Avoid nilpointer on no File on Page

Fixes #5781

3 files changed, 157 insertions, 3 deletions

diff --git a/resources/page/page_generate/generate_page_wrappers.go b/resources/page/page_generate/generate_page_wrappers.go
index 54e1f272e..739d7a00e 100644
--- a/resources/page/page_generate/generate_page_wrappers.go
+++ b/resources/page/page_generate/generate_page_wrappers.go
@@ -63,6 +63,10 @@ func Generate(c *codegen.Inspector) error {
 		return errors.Wrap(err, "failed to generate deprecate wrappers")
 	}
 
+	if err := generateFileIsZeroWrappers(c); err != nil {
+		return errors.Wrap(err, "failed to generate file wrappers")
+	}
+
 	return nil
 }
 
@@ -199,6 +203,68 @@ type pageDeprecated struct {
 	return nil
 }
 
+func generateFileIsZeroWrappers(c *codegen.Inspector) error {
+	filename := filepath.Join(c.ProjectRootDir, packageDir, "zero_file.autogen.go")
+	f, err := os.Create(filename)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+
+	// Generate warnings for zero file access
+
+	warning := func(name string, tp reflect.Type) string {
+		msg := fmt.Sprintf(".File.%s on zero object. Wrap it in if or with: {{ with .File }}{{ .%s }}{{ end }}", name, name)
+
+		return fmt.Sprintf("z.log.Println(%q)", msg)
+	}
+
+	var buff bytes.Buffer
+
+	methods := c.MethodsFromTypes([]reflect.Type{reflect.TypeOf((*source.File)(nil)).Elem()}, nil)
+
+	for _, m := range methods {
+		if m.Name == "IsZero" {
+			continue
+		}
+		fmt.Fprint(&buff, m.DeclarationNamed("zeroFile"))
+		fmt.Fprintln(&buff, " {")
+		fmt.Fprintf(&buff, "\t%s\n", warning(m.Name, m.Owner))
+		if len(m.Out) > 0 {
+			fmt.Fprintln(&buff, "\treturn")
+		}
+		fmt.Fprintln(&buff, "}")
+
+	}
+
+	pkgImports := append(methods.Imports(), "github.com/gohugoio/hugo/helpers", "github.com/gohugoio/hugo/source")
+
+	fmt.Fprintf(f, `%s
+
+package page
+
+%s
+
+// ZeroFile represents a zero value of source.File with warnings if invoked.
+type zeroFile struct {	
+	log *helpers.DistinctLogger 
+}
+
+func NewZeroFile(log *helpers.DistinctLogger) source.File {
+	return zeroFile{log: log}
+}
+
+func (zeroFile) IsZero() bool {
+	return true
+}
+
+%s
+
+`, header, importsString(pkgImports), buff.String())
+
+	return nil
+}
+
 func importsString(imps []string) string {
 	if len(imps) == 0 {
 		return ""
diff --git a/resources/page/pages_sort.go b/resources/page/pages_sort.go
index eb3a28247..7b2a34a6a 100644
--- a/resources/page/pages_sort.go
+++ b/resources/page/pages_sort.go
@@ -51,8 +51,8 @@ var DefaultPageSort = func(p1, p2 Page) bool {
 	if p1.Weight() == p2.Weight() {
 		if p1.Date().Unix() == p2.Date().Unix() {
 			if p1.LinkTitle() == p2.LinkTitle() {
-				if p1.File() == nil || p2.File() == nil {
-					return p1.File() == nil
+				if p1.File().IsZero() || p2.File().IsZero() {
+					return p1.File().IsZero()
 				}
 				return p1.File().Filename() < p2.File().Filename()
 			}
@@ -77,7 +77,7 @@ var languagePageSort = func(p1, p2 Page) bool {
 	if p1.Language().Weight == p2.Language().Weight {
 		if p1.Date().Unix() == p2.Date().Unix() {
 			if p1.LinkTitle() == p2.LinkTitle() {
