderingSite := s == s2
 
-				s2.preparePagesForRender(isRenderingSite && i == 0)
+				if err := s2.preparePagesForRender(isRenderingSite && i == 0); err != nil {
+					return err
+				}
 
 			}
 
diff --git a/hugolib/hugo_sites_build_test.go b/hugolib/hugo_sites_build_test.go
index 87eb2cb29..4192580bd 100644
--- a/hugolib/hugo_sites_build_test.go
+++ b/hugolib/hugo_sites_build_test.go
@@ -734,6 +734,119 @@ func TestChangeDefaultLanguage(t *testing.T) {
 	b.AssertFileContent("public/sect/doc2/index.html", "Single", "Hello")
 }
 
+// https://github.com/gohugoio/hugo/issues/4706
+func TestContentStressTest(t *testing.T) {
+	b := newTestSitesBuilder(t)
+
+	numPages := 500
+
+	contentTempl := `
+---
+%s
+title: %q
+weight: %d
+multioutput: %t
+---
+
+# Header
+
+CONTENT
+
+The End.
+`
+
+	contentTempl = strings.Replace(contentTempl, "CONTENT", strings.Repeat(`
+	
+## Another header
+
+Some text. Some more text.
+
+`, 100), -1)
+
+	var content []string
+	defaultOutputs := `outputs: ["html", "json", "rss" ]`
+
+	for i := 1; i <= numPages; i++ {
+		outputs := defaultOutputs
+		multioutput := true
+		if i%3 == 0 {
+			outputs = `outputs: ["json"]`
+			multioutput = false
+		}
+		section := "s1"
+		if i%10 == 0 {
+			section = "s2"
+		}
+		content = append(content, []string{fmt.Sprintf("%s/page%d.md", section, i), fmt.Sprintf(contentTempl, outputs, fmt.Sprintf("Title %d", i), i, multioutput)}...)
+	}
+
+	content = append(content, []string{"_index.md", fmt.Sprintf(contentTempl, defaultOutputs, fmt.Sprintf("Home %d", 0), 0, true)}...)
+	content = append(content, []string{"s1/_index.md", fmt.Sprintf(contentTempl, defaultOutputs, fmt.Sprintf("S %d", 1), 1, true)}...)
+	content = append(content, []string{"s2/_index.md", fmt.Sprintf(contentTempl, defaultOutputs, fmt.Sprintf("S %d", 2), 2, true)}...)
+
+	b.WithSimpleConfigFile()
+	b.WithTemplates("layouts/_default/single.html", `Single: {{ .Content }}`)
+	b.WithTemplates("layouts/_default/myview.html", `View: {{ len .Content }}`)
+	b.WithTemplates("layouts/_default/single.json", `Single JSON: {{ .Content }}`)
+	b.WithTemplates("layouts/_default/list.html", `
+Page: {{ .Paginator.PageNumber }}
+P: {{ path.Join .Path }}
+List: {{ len .Paginator.Pages }}|List Content: {{ len .Content }}
+{{ $shuffled :=  where .Site.RegularPages "Params.multioutput" true | shuffle }}
+{{ $first5 := $shuffled | first 5 }}
+L1: {{ len .Site.RegularPages }} L2: {{ len $first5 }}
+{{ range $i, $e := $first5 }}
+Render {{ $i }}: {{ .Render "myview" }}
+{{ end }}
+END
+`)
+
+	b.WithContent(content...)
+
+	b.CreateSites().Build(BuildCfg{})
+
+	contentMatchers := []string{"<h2 id=\"another-header\">Another header</h2>", "<h2 id=\"another-header-99\">Another header</h2>", "<p>The End.</p>"}
+
+	for i := 1; i <= numPages; i++ {
+		if i%3 != 0 {
+			section := "s1"
+			if i%10 == 0 {
+				section = "s2"
+			}
+			checkContent(b, fmt.Sprintf("public/%s/page%d/index.html", section, i), 8343, contentMatchers...)
+		}
+	}
+
+	for i := 1; i <= numPages; i++ {
+		section := "s1"
+		if i%10 == 0 {
+			section = "s2"
+		}
+		checkContent(b, fmt.Sprintf("public/%s/page%d/index.json", section, i), 8348, contentMatchers...)
+	}
+
+	checkContent(b, "public/s1/index.html", 184, "P: s1/_index.md\nList: 10|List Content: 8335\n\n\nL1: 500 L2: 5\n\nRender 0: View: 8335\n\nRender 1: View: 8335\n\nRender 2: View: 8335\n\nRender 3: View: 8335\n\nRender 4: View: 8335\n\nEND\n")
+	checkContent(b, "public/s2/index.html", 184, "P: s2/_index.md\nList: 10|List Content: 8335", "Render 4: View: 8335\n\nEND")
+	checkContent(b, "public/index.html", 181, "P: _index.md\nList: 10|List Content: 8335", "4: View: 8335\n\nEND")
+
+	// Chek paginated pages
+	for i := 2; i <= 9; i++ {
+		checkContent(b, fmt.Sprintf("public/page/%d/index.html", i), 181, fmt.Sprintf("Page: %d", i), "Content: 8335\n\n\nL1: 500 L2: 5\n\nRender 0: View: 8335", "Render 4: View: 8335\n\nEND")
+	}
+}
+
+func checkContent(s *sitesBuilder, filename string, length int, matches ...string) {
+	content := readDestination(s.T, s.Fs, filename)
+	for _, match := range matches {
+		if !strings.Contains(content, match) {
+			s.Fatalf("No match for %q in content for %s\n%q", match, filename, content)
+		}
+	}
+	if len(content) != length {
+		s.Fatalf("got %d expected %d", len(content), length)
+	}
+}
+
 func TestTableOfContentsInShortcodes(t *testing.T) {
 	t.Parallel()
 
