hugolib: Fix .Site.LastChange

This commit makes sure that the `.Site.LastChange` is fetched from the latest page modification date.

Previously, this value was fetched from the last page in the default page sort, which may not be the last by date
if weight is set.

Fixes #2909
Closes #2910

3 files changed, 32 insertions, 4 deletions

diff --git a/hugolib/hugo_sites_build.go b/hugolib/hugo_sites_build.go
index 059b0fe1e..2715e8977 100644
--- a/hugolib/hugo_sites_build.go
+++ b/hugolib/hugo_sites_build.go
@@ -168,7 +168,7 @@ func (h *HugoSites) assemble(config *BuildCfg) error {
 
 	for _, s := range h.Sites {
 		s.refreshPageCaches()
-		s.setupPrevNext()
+		s.setupSitePages()
 	}
 
 	if err := h.assignMissingTranslations(); err != nil {
diff --git a/hugolib/site.go b/hugolib/site.go
index 31a8606f9..a9a150f7e 100644
--- a/hugolib/site.go
+++ b/hugolib/site.go
@@ -821,7 +821,9 @@ func (s *Site) process(config BuildCfg) (err error) {
 
 }
 
-func (s *Site) setupPrevNext() {
+func (s *Site) setupSitePages() {
+	var siteLastChange time.Time
+
 	for i, page := range s.Pages {
 		if i < len(s.Pages)-1 {
 			page.Next = s.Pages[i+1]
@@ -830,7 +832,18 @@ func (s *Site) setupPrevNext() {
 		if i > 0 {
 			page.Prev = s.Pages[i-1]
 		}
+
+		// Determine Site.Info.LastChange
+		// Note that the logic to determine which date to use for Lastmod
+		// is already applied, so this is *the* date to use.
+		// We cannot just pick the last page in the default sort, because
+		// that may not be ordered by date.
+		if page.Lastmod.After(siteLastChange) {
+			siteLastChange = page.Lastmod
+		}
 	}
+
+	s.Info.LastChange = siteLastChange
 }
 
 func (s *Site) render() (err error) {
@@ -1371,8 +1384,6 @@ func (s *Site) buildSiteMeta() (err error) {
 
 	s.assembleMenus()
 
-	s.Info.LastChange = s.Pages[0].Lastmod
-
 	return
 }
 
diff --git a/hugolib/site_test.go b/hugolib/site_test.go
index 9629f763a..7919ba377 100644
--- a/hugolib/site_test.go
+++ b/hugolib/site_test.go
@@ -184,6 +184,23 @@ func TestFutureExpirationRender(t *testing.T) {
 	}
 }
 
+func TestLastChange(t *testing.T) {
+	t.Parallel()
+
+	cfg, fs := newTestCfg()
+
+	writeSource(t, fs, filepath.Join("content", "sect/doc1.md"), "---\ntitle: doc1\nweight: 1\ndate: 2014-05-29\n---\n# doc1\n*some content*")
+	writeSource(t, fs, filepath.Join("content", "sect/doc2.md"), "---\ntitle: doc2\nweight: 2\ndate: 2015-05-29\n---\n# doc2\n*some content*")
+	writeSource(t, fs, filepath.Join("content", "sect/doc3.md"), "---\ntitle: doc3\nweight: 3\ndate: 2017-05-29\n---\n# doc3\n*some content*")
+	writeSource(t, fs, filepath.Join("content", "sect/doc4.md"), "---\ntitle: doc4\nweight: 4\ndate: 2016-05-29\n---\n# doc4\n*some content*")
+	writeSource(t, fs, filepath.Join("content", "sect/doc5.md"), "---\ntitle: doc5\nweight: 3\n---\n# doc5\n*some content*")
+
+	s := buildSingleSite(t, deps.DepsCfg{Fs: fs, Cfg: cfg}, BuildCfg{SkipRender: true})
+
+	require.False(t, s.Info.LastChange.IsZero(), "Site.LastChange is zero")
+	require.Equal(t, 2017, s.Info.LastChange.Year(), "Site.LastChange should be set to the page with latest Lastmod (year 2017)")
+}
+
 // Issue #957
 func TestCrossrefs(t *testing.T) {
 	t.Parallel()