-				if p1.File() != nil && p2.File() != nil {
+				if !p1.File().IsZero() && !p2.File().IsZero() {
 					return p1.File().Filename() < p2.File().Filename()
 				}
 			}
diff --git a/resources/page/zero_file.autogen.go b/resources/page/zero_file.autogen.go
new file mode 100644
index 000000000..eec1dd66d
--- /dev/null
+++ b/resources/page/zero_file.autogen.go
@@ -0,0 +1,88 @@
+// Copyright 2019 The Hugo Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// This file is autogenerated.
+
+package page
+
+import (
+	"github.com/gohugoio/hugo/helpers"
+	"github.com/gohugoio/hugo/source"
+	"os"
+)
+
+// ZeroFile represents a zero value of source.File with warnings if invoked.
+type zeroFile struct {
+	log *helpers.DistinctLogger
+}
+
+func NewZeroFile(log *helpers.DistinctLogger) source.File {
+	return zeroFile{log: log}
+}
+
+func (zeroFile) IsZero() bool {
+	return true
+}
+
+func (z zeroFile) Path() (o0 string) {
+	z.log.Println(".File.Path on zero object. Wrap it in if or with: {{ with .File }}{{ .Path }}{{ end }}")
+	return
+}
+func (z zeroFile) Section() (o0 string) {
+	z.log.Println(".File.Section on zero object. Wrap it in if or with: {{ with .File }}{{ .Section }}{{ end }}")
+	return
+}
+func (z zeroFile) Lang() (o0 string) {
+	z.log.Println(".File.Lang on zero object. Wrap it in if or with: {{ with .File }}{{ .Lang }}{{ end }}")
+	return
+}
+func (z zeroFile) Filename() (o0 string) {
+	z.log.Println(".File.Filename on zero object. Wrap it in if or with: {{ with .File }}{{ .Filename }}{{ end }}")
+	return
+}
+func (z zeroFile) Dir() (o0 string) {
+	z.log.Println(".File.Dir on zero object. Wrap it in if or with: {{ with .File }}{{ .Dir }}{{ end }}")
+	return
+}
+func (z zeroFile) Extension() (o0 string) {
+	z.log.Println(".File.Extension on zero object. Wrap it in if or with: {{ with .File }}{{ .Extension }}{{ end }}")
+	return
+}
+func (z zeroFile) Ext() (o0 string) {
+	z.log.Println(".File.Ext on zero object. Wrap it in if or with: {{ with .File }}{{ .Ext }}{{ end }}")
+	return
+}
+func (z zeroFile) LogicalName() (o0 string) {
+	z.log.Println(".File.LogicalName on zero object. Wrap it in if or with: {{ with .File }}{{ .LogicalName }}{{ end }}")
+	return
+}
+func (z zeroFile) BaseFileName() (o0 string) {
+	z.log.Println(".File.BaseFileName on zero object. Wrap it in if or with: {{ with .File }}{{ .BaseFileName }}{{ end }}")
+	return
+}
+func (z zeroFile) TranslationBaseName() (o0 string) {
+	z.log.Println(".File.TranslationBaseName on zero object. Wrap it in if or with: {{ with .File }}{{ .TranslationBaseName }}{{ end }}")
+	return
+}
+func (z zeroFile) ContentBaseName() (o0 string) {
+	z.log.Println(".File.ContentBaseName on zero object. Wrap it in if or with: {{ with .File }}{{ .ContentBaseName }}{{ end }}")
+	return
+}
+func (z zeroFile) UniqueID() (o0 string) {
+	z.log.Println(".File.UniqueID on zero object. Wrap it in if or with: {{ with .File }}{{ .UniqueID }}{{ end }}")
+	return
+}
+func (z zeroFile) FileInfo() (o0 os.FileInfo) {
+	z.log.Println(".File.FileInfo on zero object. Wrap it in if or with: {{ with .File }}{{ .FileInfo }}{{ end }}")
+	return
+}