page: Add IndexOf method to Pages

See #13589

resources/page/pages.go

@@ -130,6 +130,11 @@ func (pages Pages) ProbablyEq(other any) bool {
 	return true
 }
 
+// IndexOf returns the index of page in p, or -1 if not found.
+func (p Pages) IndexOf(page Page) int {
+	return searchPage(page, p)
+}
+
 // PagesFactory somehow creates some Pages.
 // We do a lot of lazy Pages initialization in Hugo, so we need a type.
 type PagesFactory func() Pages

resources/page/pages_test.go

@@ -70,3 +70,15 @@ func TestToPages(t *testing.T) {
 	_, err := ToPages("not a page")
 	c.Assert(err, qt.Not(qt.IsNil))
 }
+
+func TestIndexOf(t *testing.T) {
+	c := qt.New(t)
+
+	p1, p2, p3, p4 := &testPage{title: "p1"}, &testPage{title: "p2"}, &testPage{title: "p3"}, &testPage{title: "p4"}
+
+	pages := Pages{p1, p2, p3}
+	c.Assert(pages.IndexOf(p1), qt.Equals, 0)
+	c.Assert(pages.IndexOf(p2), qt.Equals, 1)
+	c.Assert(pages.IndexOf(p3), qt.Equals, 2)
+	c.Assert(pages.IndexOf(p4), qt.Equals, -1)
+}