hugolib: Cache the value of Page's RelPermalink

hugolib/page.go

@@ -190,6 +190,7 @@ type Page struct {
 
 	URLPath
 	permalink    *url.URL
+	relPermalink string
 
 	paginator *Pager
 
@@ -213,6 +214,7 @@ type pageInit struct {
 	plainWordsInit      sync.Once
 	renderingConfigInit sync.Once
 	pageURLInit         sync.Once
+	relPermalinkInit    sync.Once
 }
 
 // IsNode returns whether this is an item of one of the list types in Hugo,
@@ -927,6 +929,7 @@ func (p *Page) URL() string {
 }
 
 func (p *Page) RelPermalink() string {
+	p.relPermalinkInit.Do(func() {
 		link := p.getPermalink()
 
 		if p.s.Info.canonifyURLs {
@@ -934,7 +937,7 @@ func (p *Page) RelPermalink() string {
 			// have to return the URL relative from baseURL
 			relpath, err := helpers.GetRelativePath(link.String(), string(p.Site.BaseURL))
 			if err != nil {
-			return ""
+				return
 			}
 
 			relpath = filepath.ToSlash(relpath)
@@ -947,14 +950,18 @@ func (p *Page) RelPermalink() string {
 				relpath = "/" + relpath
 			}
 
-		return relpath
+			p.relPermalink = relpath
+			return
 		}
 
 		link.Scheme = ""
 		link.Host = ""
 		link.User = nil
 		link.Opaque = ""
-	return link.String()
+		p.relPermalink = link.String()
+	})
+
+	return p.relPermalink
 }
 
 var ErrHasDraftAndPublished = errors.New("both draft and published parameters were found in page's frontmatter")