Add Lastmod field

Create new field in Node
Update Page to look for lastmod field in the front matter. If not present, then assign Date to Lastmod
Update Site, to assign a value to Lastmod (based on the same logic used for Date)

Fixes #733

3 files changed, 18 insertions, 0 deletions

diff --git a/hugolib/node.go b/hugolib/node.go
index 9be215058..7606e8896 100644
--- a/hugolib/node.go
+++ b/hugolib/node.go
@@ -30,6 +30,7 @@ type Node struct {
 	Keywords    []string
 	Params      map[string]interface{}
 	Date        time.Time
+	Lastmod     time.Time
 	Sitemap     Sitemap
 	URLPath
 	paginator     *Pager
diff --git a/hugolib/page.go b/hugolib/page.go
index 56a9ff16a..fd3bddcdb 100644
--- a/hugolib/page.go
+++ b/hugolib/page.go
@@ -473,6 +473,11 @@ func (p *Page) update(f interface{}) error {
 			if err != nil {
 				jww.ERROR.Printf("Failed to parse date '%v' in page %s", v, p.File.Path())
 			}
+		case "lastmod":
+			p.Lastmod, err = cast.ToTimeE(v)
+			if err != nil {
+				jww.ERROR.Printf("Failed to parse lastmod '%v' in page %s", v, p.File.Path())
+			}
 		case "publishdate", "pubdate":
 			p.PublishDate, err = cast.ToTimeE(v)
 			if err != nil {
@@ -524,6 +529,11 @@ func (p *Page) update(f interface{}) error {
 			}
 		}
 	}
+
+	if p.Lastmod.IsZero() {
+		p.Lastmod = p.Date
+	}
+
 	return nil
 
 }
diff --git a/hugolib/site.go b/hugolib/site.go
index 2018df4bb..45912abcd 100644
--- a/hugolib/site.go
+++ b/hugolib/site.go
@@ -1065,6 +1065,7 @@ func (s *Site) newTaxonomyNode(t taxRenderInfo) (*Node, string) {
 	s.setURLs(n, base)
 	if len(t.pages) > 0 {
 		n.Date = t.pages[0].Page.Date
+		n.Lastmod = t.pages[0].Page.Lastmod
 	}
 	n.Data[t.singular] = t.pages
 	n.Data["Singular"] = t.singular
@@ -1110,6 +1111,7 @@ func taxonomyRenderer(s *Site, taxes <-chan taxRenderInfo, results chan<- error,
 				taxonomyPagerNode.paginator = pager
 				if pager.TotalPages() > 0 {
 					taxonomyPagerNode.Date = pager.Pages()[0].Date
+					taxonomyPagerNode.Lastmod = pager.Pages()[0].Lastmod
 				}
 				pageNumber := i + 1
 				htmlBase := fmt.Sprintf("/%s/%s/%d", base, paginatePath, pageNumber)
@@ -1168,6 +1170,7 @@ func (s *Site) newSectionListNode(section string, data WeightedPages) *Node {
 	}
 	s.setURLs(n, section)
 	n.Date = data[0].Page.Date
+	n.Lastmod = data[0].Page.Lastmod
 	n.Data["Pages"] = data.Pages()
 
 	return n
@@ -1205,6 +1208,7 @@ func (s *Site) RenderSectionLists() error {
 				sectionPagerNode.paginator = pager
 				if pager.TotalPages() > 0 {
 					sectionPagerNode.Date = pager.Pages()[0].Date
+					sectionPagerNode.Lastmod = pager.Pages()[0].Lastmod
 				}
 				pageNumber := i + 1
 				htmlBase := fmt.Sprintf("/%s/%s/%d", section, paginatePath, pageNumber)
@@ -1262,6 +1266,7 @@ func (s *Site) RenderHomePage() error {
 			homePagerNode.paginator = pager
 			if pager.TotalPages() > 0 {
 				homePagerNode.Date = pager.Pages()[0].Date
+				homePagerNode.Lastmod = pager.Pages()[0].Lastmod
 			}
 			pageNumber := i + 1
 			htmlBase := fmt.Sprintf("/%s/%d", paginatePath, pageNumber)
@@ -1282,6 +1287,7 @@ func (s *Site) RenderHomePage() error {
 		n.Data["Pages"] = s.Pages[:high]
 		if len(s.Pages) > 0 {
 			n.Date = s.Pages[0].Date
+			n.Lastmod = s.Pages[0].Lastmod
 		}
 
 		rssLayouts := []string{"rss.xml", "_default/rss.xml", "_internal/_default/rss.xml"}
@@ -1317,6 +1323,7 @@ func (s *Site) RenderSitemap() error {
 
 	page := &Page{}
 	page.Date = s.Info.LastChange
+	page.Lastmod = s.Info.LastChange
 	page.Site = &s.Info
 	page.URL = "/"