tpl/urls: Add JoinPath template function

See https://pkg.go.dev/net/url#JoinPath

Closes #9694

4 files changed, 102 insertions, 0 deletions

diff --git a/docs/content/en/functions/urls.JoinPath.md b/docs/content/en/functions/urls.JoinPath.md
new file mode 100644
index 000000000..c0e0464b6
--- /dev/null
+++ b/docs/content/en/functions/urls.JoinPath.md
@@ -0,0 +1,24 @@
+---
+title: urls.JoinPath
+description: Joins the provided elements into a URL string and cleans the result of any ./ or ../ elements.
+categories: [functions]
+menu:
+  docs:
+    parent: functions
+keywords: [urls,path,join]
+signature: ["urls.JoinPath ELEMENT..."]
+---
+
+```go-html-template
+{{ urls.JoinPath "" }} → "/"
+{{ urls.JoinPath "a" }} → "a"
+{{ urls.JoinPath "a" "b" }} → "a/b"
+{{ urls.JoinPath "/a" "b" }} → "/a/b"
+{{ urls.JoinPath "https://example.org" "b" }} → "https://example.org/b"
+
+{{ urls.JoinPath (slice "a" "b") }} → "a/b"
+```
+
+Unlike the [`path.Join`] function, `urls.JoinPath` retains consecutive leading slashes.
+
+[`path.Join`]: /functions/path.join/
diff --git a/tpl/urls/init.go b/tpl/urls/init.go
index ec954640d..cdc597f34 100644
--- a/tpl/urls/init.go
+++ b/tpl/urls/init.go
@@ -68,6 +68,14 @@ func init() {
 			},
 		)
 
+		ns.AddMethodMapping(ctx.JoinPath,
+			nil,
+			[][2]string{
+				{`{{ urls.JoinPath "https://example.org" "foo" }}`, `https://example.org/foo`},
+				{`{{ urls.JoinPath (slice "a" "b") }}`, `a/b`},
+			},
+		)
+
 		return ns
 	}
 
diff --git a/tpl/urls/urls.go b/tpl/urls/urls.go
index 551b53875..5de2342d4 100644
--- a/tpl/urls/urls.go
+++ b/tpl/urls/urls.go
@@ -185,3 +185,38 @@ func (ns *Namespace) AbsLangURL(s any) (template.HTML, error) {
 
 	return template.HTML(ns.deps.PathSpec.AbsURL(ss, !ns.multihost)), nil
 }
+
+// JoinPath joins the provided elements into a URL string and cleans the result
+// of any ./ or ../ elements.
+func (ns *Namespace) JoinPath(elements ...any) (string, error) {
+
+	var selements []string
+	for _, e := range elements {
+		switch v := e.(type) {
+		case []string:
+			for _, e := range v {
+				selements = append(selements, e)
+			}
+		case []any:
+			for _, e := range v {
+				se, err := cast.ToStringE(e)
+				if err != nil {
+					return "", err
+				}
+				selements = append(selements, se)
+			}
+		default:
+			se, err := cast.ToStringE(e)
+			if err != nil {
+				return "", err
+			}
+			selements = append(selements, se)
+		}
+	}
+
+	result, err := url.JoinPath(selements[0], selements[1:]...)
+	if err != nil {
+		return "", err
+	}
+	return result, nil
+}
diff --git a/tpl/urls/urls_test.go b/tpl/urls/urls_test.go
index f33e128be..1567875c0 100644
--- a/tpl/urls/urls_test.go
+++ b/tpl/urls/urls_test.go
@@ -69,3 +69,38 @@ func TestParse(t *testing.T) {
 			qt.CmpEquals(hqt.DeepAllowUnexported(&url.URL{}, url.Userinfo{})), test.expect)
 	}
 }
+
+func TestJoinPath(t *testing.T) {
+	t.Parallel()
+	c := qt.New(t)
+
+	for _, test := range []struct {
+		elements any
+		expect   any
+	}{
+		{"", `/`},
+		{"a", `a`},
+		{"/a/b", `/a/b`},
+		{"./../a/b", `a/b`},
+		{[]any{""}, `/`},
+		{[]any{"a"}, `a`},
+		{[]any{"/a", "b"}, `/a/b`},
+		{[]any{".", "..", "/a", "b"}, `a/b`},
+		{[]any{"https://example.org", "a"}, `https://example.org/a`},
+		{[]any{nil}, `/`},
+		// errors
+		{tstNoStringer{}, false},
+		{[]any{tstNoStringer{}}, false},
+	} {
+
+		result, err := ns.JoinPath(test.elements)
+
+		if b, ok := test.expect.(bool); ok && !b {
+			c.Assert(err, qt.Not(qt.IsNil))
+			continue
+		}
+
+		c.Assert(err, qt.IsNil)
+		c.Assert(result, qt.Equals, test.expect)
+	}
+}