diff --git a/hugolib/page.go b/hugolib/page.go
index 2e008ece9..6e0f2b86f 100644
--- a/hugolib/page.go
+++ b/hugolib/page.go
@@ -416,7 +416,6 @@ type pageInit struct {
 	languageInit        sync.Once
 	pageMenusInit       sync.Once
 	pageMetaInit        sync.Once
-	pageOutputInit      sync.Once
 	renderingConfigInit sync.Once
 	withoutContentInit  sync.Once
 }
@@ -1178,6 +1177,24 @@ func (p *Page) subResourceTargetPathFactory(base string) string {
 	return path.Join(p.relTargetPathBase, base)
 }
 
+func (p *Page) initMainOutputFormat() error {
+	if p.mainPageOutput != nil {
+		return nil
+	}
+
+	outFormat := p.outputFormats[0]
+	pageOutput, err := newPageOutput(p, false, false, outFormat)
+
+	if err != nil {
+		return fmt.Errorf("Failed to create output page for type %q for page %q: %s", outFormat.Name, p.pathOrTitle(), err)
+	}
+
+	p.mainPageOutput = pageOutput
+
+	return nil
+
+}
+
 func (p *Page) setContentInit(start bool) error {
 
 	if start {
@@ -1962,12 +1979,17 @@ func (p *Page) updatePageDates() {
 
 // copy creates a copy of this page with the lazy sync.Once vars reset
 // so they will be evaluated again, for word count calculations etc.
-func (p *Page) copy() *Page {
+func (p *Page) copy(initContent bool) *Page {
 	p.contentInitMu.Lock()
 	c := *p
 	p.contentInitMu.Unlock()
 	c.pageInit = &pageInit{}
-	c.pageContentInit = &pageContentInit{}
+	if initContent {
+		if len(p.outputFormats) < 2 {
+			panic(fmt.Sprintf("programming error: page %q should not need to rebuild content as it has only %d outputs", p.Path(), len(p.outputFormats)))
+		}
+		c.pageContentInit = &pageContentInit{}
+	}
 	return &c
 }
 
diff --git a/hugolib/page_output.go b/hugolib/page_output.go
index 0a51e72f7..5893bc172 100644
--- a/hugolib/page_output.go
+++ b/hugolib/page_output.go
@@ -55,7 +55,7 @@ func (p *PageOutput) targetPath(addends ...string) (string, error) {
 	return tp, nil
 }
 
