Make string sorting (e.g. ByTitle, ByLinkTitle and ByParam) language aware

Fixes #2180

3 files changed, 133 insertions, 13 deletions

diff --git a/resources/page/integration_test.go b/resources/page/integration_test.go
index 285b14342..9dc322b4a 100644
--- a/resources/page/integration_test.go
+++ b/resources/page/integration_test.go
@@ -70,3 +70,69 @@ date: "2020-02-01"
 	b.AssertFileContent("public/en/index.html", "0|February, 2020|Pages(1)1|January, 2020|Pages(1)")
 	b.AssertFileContent("public/fr/index.html", "0|février, 2020|Pages(1)1|janvier, 2020|Pages(1)")
 }
+
+func TestPagesSortCollation(t *testing.T) {
+
+	files := `
+-- config.toml --
+defaultContentLanguage = 'en'
+defaultContentLanguageInSubdir = true
+[languages]
+[languages.en]
+title = 'My blog'
+weight = 1
+[languages.fr]
+title = 'Mon blogue'
+weight = 2
+[languages.nn]
+title = 'Bloggen min'
+weight = 3
+-- content/p1.md --
+---
+title: "zulu"
+date: "2020-01-01"
+param1: "xylophone"
+tags: ["xylophone", "éclair", "zulu", "emma"]
+---
+-- content/p2.md --
+---
+title: "émotion"
+date: "2020-01-01"
+param1: "violin"
+---
+-- content/p3.md --
+---
+title: "alpha"
+date: "2020-01-01"
+param1: "éclair"
+---
+-- layouts/index.html --
+ByTitle: {{ range site.RegularPages.ByTitle }}{{ .Title }}|{{ end }}
+ByLinkTitle: {{ range site.RegularPages.ByLinkTitle }}{{ .Title }}|{{ end }}
+ByParam: {{ range site.RegularPages.ByParam "param1" }}{{ .Params.param1 }}|{{ end }}
+Tags Alphabetical: {{  range site.Taxonomies.tags.Alphabetical }}{{ .Term }}|{{ end }}
+GroupBy: {{ range site.RegularPages.GroupBy "Title" }}{{ .Key }}|{{ end }}
+{{ with (site.GetPage "p1").Params.tags }}
+Sort: {{  sort . }}
+ByWeight: {{ range site.RegularPages.ByWeight }}{{ .Title }}|{{ end }}
+{{ end }}
+
+	`
+
+	b := hugolib.NewIntegrationTestBuilder(
+		hugolib.IntegrationTestConfig{
+			T:           t,
+			TxtarString: files,
+			NeedsOsFS:   true,
+		}).Build()
+
+	b.AssertFileContent("public/en/index.html", `
+ByTitle: alpha|émotion|zulu|
+ByLinkTitle: alpha|émotion|zulu|
+ByParam: éclair|violin|xylophone
+Tags Alphabetical: éclair|emma|xylophone|zulu|
+GroupBy: alpha|émotion|zulu|
+Sort: [éclair emma xylophone zulu]
+ByWeight: alpha|émotion|zulu|
+`)
+}
diff --git a/resources/page/pagegroup.go b/resources/page/pagegroup.go
index 601af606a..1d9827907 100644
--- a/resources/page/pagegroup.go
+++ b/resources/page/pagegroup.go
@@ -53,13 +53,16 @@ type mapKeyByInt struct{ mapKeyValues }
 
 func (s mapKeyByInt) Less(i, j int) bool { return s.mapKeyValues[i].Int() < s.mapKeyValues[j].Int() }
 
-type mapKeyByStr struct{ mapKeyValues }
+type mapKeyByStr struct {
+	less func(a, b string) bool
+	mapKeyValues
+}
 
 func (s mapKeyByStr) Less(i, j int) bool {
-	return compare.LessStrings(s.mapKeyValues[i].String(), s.mapKeyValues[j].String())
+	return s.less(s.mapKeyValues[i].String(), s.mapKeyValues[j].String())
 }
 
-func sortKeys(v []reflect.Value, order string) []reflect.Value {
+func sortKeys(examplePage Page, v []reflect.Value, order string) []reflect.Value {
 	if len(v) <= 1 {
 		return v
 	}
@@ -72,10 +75,12 @@ func sortKeys(v []reflect.Value, order string) []reflect.Value {
 			sort.Sort(mapKeyByInt{v})
 		}
 	case reflect.String:
+		stringLess, close := collatorStringLess(examplePage)
+		defer close()
 		if order == "desc" {
-			sort.Sort(sort.Reverse(mapKeyByStr{v}))
+			sort.Sort(sort.Reverse(mapKeyByStr{stringLess, v}))
 		} else {
-			sort.Sort(mapKeyByStr{v})
+			sort.Sort(mapKeyByStr{stringLess, v})
 		}
 	}
 	return v
@@ -161,7 +166,7 @@ func (p Pages) GroupBy(key string, order ...string) (PagesGroup, error) {
 		tmp.SetMapIndex(fv, reflect.Append(tmp.MapIndex(fv), ppv))
 	}
 
