hugolib: Fix section logic for root folders with subfolders

This commit fixes an issue introduced in the recently released Hugo 0.22.

This logic did not handle the case with root sections with non-section subfolders very well.

Fixes #3586

hugolib/site_sections_test.go

@@ -58,6 +58,11 @@ Content
 			fmt.Sprintf(pageTemplate, 1, level1))
 	}
 
+	// Issue #3586
+	writeSource(t, fs, filepath.Join("content", "post", "0000.md"), fmt.Sprintf(pageTemplate, 1, 2))
+	writeSource(t, fs, filepath.Join("content", "post", "0000", "0001.md"), fmt.Sprintf(pageTemplate, 1, 3))
+	writeSource(t, fs, filepath.Join("content", "elsewhere", "0003.md"), fmt.Sprintf(pageTemplate, 1, 4))
+
 	// Empty nested section, i.e. no regular content pages.
 	writeSource(t, fs, filepath.Join("content", "empty1", "b", "c", "_index.md"), fmt.Sprintf(pageTemplate, 33, -1))
 	// Index content file a the end and in the middle.
@@ -109,12 +114,24 @@ PAG|{{ .Title }}|{{ $sect.InSection . }}
 	cfg.Set("paginate", 2)
 
 	s := buildSingleSite(t, deps.DepsCfg{Fs: fs, Cfg: cfg}, BuildCfg{})
-	require.Len(t, s.RegularPages, 18)
+	require.Len(t, s.RegularPages, 21)
 
 	tests := []struct {
 		sections string
 		verify   func(p *Page)
 	}{
+		{"elsewhere", func(p *Page) {
+			assert.Len(p.Pages, 1)
+			for _, p := range p.Pages {
+				assert.Equal([]string{"elsewhere"}, p.sections)
+			}
+		}},
+		{"post", func(p *Page) {
+			assert.Len(p.Pages, 2)
+			for _, p := range p.Pages {
+				assert.Equal("post", p.Section())
+			}
+		}},
 		{"empty1", func(p *Page) {
 			// > b,c
 			assert.NotNil(p.s.getPage(KindSection, "empty1", "b"))
@@ -228,7 +245,7 @@ PAG|{{ .Title }}|{{ $sect.InSection . }}
 
 	assert.NotNil(home)
 
-	assert.Len(home.Sections(), 7)
+	assert.Len(home.Sections(), 9)
 
 	rootPage := s.getPage(KindPage, "mypage.md")
 	assert.NotNil(rootPage)