markup: Add Level to Heading struct

Closes #10776

markup/goldmark/toc.go

@@ -80,6 +80,7 @@ func (t *tocTransformer) Transform(n *ast.Document, reader text.Reader, pc parse
 			id, found := heading.AttributeString("id")
 			if found {
 				tocHeading.ID = string(id.([]byte))
+				tocHeading.Level = level
 			}
 		case
 			ast.KindCodeSpan,

markup/tableofcontents/integration_test.go

@@ -0,0 +1,45 @@
+// Copyright 2023 The Hugo Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package tableofcontents_test
+
+import (
+	"testing"
+
+	"github.com/gohugoio/hugo/hugolib"
+)
+
+// Issue #10776
+func TestHeadingsLevel(t *testing.T) {
+	t.Parallel()
+
+	files := `
+-- hugo.toml --
+disableKinds = ['page','rss','section','sitemap','taxonomy','term']
+-- layouts/index.html --
+{{ range .Fragments.HeadingsMap }}
+	{{ printf "%s|%d|%s" .ID .Level .Title }}
+{{ end }}
+-- content/_index.md --
+## Heading L2
+### Heading L3
+##### Heading L5
+`
+
+	b := hugolib.Test(t, files)
+	b.AssertFileContent("public/index.html",
+		"heading-l2|2|Heading L2",
+		"heading-l3|3|Heading L3",
+		"heading-l5|5|Heading L5",
+	)
+}

markup/tableofcontents/tableofcontents.go

@@ -77,6 +77,7 @@ func (h Headings) FilterBy(fn func(*Heading) bool) Headings {
 // Heading holds the data about a heading and its children.
 type Heading struct {
 	ID    string
+	Level int
 	Title string
 
 	Headings Headings