Diff to override goldmark's code block output

markdown.diff

diff --git a/internal/markdown/markdown.go b/internal/markdown/markdown.go
index a729b9f..94d29c1 100644
--- a/internal/markdown/markdown.go
+++ b/internal/markdown/markdown.go
@@ -13,8 +13,11 @@ import (
 	"bytes"
 
 	"github.com/yuin/goldmark"
+	"github.com/yuin/goldmark/ast"
 	"github.com/yuin/goldmark/parser"
+	"github.com/yuin/goldmark/renderer"
 	"github.com/yuin/goldmark/renderer/html"
+	"github.com/yuin/goldmark/util"
 )
 
 // Render converts a limited and opinionated flavor of Markdown (compliant with
@@ -25,14 +28,65 @@ import (
 // untrusted content is not performed: the caller is responsible for ensuring
 // that only trusted content is provided.
 func Render(src []byte) ([]byte, error) {
+	hr := html.NewRenderer(html.WithUnsafe())
+	nr := &CustomNodeRenderer{hr, html.DefaultWriter}
+	r := renderer.NewRenderer(renderer.WithNodeRenderers(util.Prioritized(nr, 1000)))
+
 	// parser.WithHeadingAttribute allows custom ids on headings.
 	// html.WithUnsafe allows use of raw HTML, which we need for tables.
 	md := goldmark.New(
 		goldmark.WithParserOptions(parser.WithHeadingAttribute()),
-		goldmark.WithRendererOptions(html.WithUnsafe()))
+		goldmark.WithRenderer(r))
 	var buf bytes.Buffer
 	if err := md.Convert(src, &buf); err != nil {
 		return nil, err
 	}
 	return buf.Bytes(), nil
 }
+
+type CustomNodeRenderer struct {
+	nr     renderer.NodeRenderer
+	Writer html.Writer
+}
+
+func (r *CustomNodeRenderer) RegisterFuncs(reg renderer.NodeRendererFuncRegisterer) {
+	r.nr.RegisterFuncs(reg)
+	reg.Register(ast.KindCodeBlock, r.renderCodeBlock)
+	reg.Register(ast.KindFencedCodeBlock, r.renderFencedCodeBlock)
+}
+
+func (r *CustomNodeRenderer) renderCodeBlock(w util.BufWriter, source []byte, n ast.Node, entering bool) (ast.WalkStatus, error) {
+	if entering {
+		_, _ = w.WriteString("<pre>")
+		r.writeLines(w, source, n)
+	} else {
+		_, _ = w.WriteString("</pre>\n")
+	}
+	return ast.WalkContinue, nil
+}
+
+func (r *CustomNodeRenderer) renderFencedCodeBlock(w util.BufWriter, source []byte, node ast.Node, entering bool) (ast.WalkStatus, error) {
+	n := node.(*ast.FencedCodeBlock)
+	if entering {
+		_, _ = w.WriteString("<pre")
+		language := n.Language(source)
+		if language != nil {
+			_, _ = w.WriteString(" class=\"language-")
+			r.Writer.Write(w, language)
+			_, _ = w.WriteString("\"")
+		}
+		_ = w.WriteByte('>')
+		r.writeLines(w, source, n)
+	} else {
+		_, _ = w.WriteString("</pre>\n")
+	}
+	return ast.WalkContinue, nil
+}
+
+func (r *CustomNodeRenderer) writeLines(w util.BufWriter, source []byte, n ast.Node) {
+	l := n.Lines().Len()
+	for i := 0; i < l; i++ {
+		line := n.Lines().At(i)
+		r.Writer.RawWrite(w, line.Value(source))
+	}
+}