-func newPageOutput(p *Page, createCopy bool, f output.Format) (*PageOutput, error) {
+func newPageOutput(p *Page, createCopy, initContent bool, f output.Format) (*PageOutput, error) {
 	// TODO(bep) This is only needed for tests and we should get rid of it.
 	if p.targetPathDescriptorPrototype == nil {
 		if err := p.initPaths(); err != nil {
@@ -64,7 +64,7 @@ func newPageOutput(p *Page, createCopy bool, f output.Format) (*PageOutput, erro
 	}
 
 	if createCopy {
-		p = p.copy()
+		p = p.copy(initContent)
 	}
 
 	td, err := p.createTargetPathDescriptor(f)
@@ -82,8 +82,8 @@ func newPageOutput(p *Page, createCopy bool, f output.Format) (*PageOutput, erro
 
 // copy creates a copy of this PageOutput with the lazy sync.Once vars reset
 // so they will be evaluated again, for word count calculations etc.
-func (p *PageOutput) copyWithFormat(f output.Format) (*PageOutput, error) {
-	c, err := newPageOutput(p.Page, true, f)
+func (p *PageOutput) copyWithFormat(f output.Format, initContent bool) (*PageOutput, error) {
+	c, err := newPageOutput(p.Page, true, initContent, f)
 	if err != nil {
 		return nil, err
 	}
@@ -92,7 +92,7 @@ func (p *PageOutput) copyWithFormat(f output.Format) (*PageOutput, error) {
 }
 
 func (p *PageOutput) copy() (*PageOutput, error) {
-	return p.copyWithFormat(p.outputFormat)
+	return p.copyWithFormat(p.outputFormat, false)
 }
 
 func (p *PageOutput) layouts(layouts ...string) ([]string, error) {
@@ -142,24 +142,6 @@ func (p *PageOutput) Render(layout ...string) template.HTML {
 }
 
 func (p *Page) Render(layout ...string) template.HTML {
-	p.pageOutputInit.Do(func() {
-		if p.mainPageOutput != nil {
-			return
-		}
-		// If Render is called in a range loop, the page output isn't available.
-		// So, create one.
-		outFormat := p.outputFormats[0]
-		pageOutput, err := newPageOutput(p, true, outFormat)
-
-		if err != nil {
-			p.s.Log.ERROR.Printf("Failed to create output page for type %q for page %q: %s", outFormat.Name, p.pathOrTitle(), err)
-			return
-		}
-
-		p.mainPageOutput = pageOutput
-
-	})
-
 	return p.mainPageOutput.Render(layout...)
 }
 
diff --git a/hugolib/pagination_test.go b/hugolib/pagination_test.go
index edfac3f3e..61668c3df 100644
--- a/hugolib/pagination_test.go
+++ b/hugolib/pagination_test.go
@@ -279,8 +279,8 @@ func doTestPaginator(t *testing.T, useViper bool) {
 	require.NoError(t, err)
 
 	pages := createTestPages(s, 12)
-	n1, _ := newPageOutput(s.newHomePage(), false, output.HTMLFormat)
-	n2, _ := newPageOutput(s.newHomePage(), false, output.HTMLFormat)
+	n1, _ := newPageOutput(s.newHomePage(), false, false, output.HTMLFormat)
+	n2, _ := newPageOutput(s.newHomePage(), false, false, output.HTMLFormat)
 	n1.Data["Pages"] = pages
 
 	var paginator1 *Pager
@@ -306,7 +306,7 @@ func doTestPaginator(t *testing.T, useViper bool) {
 	require.Equal(t, paginator1, samePaginator)
 
 	pp, _ := s.NewPage("test")
-	p, _ := newPageOutput(pp, false, output.HTMLFormat)
+	p, _ := newPageOutput(pp, false, false, output.HTMLFormat)
 
