Support pages without front matter

* Page without front matter now treated same as a page with empty front matter.
* Test cases added to cover this and repro issue #4320.
* Type safety of front matter code improved.

Fixes #4320

2 files changed, 8 insertions, 11 deletions

diff --git a/parser/frontmatter.go b/parser/frontmatter.go
index ab56b14d1..7560a734a 100644
--- a/parser/frontmatter.go
+++ b/parser/frontmatter.go
@@ -31,7 +31,7 @@ import (
 // FrontmatterType represents a type of frontmatter.
 type FrontmatterType struct {
 	// Parse decodes content into a Go interface.
-	Parse func([]byte) (interface{}, error)
+	Parse func([]byte) (map[string]interface{}, error)
 
 	markstart, markend []byte // starting and ending delimiters
 	includeMark        bool   // include start and end mark in output
@@ -168,7 +168,7 @@ func DetectFrontMatter(mark rune) (f *FrontmatterType) {
 
 // HandleTOMLMetaData unmarshals TOML-encoded datum and returns a Go interface
 // representing the encoded data structure.
-func HandleTOMLMetaData(datum []byte) (interface{}, error) {
+func HandleTOMLMetaData(datum []byte) (map[string]interface{}, error) {
 	m := map[string]interface{}{}
 	datum = removeTOMLIdentifier(datum)
 
@@ -198,7 +198,7 @@ func removeTOMLIdentifier(datum []byte) []byte {
 
 // HandleYAMLMetaData unmarshals YAML-encoded datum and returns a Go interface
 // representing the encoded data structure.
-func HandleYAMLMetaData(datum []byte) (interface{}, error) {
+func HandleYAMLMetaData(datum []byte) (map[string]interface{}, error) {
 	m := map[string]interface{}{}
 	err := yaml.Unmarshal(datum, &m)
 	return m, err
@@ -206,7 +206,7 @@ func HandleYAMLMetaData(datum []byte) (interface{}, error) {
 
 // HandleJSONMetaData unmarshals JSON-encoded datum and returns a Go interface
 // representing the encoded data structure.
-func HandleJSONMetaData(datum []byte) (interface{}, error) {
+func HandleJSONMetaData(datum []byte) (map[string]interface{}, error) {
 	if datum == nil {
 		// Package json returns on error on nil input.
 		// Return an empty map to be consistent with our other supported
@@ -214,13 +214,13 @@ func HandleJSONMetaData(datum []byte) (interface{}, error) {
 		return make(map[string]interface{}), nil
 	}
 
-	var f interface{}
+	var f map[string]interface{}
 	err := json.Unmarshal(datum, &f)
 	return f, err
 }
 
 // HandleOrgMetaData unmarshals org-mode encoded datum and returns a Go
 // interface representing the encoded data structure.
-func HandleOrgMetaData(datum []byte) (interface{}, error) {
+func HandleOrgMetaData(datum []byte) (map[string]interface{}, error) {
 	return goorgeous.OrgHeaders(datum)
 }
diff --git a/parser/page.go b/parser/page.go
index 1537915f4..17378840d 100644
--- a/parser/page.go
+++ b/parser/page.go
@@ -74,7 +74,7 @@ type Page interface {
 	IsRenderable() bool
 
 	// Metadata returns the unmarshalled frontmatter data.
-	Metadata() (interface{}, error)
+	Metadata() (map[string]interface{}, error)
 }
 
 // page implements the Page interface.
@@ -100,16 +100,13 @@ func (p *page) IsRenderable() bool {
 }
 
 // Metadata returns the unmarshalled frontmatter data.
-func (p *page) Metadata() (meta interface{}, err error) {
+func (p *page) Metadata() (meta map[string]interface{}, err error) {
 	frontmatter := p.FrontMatter()
 
 	if len(frontmatter) != 0 {
 		fm := DetectFrontMatter(rune(frontmatter[0]))
 		if fm != nil {
 			meta, err = fm.Parse(frontmatter)
-			if err != nil {
-				return
-			}
 		}
 	}
 	return