content adapter: Fix site.GetPage using the base part of the path

Fixes #12561

hugolib/content_map_page.go

@@ -932,8 +932,8 @@ func newPageMap(i int, s *Site, mcache *dynacache.Cache, pageTrees *pageTrees) *
 				LockType: doctree.LockTypeRead,
 				Handle: func(s string, n contentNodeI, match doctree.DimensionFlag) (bool, error) {
 					p := n.(*pageState)
-					if p.File() != nil {
-						add(p.File().FileInfo().Meta().PathInfo.BaseNameNoIdentifier(), p)
+					if p.PathInfo() != nil {
+						add(p.PathInfo().BaseNameNoIdentifier(), p)
 					}
 					return false, nil
 				},

hugolib/pagecollections_test.go

@@ -693,3 +693,36 @@ draft: true
 	b.AssertFileContent("public/s1-foo/index.html", "/s1-foo/: Pages: /s1-foo/p2/|/s1-foo/s2-foo/|/s1-foo/s2/|$")
 	b.AssertFileContent("public/s1-foo/s2/index.html", "/s1-foo/s2/: Pages: /s1-foo/s2/p3/|$")
 }
+
+func TestGetPageContentAdapterBaseIssue12561(t *testing.T) {
+	t.Parallel()
+
+	files := `
+-- hugo.toml --
+disableKinds = ['rss','section','sitemap','taxonomy','term']
+-- layouts/index.html --
+Test A: {{ (site.GetPage "/s1/p1").Title }}
+Test B: {{ (site.GetPage "p1").Title }}
+Test C: {{ (site.GetPage "/s2/p2").Title }}
+Test D: {{ (site.GetPage "p2").Title }}
+-- layouts/_default/single.html --
+{{ .Title }}
+-- content/s1/p1.md --
+---
+title: p1
+---
+-- content/s2/_content.gotmpl --
+{{ .AddPage (dict "path" "p2" "title" "p2") }}
+`
+
+	b := Test(t, files)
+
+	b.AssertFileExists("public/s1/p1/index.html", true)
+	b.AssertFileExists("public/s2/p2/index.html", true)
+	b.AssertFileContent("public/index.html",
+		"Test A: p1",
+		"Test B: p1",
+		"Test C: p2",
+		"Test D: p2", // fails
+	)
+}