Add configurable CodeClassPrefix option for HTML renderer

README.md

@@ -160,6 +160,7 @@ Parser and Renderer options
 | `html.WithHardWraps` | `-` | Render newlines as `<br>`.|
 | `html.WithXHTML` | `-` | Render as XHTML. |
 | `html.WithUnsafe` | `-` | By default, goldmark does not render raw HTML or potentially dangerous links. With this option, goldmark renders such content as written. |
+| `html.WithCodeClassPrefix` | `string` | Sets a custom prefix for the `class` attribute of `<code>` elements. An empty string removes the prefix. |
 
 ### Built-in extensions
 

extra_test.go

@@ -219,3 +219,41 @@ func TestDangerousURLStringCase(t *testing.T) {
 		t.Error("Dangerous URL should ignore cases:\n" + string(testutil.DiffPretty(expected, b.Bytes())))
 	}
 }
+
+func TestCodeClassPrefix(t *testing.T) {
+	cases := []struct {
+		prefix   string
+		source   string
+		expected string
+	}{
+		{
+			prefix:   "language-",
+			source:   "```go\ncode\n```",
+			expected: "<pre><code class=\"language-go\">code\n</code></pre>\n",
+		},
+		{
+			prefix:   "custom-",
+			source:   "```go\ncode\n```",
+			expected: "<pre><code class=\"custom-go\">code\n</code></pre>\n",
+		},
+		{
+			prefix:   "",
+			source:   "```go\ncode\n```",
+			expected: "<pre><code class=\"go\">code\n</code></pre>\n",
+		},
+	}
+
+	for _, c := range cases {
+		markdown := New(WithRendererOptions(
+			html.WithCodeClassPrefix(c.prefix),
+		))
+		var b bytes.Buffer
+		err := markdown.Convert([]byte(c.source), &b)
+		if err != nil {
+			t.Errorf("unexpected error: %v", err)
+		}
+		if b.String() != c.expected {
+			t.Errorf("prefix: %q\nsource: %q\nexpected: %q\ngot: %q", c.prefix, c.source, c.expected, b.String())
+		}
+	}
+}

renderer/html/html.go

@@ -20,8 +20,12 @@ type Config struct {
 	EastAsianLineBreaks EastAsianLineBreaks
 	XHTML               bool
 	Unsafe              bool
+	CodeClassPrefix     string
 }
 
+// Default class prefix for <code> elements.
+const DefaultCodeClassPrefix = "language-"
+
 // NewConfig returns a new Config with defaults.
 func NewConfig() Config {
 	return Config{
@@ -30,6 +34,7 @@ func NewConfig() Config {
 		EastAsianLineBreaks: EastAsianLineBreaksNone,
 		XHTML:               false,
 		Unsafe:              false,
+		CodeClassPrefix:     DefaultCodeClassPrefix,
 	}
 }
 
@@ -46,6 +51,8 @@ func (c *Config) SetOption(name renderer.OptionName, value interface{}) {
 		c.Unsafe = value.(bool)
 	case optTextWriter:
 		c.Writer = value.(Writer)
+	case optCodeClassPrefix:
+		c.CodeClassPrefix = value.(string)
 	}
 }
 
@@ -240,6 +247,29 @@ func WithUnsafe() interface {
 	return &withUnsafe{}
 }
 
+// CodeClassPrefix is an option name used in WithCodeClassPrefix.
+const optCodeClassPrefix renderer.OptionName = "CodeClassPrefix"
+
+type withCodeClassPrefix struct {
+	value string
+}
+
+func (o *withCodeClassPrefix) SetConfig(c *renderer.Config) {
+	c.Options[optCodeClassPrefix] = o.value
+}
+
+func (o *withCodeClassPrefix) SetHTMLOption(c *Config) {
+	c.CodeClassPrefix = o.value
+}
+
+// WithCodeClassPrefix is a functional option to set the class prefix for <code> elements.
+func WithCodeClassPrefix(prefix string) interface {
+	renderer.Option
+	Option
+} {
+	return &withCodeClassPrefix{prefix}
+}
+
 // A Renderer struct is an implementation of renderer.NodeRenderer that renders
 // nodes as (X)HTML.
 type Renderer struct {
@@ -360,7 +390,8 @@ func (r *Renderer) renderFencedCodeBlock(
 		_, _ = w.WriteString("<pre><code")
 		language := n.Language(source)
 		if language != nil {
-			_, _ = w.WriteString(" class=\"language-")
+			_, _ = w.WriteString(" class=\"")
+			_, _ = w.WriteString(r.CodeClassPrefix)
 			r.Writer.Write(w, language)
 			_, _ = w.WriteString("\"")
 		}