hugolib: Support sub-sections in permalink settings

This enables both the variants below:

Current (first level only):

```
"blog": ":section/:title",
```

Nested (all levels):

```
"blog": ":sections/:title",
```

Should ideally been part of Hugo 0.22, but better late than never ...

Fixes #3580

hugolib/permalinks.go

@@ -16,6 +16,7 @@ package hugolib
 import (
 	"errors"
 	"fmt"
+	"path"
 	"regexp"
 	"strconv"
 	"strings"
@@ -182,6 +183,12 @@ func pageToPermalinkSection(p *Page, _ string) (string, error) {
 	return p.Section(), nil
 }
 
+func pageToPermalinkSections(p *Page, _ string) (string, error) {
+	// TODO(bep) we have some superflous URLize in this file, but let's
+	// deal with that later.
+	return path.Join(p.current().sections...), nil
+}
+
 func init() {
 	knownPermalinkAttributes = map[string]pageToPermaAttribute{
 		"year":        pageToPermalinkDate,
@@ -192,6 +199,7 @@ func init() {
 		"weekdayname": pageToPermalinkDate,
 		"yearday":     pageToPermalinkDate,
 		"section":     pageToPermalinkSection,
+		"sections":    pageToPermalinkSections,
 		"title":       pageToPermalinkTitle,
 		"slug":        pageToPermalinkSlugElseTitle,
 		"filename":    pageToPermalinkFilename,

hugolib/site_sections_test.go

@@ -32,6 +32,10 @@ func TestNestedSections(t *testing.T) {
 		th      = testHelper{cfg, fs, t}
 	)
 
+	cfg.Set("permalinks", map[string]string{
+		"perm a": ":sections/:title",
+	})
+
 	pageTemplate := `---
 title: T%d_%d
 ---
@@ -64,6 +68,15 @@ Content
 	writeSource(t, fs, filepath.Join("content", "empty3", "b", "c", "d", "_index.md"), fmt.Sprintf(pageTemplate, 41, -1))
 	writeSource(t, fs, filepath.Join("content", "empty3", "b", "empty3.md"), fmt.Sprintf(pageTemplate, 3, -1))
 
+	// Section with permalink config
+	writeSource(t, fs, filepath.Join("content", "perm a", "link", "_index.md"), fmt.Sprintf(pageTemplate, 9, -1))
+	for i := 1; i < 4; i++ {
+		writeSource(t, fs, filepath.Join("content", "perm a", "link", fmt.Sprintf("page_%d.md", i)),
+			fmt.Sprintf(pageTemplate, 1, i))
+	}
+	writeSource(t, fs, filepath.Join("content", "perm a", "link", "regular", fmt.Sprintf("page_%d.md", 5)),
+		fmt.Sprintf(pageTemplate, 1, 5))
+
 	writeSource(t, fs, filepath.Join("content", "l1", "l2", "_index.md"), fmt.Sprintf(pageTemplate, 2, -1))
 	writeSource(t, fs, filepath.Join("content", "l1", "l2_2", "_index.md"), fmt.Sprintf(pageTemplate, 22, -1))
 	writeSource(t, fs, filepath.Join("content", "l1", "l2", "l3", "_index.md"), fmt.Sprintf(pageTemplate, 3, -1))
@@ -96,7 +109,7 @@ PAG|{{ .Title }}|{{ $sect.InSection . }}
 	cfg.Set("paginate", 2)
 
 	s := buildSingleSite(t, deps.DepsCfg{Fs: fs, Cfg: cfg}, BuildCfg{})
-	require.Len(t, s.RegularPages, 14)
+	require.Len(t, s.RegularPages, 18)
 
 	tests := []struct {
 		sections string
@@ -185,6 +198,18 @@ PAG|{{ .Title }}|{{ $sect.InSection . }}
 			assert.Equal("T2_-1", p.Parent().Title)
 			assert.Len(p.Sections(), 0)
 		}},
+		{"perm a,link", func(p *Page) {
+			assert.Equal("T9_-1", p.Title)
+			assert.Equal("/perm-a/link/", p.RelPermalink())
+			assert.Len(p.Pages, 4)
+			first := p.Pages[0]
+			assert.Equal("/perm-a/link/t1_1/", first.RelPermalink())
+			th.assertFileContent("public/perm-a/link/t1_1/index.html", "Single|T1_1")
+
+			last := p.Pages[3]
+			assert.Equal("/perm-a/link/t1_5/", last.RelPermalink())
+
+		}},
 	}
 
 	for _, test := range tests {
@@ -203,7 +228,7 @@ PAG|{{ .Title }}|{{ $sect.InSection . }}
 
 	assert.NotNil(home)
 
-	assert.Len(home.Sections(), 6)
+	assert.Len(home.Sections(), 7)
 
 	rootPage := s.getPage(KindPage, "mypage.md")
 	assert.NotNil(rootPage)