-	sortedKeys := sortKeys(tmp.MapKeys(), direction)
+	sortedKeys := sortKeys(p[0], tmp.MapKeys(), direction)
 	r := make([]PageGroup, len(sortedKeys))
 	for i, k := range sortedKeys {
 		r[i] = PageGroup{Key: k.Interface(), Pages: tmp.MapIndex(k).Interface().(Pages)}
@@ -213,7 +218,7 @@ func (p Pages) GroupByParam(key string, order ...string) (PagesGroup, error) {
 	}
 
 	var r []PageGroup
-	for _, k := range sortKeys(tmp.MapKeys(), direction) {
+	for _, k := range sortKeys(p[0], tmp.MapKeys(), direction) {
 		r = append(r, PageGroup{Key: k.Interface(), Pages: tmp.MapIndex(k).Interface().(Pages)})
 	}
 
diff --git a/resources/page/pages_sort.go b/resources/page/pages_sort.go
index 02096dadd..08cb34a32 100644
--- a/resources/page/pages_sort.go
+++ b/resources/page/pages_sort.go
@@ -17,6 +17,7 @@ import (
 	"sort"
 
 	"github.com/gohugoio/hugo/common/collections"
+	"github.com/gohugoio/hugo/langs"
 
 	"github.com/gohugoio/hugo/resources/resource"
 
@@ -72,7 +73,7 @@ var (
 		}
 		if p1.Weight() == p2.Weight() {
 			if p1.Date().Unix() == p2.Date().Unix() {
-				c := compare.Strings(p1.LinkTitle(), p2.LinkTitle())
+				c := collatorStringCompare(func(p Page) string { return p.LinkTitle() }, p1, p2)
 				if c == 0 {
 					if p1.File().IsZero() || p2.File().IsZero() {
 						return p1.File().IsZero()
@@ -121,11 +122,11 @@ var (
 	}
 
 	lessPageTitle = func(p1, p2 Page) bool {
-		return compare.LessStrings(p1.Title(), p2.Title())
+		return collatorStringCompare(func(p Page) string { return p.Title() }, p1, p2) < 0
 	}
 
 	lessPageLinkTitle = func(p1, p2 Page) bool {
-		return compare.LessStrings(p1.LinkTitle(), p2.LinkTitle())
+		return collatorStringCompare(func(p Page) string { return p.LinkTitle() }, p1, p2) < 0
 	}
 
 	lessPageDate = func(p1, p2 Page) bool {
@@ -151,6 +152,46 @@ func (p Pages) Limit(n int) Pages {
 	return p
 }
 
+var collatorStringSort = func(getString func(Page) string) func(p Pages) {
+	return func(p Pages) {
+		if len(p) == 0 {
+			return
+		}
+		// Pages may be a mix of multiple languages, so we need to use the language
+		// for the currently rendered Site.
+		currentSite := p[0].Site().Current()
+		coll := langs.GetCollator(currentSite.Language())
+		coll.Lock()
+		defer coll.Unlock()
+
+		sort.SliceStable(p, func(i, j int) bool {
+			return coll.CompareStrings(getString(p[i]), getString(p[j])) < 0
+		})
+	}
+}
+
+var collatorStringCompare = func(getString func(Page) string, p1, p2 Page) int {
+	currentSite := p1.Site().Current()
+	coll := langs.GetCollator(currentSite.Language())
+	coll.Lock()
+	c := coll.CompareStrings(getString(p1), getString(p2))
+	coll.Unlock()
+	return c
+}
+
+var collatorStringLess = func(p Page) (less func(s1, s2 string) bool, close func()) {
+	currentSite := p.Site().Current()
+	coll := langs.GetCollator(currentSite.Language())
+	coll.Lock()
+	return func(s1, s2 string) bool {
+			return coll.CompareStrings(s1, s2) < 1
+		},
+		func() {
+			coll.Unlock()
+		}
+
+}
+
 // ByWeight sorts the Pages by weight and returns a copy.
 //
 // Adjacent invocations on the same receiver will return a cached result.
@@ -175,7 +216,8 @@ func SortByDefault(pages Pages) {
 func (p Pages) ByTitle() Pages {
 	const key = "pageSort.ByTitle"
 
-	pages, _ := spc.get(key, pageBy(lessPageTitle).Sort, p)
+	pages, _ := spc.get(key, collatorStringSort(func(p Page) string { return p.Title() }), p)
+
 	return pages
 }
 
@@ -187,7 +229,7 @@ func (p Pages) ByTitle() Pages {
 func (p Pages) ByLinkTitle() Pages {
 	const key = "pageSort.ByLinkTitle"
 
-	pages, _ := spc.get(key, pageBy(lessPageLinkTitle).Sort, p)
+	pages, _ := spc.get(key, collatorStringSort(func(p Page) string { return p.LinkTitle() }), p)
 
 	return pages
 }
@@ -323,9 +365,15 @@ func (p Pages) Reverse() Pages {
 //
 // This may safely be executed  in parallel.
 func (p Pages) ByParam(paramsKey any) Pages {
+	if len(p) < 2 {
+		return p
+	}
 	paramsKeyStr := cast.ToString(paramsKey)
 	key := "pageSort.ByParam." + paramsKeyStr
 
+	stringLess, close := collatorStringLess(p[0])
+	defer close()
+
 	paramsKeyComparator := func(p1, p2 Page) bool {
 		v1, _ := p1.Param(paramsKeyStr)
 		v2, _ := p2.Param(paramsKeyStr)
@@ -354,7 +402,8 @@ func (p Pages) ByParam(paramsKey any) Pages {
 		s1 := cast.ToString(v1)
 		s2 := cast.ToString(v2)
 
-		return compare.LessStrings(s1, s2)
+		return stringLess(s1, s2)
+
 	}
 
 	pages, _ := spc.get(key, pageBy(paramsKeyComparator).Sort, p)