 	_, err = p.Paginator()
 	require.NotNil(t, err)
@@ -315,7 +315,7 @@ func doTestPaginator(t *testing.T, useViper bool) {
 func TestPaginatorWithNegativePaginate(t *testing.T) {
 	t.Parallel()
 	s := newTestSite(t, "paginate", -1)
-	n1, _ := newPageOutput(s.newHomePage(), false, output.HTMLFormat)
+	n1, _ := newPageOutput(s.newHomePage(), false, false, output.HTMLFormat)
 	_, err := n1.Paginator()
 	require.Error(t, err)
 }
@@ -378,8 +378,8 @@ func doTestPaginate(t *testing.T, useViper bool) {
 	}
 
 	pages := createTestPages(s, 6)
-	n1, _ := newPageOutput(s.newHomePage(), false, output.HTMLFormat)
-	n2, _ := newPageOutput(s.newHomePage(), false, output.HTMLFormat)
+	n1, _ := newPageOutput(s.newHomePage(), false, false, output.HTMLFormat)
+	n2, _ := newPageOutput(s.newHomePage(), false, false, output.HTMLFormat)
 
 	var paginator1, paginator2 *Pager
 
@@ -404,7 +404,7 @@ func doTestPaginate(t *testing.T, useViper bool) {
 	require.Equal(t, paginator2, paginator1.Next())
 
 	pp, err := s.NewPage("test")
-	p, _ := newPageOutput(pp, false, output.HTMLFormat)
+	p, _ := newPageOutput(pp, false, false, output.HTMLFormat)
 
 	_, err = p.Paginate(pages)
 	require.NotNil(t, err)
@@ -413,7 +413,7 @@ func doTestPaginate(t *testing.T, useViper bool) {
 func TestInvalidOptions(t *testing.T) {
 	t.Parallel()
 	s := newTestSite(t)
-	n1, _ := newPageOutput(s.newHomePage(), false, output.HTMLFormat)
+	n1, _ := newPageOutput(s.newHomePage(), false, false, output.HTMLFormat)
 
 	_, err := n1.Paginate(createTestPages(s, 1), 1, 2)
 	require.NotNil(t, err)
@@ -431,7 +431,7 @@ func TestPaginateWithNegativePaginate(t *testing.T) {
 	s, err := NewSiteForCfg(deps.DepsCfg{Cfg: cfg, Fs: fs})
 	require.NoError(t, err)
 
-	n, _ := newPageOutput(s.newHomePage(), false, output.HTMLFormat)
+	n, _ := newPageOutput(s.newHomePage(), false, false, output.HTMLFormat)
 
 	_, err = n.Paginate(createTestPages(s, 2))
 	require.NotNil(t, err)
@@ -458,8 +458,8 @@ func TestPaginatePages(t *testing.T) {
 func TestPaginatorFollowedByPaginateShouldFail(t *testing.T) {
 	t.Parallel()
 	s := newTestSite(t, "paginate", 10)
-	n1, _ := newPageOutput(s.newHomePage(), false, output.HTMLFormat)
-	n2, _ := newPageOutput(s.newHomePage(), false, output.HTMLFormat)
+	n1, _ := newPageOutput(s.newHomePage(), false, false, output.HTMLFormat)
+	n2, _ := newPageOutput(s.newHomePage(), false, false, output.HTMLFormat)
 
 	_, err := n1.Paginator()
 	require.Nil(t, err)
@@ -475,8 +475,8 @@ func TestPaginateFollowedByDifferentPaginateShouldFail(t *testing.T) {
 	t.Parallel()
 	s := newTestSite(t, "paginate", 10)
 
-	n1, _ := newPageOutput(s.newHomePage(), false, output.HTMLFormat)
-	n2, _ := newPageOutput(s.newHomePage(), false, output.HTMLFormat)
+	n1, _ := newPageOutput(s.newHomePage(), false, false, output.HTMLFormat)
+	n2, _ := newPageOutput(s.newHomePage(), false, false, output.HTMLFormat)
 
