resources/page: Expand parmalinks tokens in `url`

This change allows to use permalink tokens in url front matter fields. This should be useful to target more specific pages instead of using a global permalink configuration. It's expected to be used with cascade.

Fixes #9714

2 files changed, 72 insertions, 11 deletions

diff --git a/resources/page/permalinks.go b/resources/page/permalinks.go
index 67c63c4b2..05911f0ea 100644
--- a/resources/page/permalinks.go
+++ b/resources/page/permalinks.go
@@ -40,6 +40,8 @@ type PermalinkExpander struct {
 	expanders map[string]map[string]func(Page) (string, error)
 
 	urlize func(uri string) string
+
+	patternCache *maps.Cache[string, func(Page) (string, error)]
 }
 
 // Time for checking date formats. Every field is different than the
@@ -71,7 +73,10 @@ func (p PermalinkExpander) callback(attr string) (pageToPermaAttribute, bool) {
 // NewPermalinkExpander creates a new PermalinkExpander configured by the given
 // urlize func.
 func NewPermalinkExpander(urlize func(uri string) string, patterns map[string]map[string]string) (PermalinkExpander, error) {
-	p := PermalinkExpander{urlize: urlize}
+	p := PermalinkExpander{
+		urlize:       urlize,
+		patternCache: maps.NewCache[string, func(Page) (string, error)](),
+	}
 
 	p.knownPermalinkAttributes = map[string]pageToPermaAttribute{
 		"year":           p.pageToPermalinkDate,
@@ -102,6 +107,16 @@ func NewPermalinkExpander(urlize func(uri string) string, patterns map[string]ma
 	return p, nil
 }
 
+// ExpandPattern expands the path in p with the specified expand pattern.
+func (l PermalinkExpander) ExpandPattern(pattern string, p Page) (string, error) {
+	expander, err := l.getOrParsePattern(pattern)
+	if err != nil {
+		return "", err
+	}
+
+	return expander(p)
+}
+
 // Expand expands the path in p according to the rules defined for the given key.
 // If no rules are found for the given key, an empty string is returned.
 func (l PermalinkExpander) Expand(key string, p Page) (string, error) {
@@ -129,17 +144,11 @@ func init() {
 	}
 }
 
-func (l PermalinkExpander) parse(patterns map[string]string) (map[string]func(Page) (string, error), error) {
-	expanders := make(map[string]func(Page) (string, error))
-
-	for k, pattern := range patterns {
-		k = strings.Trim(k, sectionCutSet)
-
+func (l PermalinkExpander) getOrParsePattern(pattern string) (func(Page) (string, error), error) {
+	return l.patternCache.GetOrCreate(pattern, func() (func(Page) (string, error), error) {
 		if !l.validate(pattern) {
 			return nil, &permalinkExpandError{pattern: pattern, err: errPermalinkIllFormed}
 		}
-
-		pattern := pattern
 		matches := attributeRegexp.FindAllStringSubmatch(pattern, -1)
 
 		callbacks := make([]pageToPermaAttribute, len(matches))
@@ -157,7 +166,7 @@ func (l PermalinkExpander) parse(patterns map[string]string) (map[string]func(Pa
 			callbacks[i] = callback
 		}
 
-		expanders[k] = func(p Page) (string, error) {
+		return func(p Page) (string, error) {
 			if matches == nil {
 				return pattern, nil
 			}
@@ -173,12 +182,25 @@ func (l PermalinkExpander) parse(patterns map[string]string) (map[string]func(Pa
 				}
 
 				newField = strings.Replace(newField, replacement, newAttr, 1)
-
 			}
 
 			return newField, nil
+		}, nil
+	})
+}
+
+func (l PermalinkExpander) parse(patterns map[string]string) (map[string]func(Page) (string, error), error) {
+	expanders := make(map[string]func(Page) (string, error))
+
+	for k, pattern := range patterns {
+		k = strings.Trim(k, sectionCutSet)
+
+		expander, err := l.getOrParsePattern(pattern)
+		if err != nil {
+			return nil, err
 		}
 
+		expanders[k] = expander
 	}
 
 	return expanders, nil
diff --git a/resources/page/permalinks_integration_test.go b/resources/page/permalinks_integration_test.go
index 9a76ac602..2b9e878b1 100644
--- a/resources/page/permalinks_integration_test.go
+++ b/resources/page/permalinks_integration_test.go
@@ -193,3 +193,42 @@ List.
 	b.AssertFileContent("public/libros/fiction/index.html", "List.")
 	b.AssertFileContent("public/libros/fiction/2023/book1/index.html", "Single.")
 }
+
+func TestPermalinksUrlCascade(t *testing.T) {
+	t.Parallel()
+
+	files := `
+-- layouts/_default/list.html --
+List|{{ .Kind }}|{{ .RelPermalink }}|
+-- layouts/_default/single.html --
+Single|{{ .Kind }}|{{ .RelPermalink }}|
+-- hugo.toml --
+-- content/cooking/delicious-recipes/_index.md --
+---
+url: /delicious-recipe/
+cascade:
+  url: /delicious-recipe/:slug/
+---
+-- content/cooking/delicious-recipes/example1.md --
+---
+title: Recipe 1
+---
+-- content/cooking/delicious-recipes/example2.md --
+---
+title: Recipe 2
+slug: custom-recipe-2
+---
+`
+	b := hugolib.NewIntegrationTestBuilder(
+		hugolib.IntegrationTestConfig{
+			T:           t,
+			TxtarString: files,
+			LogLevel:    logg.LevelWarn,
+		}).Build()
+
+	t.Log(b.LogString())
+	b.Assert(b.H.Log.LoggCount(logg.LevelWarn), qt.Equals, 0)
+	b.AssertFileContent("public/delicious-recipe/index.html", "List|section|/delicious-recipe/")
+	b.AssertFileContent("public/delicious-recipe/recipe-1/index.html", "Single|page|/delicious-recipe/recipe-1/")
+	b.AssertFileContent("public/delicious-recipe/custom-recipe-2/index.html", "Single|page|/delicious-recipe/custom-recipe-2/")
+}