Fix panic when passthrough elements are used in headings

Fixes #14677

Co-Authored-By: xingzihai <1315258019@qq.com>
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

markup/goldmark/convert.go

@@ -122,6 +122,12 @@ func newMarkdown(pcfg converter.ProviderConfig) goldmark.Markdown {
 		)
 	}
 
+	if cfg.Extensions.Passthrough.Enable {
+		tocRendererOptions = append(tocRendererOptions,
+			renderer.WithNodeRenderers(util.Prioritized(&tocPassthroughRenderer{}, 90)),
+		)
+	}
+
 	var (
 		extensions = []goldmark.Extender{
 			hugocontext.New(pcfg.Logger),

markup/goldmark/toc.go

@@ -24,6 +24,7 @@ import (
 	emojiAst "github.com/yuin/goldmark-emoji/ast"
 
 	"github.com/gohugoio/hugo-goldmark-extensions/extras"
+	"github.com/gohugoio/hugo-goldmark-extensions/passthrough"
 	"github.com/gohugoio/hugo/markup/tableofcontents"
 
 	"github.com/yuin/goldmark"
@@ -116,7 +117,9 @@ func (t *tocTransformer) Transform(n *ast.Document, reader text.Reader, pc parse
 			ast.KindAutoLink,
 			ast.KindRawHTML,
 			ast.KindText,
-			ast.KindString:
+			ast.KindString,
+			passthrough.KindPassthroughInline,
+			passthrough.KindPassthroughBlock:
 			err := t.r.Render(&headingText, reader.Source(), n)
 			if err != nil {
 				return s, err
@@ -171,6 +174,30 @@ func newTOCSanitizerPolicy() *bluemonday.Policy {
 	return p
 }
 
+// tocPassthroughRenderer renders passthrough nodes as raw text for the TOC.
+type tocPassthroughRenderer struct{}
+
+func (r *tocPassthroughRenderer) RegisterFuncs(reg renderer.NodeRendererFuncRegisterer) {
+	reg.Register(passthrough.KindPassthroughInline, r.render)
+	reg.Register(passthrough.KindPassthroughBlock, r.render)
+}
+
+func (r *tocPassthroughRenderer) render(w util.BufWriter, src []byte, node ast.Node, entering bool) (ast.WalkStatus, error) {
+	if !entering {
+		return ast.WalkContinue, nil
+	}
+	switch nn := node.(type) {
+	case *passthrough.PassthroughInline:
+		w.Write(nn.Segment.Value(src))
+	case *passthrough.PassthroughBlock:
+		for i := range nn.Lines().Len() {
+			line := nn.Lines().At(i)
+			w.Write(line.Value(src))
+		}
+	}
+	return ast.WalkSkipChildren, nil
+}
+
 var whiteSpaceRe = regexp.MustCompile(`\s+`)
 
 // sanitizeTOCHeadingTitle sanitizes s for use as a TOC heading title.

markup/goldmark/toc_integration_test.go

@@ -364,3 +364,37 @@ title: home
 		`<li><a href="#1st">1^st^</a></li>`,
 	)
 }
+
+// Issue 14677
+func TestTableOfContentsWithPassthrough(t *testing.T) {
+	t.Parallel()
+
+	files := `
+-- hugo.toml --
+disableKinds = ['page','rss','section','sitemap','taxonomy','term']
+[markup.goldmark.extensions.passthrough]
+  enable = true
+[markup.goldmark.extensions.passthrough.delimiters]
+  inline = [['$', '$']]
+-- content/_index.md --
+---
+title: home
+---
+## Heading with **$a$**
+
+## Heading with $b$
+
+## Heading with *$x + y$*
+
+-- layouts/home.html --
+{{ .TableOfContents }}
+`
+
+	b := hugolib.Test(t, files)
+
+	b.AssertFileContent("public/index.html",
+		`<li><a href="#heading-with">Heading with <strong>$a$</strong></a></li>`,
+		`<li><a href="#heading-with-1">Heading with $b$</a></li>`,
+		`<li><a href="#heading-with-2">Heading with <em>$x + y$</em></a></li>`,
+	)
+}