 	p1 := createTestPages(s, 2)
 	p2 := createTestPages(s, 10)
diff --git a/hugolib/site_render.go b/hugolib/site_render.go
index e9d2f0183..e837d9f0b 100644
--- a/hugolib/site_render.go
+++ b/hugolib/site_render.go
@@ -73,7 +73,7 @@ func headlessPagesPublisher(s *Site, wg *sync.WaitGroup) {
 			// Avoid double work.
 			continue
 		}
-		pageOutput, err := newPageOutput(page, false, outFormat)
+		pageOutput, err := newPageOutput(page, false, false, outFormat)
 		if err == nil {
 			page.mainPageOutput = pageOutput
 			err = pageOutput.renderResources()
@@ -92,28 +92,29 @@ func pageRenderer(s *Site, pages <-chan *Page, results chan<- error, wg *sync.Wa
 
 		for i, outFormat := range page.outputFormats {
 
+			if outFormat != page.s.rc.Format {
+				// Will be rendered  ... later.
+				continue
+			}
+
 			var (
 				pageOutput *PageOutput
 				err        error
 			)
 
 			if i == 0 {
-				pageOutput, err = newPageOutput(page, false, outFormat)
-				page.mainPageOutput = pageOutput
+				pageOutput = page.mainPageOutput
+			} else {
+				pageOutput, err = page.mainPageOutput.copyWithFormat(outFormat, true)
 			}
 
-			if outFormat != page.s.rc.Format {
-				// Will be rendered  ... later.
+			if err != nil {
+				s.Log.ERROR.Printf("Failed to create output page for type %q for page %q: %s", outFormat.Name, page, err)
 				continue
 			}
 
 			if pageOutput == nil {
-				pageOutput, err = page.mainPageOutput.copyWithFormat(outFormat)
-			}
-
-			if err != nil {
-				s.Log.ERROR.Printf("Failed to create output page for type %q for page %q: %s", outFormat.Name, page, err)
-				continue
+				panic("no pageOutput")
 			}
 
 			// We only need to re-publish the resources if the output format is different
@@ -291,7 +292,7 @@ func (s *Site) render404() error {
 	htmlOut := output.HTMLFormat
 	htmlOut.BaseName = "404"
 
-	pageOutput, err := newPageOutput(p, false, htmlOut)
+	pageOutput, err := newPageOutput(p, false, false, htmlOut)
 	if err != nil {
 		return err
 	}
@@ -373,7 +374,7 @@ func (s *Site) renderRobotsTXT() error {
 
 	rLayouts := []string{"robots.txt", "_default/robots.txt", "_internal/_default/robots.txt"}
 
-	pageOutput, err := newPageOutput(p, false, output.RobotsTxtFormat)
+	pageOutput, err := newPageOutput(p, false, false, output.RobotsTxtFormat)
 	if err != nil {
 		return err
 	}
diff --git a/hugolib/testhelpers_test.go b/hugolib/testhelpers_test.go
index 5300eee22..62fe3860a 100644
--- a/hugolib/testhelpers_test.go
+++ b/hugolib/testhelpers_test.go
@@ -39,6 +39,8 @@ type sitesBuilder struct {
 	Fs  *hugofs.Fs
 	T   testing.TB
 
+	logger *jww.Notepad
+
 	dumper litter.Options
 
 	// Aka the Hugo server mode.
@@ -88,6 +90,11 @@ func (s *sitesBuilder) Running() *sitesBuilder {
 	return s
 }
 
+func (s *sitesBuilder) WithLogger(logger *jww.Notepad) *sitesBuilder {
+	s.logger = logger
+	return s
+}
+
 func (s *sitesBuilder) WithWorkingDir(dir string) *sitesBuilder {
 	s.workingDir = dir
 	return s
@@ -282,7 +289,7 @@ func (s *sitesBuilder) CreateSites() *sitesBuilder {
 		s.Cfg = cfg
 	}
 
-	sites, err := NewHugoSites(deps.DepsCfg{Fs: s.Fs, Cfg: s.Cfg, Running: s.running})
+	sites, err := NewHugoSites(deps.DepsCfg{Fs: s.Fs, Cfg: s.Cfg, Logger: s.logger, Running: s.running})
 	if err != nil {
 		s.Fatalf("Failed to create sites: %s", err)
 	}