tpl: Fix some baseof lookup issues

We were mistakingly using the templates (e.g. list.html) descriptor to resolve the base template and not the page,
which worked fine in most cases, but not all.

Fixes #13583

2 files changed, 33 insertions, 5 deletions

diff --git a/tpl/templates/templates_integration_test.go b/tpl/templates/templates_integration_test.go
index a0dcf0348..752709593 100644
--- a/tpl/templates/templates_integration_test.go
+++ b/tpl/templates/templates_integration_test.go
@@ -166,3 +166,31 @@ p3.current.Ancestors.Reverse: {{ with templates.Current }}{{ range .Ancestors.Re
 		"p2.current.Ancestors: _partials/p1.html|all.html",
 	)
 }
+
+func TestBaseOfIssue13583(t *testing.T) {
+	t.Parallel()
+
+	files := `
+-- hugo.toml --
+-- content/_index.md --
+---
+title: "Home"
+outputs: ["html", "amp"]
+---
+title: "Home"
+-- layouts/baseof.html --
+layouts/baseof.html
+{{ block "main" . }}{{ end }}
+-- layouts/baseof.amp.html --
+layouts/baseof.amp.html
+{{ block "main" . }}{{ end }}
+-- layouts/home.html --
+{{ define "main" }}
+Home.
+{{ end }}
+
+`
+	b := hugolib.Test(t, files)
+	b.AssertFileContent("public/index.html", "layouts/baseof.html")
+	b.AssertFileContent("public/amp/index.html", "layouts/baseof.amp.html")
+}
diff --git a/tpl/tplimpl/templatestore.go b/tpl/tplimpl/templatestore.go
index eee962053..3c8c4abf2 100644
--- a/tpl/tplimpl/templatestore.go
+++ b/tpl/tplimpl/templatestore.go
@@ -301,7 +301,7 @@ func (ti *TemplInfo) String() string {
 	return ti.PathInfo.String()
 }
 
-func (ti *TemplInfo) findBestMatchBaseof(s *TemplateStore, k1 string, slashCountK1 int, best *bestMatch) {
+func (ti *TemplInfo) findBestMatchBaseof(s *TemplateStore, d1 TemplateDescriptor, k1 string, slashCountK1 int, best *bestMatch) {
 	if ti.baseVariants == nil {
 		return
 	}
@@ -310,11 +310,11 @@ func (ti *TemplInfo) findBestMatchBaseof(s *TemplateStore, k1 string, slashCount
 		slashCountK2 := strings.Count(k2, "/")
 		distance := slashCountK1 - slashCountK2
 
-		for d, vv := range v {
-			weight := s.dh.compareDescriptors(CategoryBaseof, ti.D, d)
+		for d2, vv := range v {
+			weight := s.dh.compareDescriptors(CategoryBaseof, d1, d2)
 			weight.distance = distance
 			if best.isBetter(weight, vv.Template) {
-				best.updateValues(weight, k2, d, vv.Template)
+				best.updateValues(weight, k2, d2, vv.Template)
 			}
 		}
 		return false, nil
@@ -538,7 +538,7 @@ func (s *TemplateStore) LookupPagesLayout(q TemplateQuery) *TemplInfo {
 		return m
 	}
 	best1.reset()
-	m.findBestMatchBaseof(s, key, slashCountKey, best1)
+	m.findBestMatchBaseof(s, q.Desc, key, slashCountKey, best1)
 	if best1.w.w1 <= 0 {
 		return nil
 	}