Avoid nilpointer on no File on Page

Fixes #5781

7 files changed, 24 insertions, 12 deletions

diff --git a/hugolib/hugo_sites.go b/hugolib/hugo_sites.go
index 0c79f4bdb..9fe2a5bdb 100644
--- a/hugolib/hugo_sites.go
+++ b/hugolib/hugo_sites.go
@@ -577,7 +577,7 @@ func (cfg *BuildCfg) shouldRender(p *pageState) bool {
 		return true
 	}
 
-	if cfg.whatChanged != nil && p.File() != nil {
+	if cfg.whatChanged != nil && !p.File().IsZero() {
 		return cfg.whatChanged.files[p.File().Filename()]
 	}
 
diff --git a/hugolib/page.go b/hugolib/page.go
index 576342cfa..99b771eee 100644
--- a/hugolib/page.go
+++ b/hugolib/page.go
@@ -236,7 +236,7 @@ func (p *pageState) TranslationKey() string {
 	p.translationKeyInit.Do(func() {
 		if p.m.translationKey != "" {
 			p.translationKey = p.Kind() + "/" + p.m.translationKey
-		} else if p.IsPage() && p.File() != nil {
+		} else if p.IsPage() && !p.File().IsZero() {
 			p.translationKey = path.Join(p.Kind(), filepath.ToSlash(p.File().Dir()), p.File().TranslationBaseName())
 		} else if p.IsNode() {
 			p.translationKey = path.Join(p.Kind(), p.SectionsPath())
@@ -462,7 +462,7 @@ func (p *pageState) Render(layout ...string) template.HTML {
 func (p *pageState) wrapError(err error) error {
 
 	var filename string
-	if p.File() != nil {
+	if !p.File().IsZero() {
 		filename = p.File().Filename()
 	}
 
@@ -665,7 +665,7 @@ func (p *pageState) parseError(err error, input []byte, offset int) error {
 }
 
 func (p *pageState) pathOrTitle() string {
-	if p.File() != nil {
+	if !p.File().IsZero() {
 		return p.File().Filename()
 	}
 
@@ -763,7 +763,7 @@ func (p *pageState) sortParentSections() {
 // For pages that do not (sections witout content page etc.), it returns the
 // virtual path, consistent with where you would add a source file.
 func (p *pageState) sourceRef() string {
-	if p.File() != nil {
+	if !p.File().IsZero() {
 		sourcePath := p.File().Path()
 		if sourcePath != "" {
 			return "/" + filepath.ToSlash(sourcePath)
diff --git a/hugolib/page__meta.go b/hugolib/page__meta.go
index 8532f5016..2c6b0a85d 100644
--- a/hugolib/page__meta.go
+++ b/hugolib/page__meta.go
@@ -222,7 +222,7 @@ func (p *pageMeta) Params() map[string]interface{} {
 }
 
 func (p *pageMeta) Path() string {
-	if p.File() != nil {
+	if !p.File().IsZero() {
 		return p.File().Path()
 	}
 	return p.SectionsPath()
@@ -256,7 +256,7 @@ func (p *pageMeta) Section() string {
 		return p.sections[0]
 	}
 
-	if p.File() != nil {
+	if !p.File().IsZero() {
 		return p.File().Section()
 	}
 
@@ -536,8 +536,8 @@ func (pm *pageMeta) setMetadata(p *pageState, frontmatter map[string]interface{}
 
 func (p *pageMeta) applyDefaultValues() error {
 	if p.markup == "" {
-		if p.File() != nil {
-			// Fall back to {file extension
+		if !p.File().IsZero() {
+			// Fall back to file extension
 			p.markup = helpers.GuessType(p.File().Ext())
 		}
 		if p.markup == "" {
diff --git a/hugolib/page__new.go b/hugolib/page__new.go
index 0f419b5da..0ac14a5e8 100644
--- a/hugolib/page__new.go
+++ b/hugolib/page__new.go
@@ -95,6 +95,10 @@ func newPageBase(metaProvider *pageMeta) (*pageState, error) {
 }
 
 func newPageFromMeta(metaProvider *pageMeta) (*pageState, error) {
+	if metaProvider.f == nil {
+		metaProvider.f = page.NewZeroFile(metaProvider.s.DistinctWarningLog)
+	}
+
 	ps, err := newPageBase(metaProvider)
 	if err != nil {
 		return nil, err
diff --git a/hugolib/page__paths.go b/hugolib/page__paths.go
index 0a5dad5ef..8bc7a7535 100644
--- a/hugolib/page__paths.go
+++ b/hugolib/page__paths.go
@@ -99,7 +99,7 @@ func createTargetPathDescriptor(s *Site, p page.Page, pm *pageMeta) (page.Target
 
 	d := s.Deps
 
-	if p.File() != nil {
+	if !p.File().IsZero() {
 		dir = p.File().Dir()
 		baseName = p.File().TranslationBaseName()
 	}
diff --git a/hugolib/page_test.go b/hugolib/page_test.go
index 5e9ac696c..1e362e0dc 100644
--- a/hugolib/page_test.go
+++ b/hugolib/page_test.go
@@ -18,6 +18,8 @@ import (
 	"html/template"
 	"os"
 
+	"github.com/gohugoio/hugo/common/loggers"
+
 	"path/filepath"
 	"strings"
 	"testing"
@@ -1166,6 +1168,12 @@ Content:{{ .Content }}
 
 }
 
+// https://github.com/gohugoio/hugo/issues/5781
+func TestPageWithZeroFile(t *testing.T) {
+	newTestSitesBuilder(t).WithLogger(loggers.NewWarningLogger()).WithSimpleConfigFile().
+		WithTemplatesAdded("index.html", "{{ .File.Filename }}{{ with .File }}{{ .Dir }}{{ end }}").Build(BuildCfg{})
+}
+
 func TestShouldBuild(t *testing.T) {
 	t.Parallel()
 	var past = time.Date(2009, 11, 17, 20, 34, 58, 651387237, time.UTC)
diff --git a/hugolib/site.go b/hugolib/site.go
index 145ae2d49..1bf2d639c 100644
--- a/hugolib/site.go
+++ b/hugolib/site.go
@@ -789,11 +789,11 @@ func (s *siteRefLinker) refLink(ref string, source interface{}, relative bool, o
 	if refURL.Fragment != "" {
 		_ = target
 		link = link + "#" + refURL.Fragment
-		if pctx, ok := target.(pageContext); ok && target.File() != nil && !pctx.getRenderingConfig().PlainIDAnchors {
+		if pctx, ok := target.(pageContext); ok && !target.File().IsZero() && !pctx.getRenderingConfig().PlainIDAnchors {
 			if refURL.Path != "" {
 				link = link + ":" + target.File().UniqueID()
 			}
-		} else if pctx, ok := p.(pageContext); ok && p.File() != nil && !pctx.getRenderingConfig().PlainIDAnchors {
+		} else if pctx, ok := p.(pageContext); ok && !p.File().IsZero() && !pctx.getRenderingConfig().PlainIDAnchors {
 			link = link + ":" + p.File().UniqueID()
 		}