Add mermaid tiptap extension

Signed-off-by: Émile Ré <emile@getprobo.com>

pkg/prosemirror/html.go

@@ -71,15 +71,23 @@ func renderNode(buf *bytes.Buffer, n Node) error {
 		if err != nil {
 			return fmt.Errorf("cannot render code block node: %w", err)
 		}
-		buf.WriteString("<pre><code")
-		if attrs.Language != nil {
-			writeAttr(buf, "class", "language-"+*attrs.Language)
+		if attrs.Language != nil && *attrs.Language == "mermaid" {
+			buf.WriteString(`<pre class="mermaid">`)
+			if err := renderChildren(buf, n.Content); err != nil {
+				return err
+			}
+			buf.WriteString("</pre>")
+		} else {
+			buf.WriteString("<pre><code")
+			if attrs.Language != nil {
+				writeAttr(buf, "class", "language-"+*attrs.Language)
+			}
+			buf.WriteByte('>')
+			if err := renderChildren(buf, n.Content); err != nil {
+				return err
+			}
+			buf.WriteString("</code></pre>")
 		}
-		buf.WriteByte('>')
-		if err := renderChildren(buf, n.Content); err != nil {
-			return err
-		}
-		buf.WriteString("</code></pre>")
 	case NodeHorizontalRule:
 		buf.WriteString("<hr>")
 	case NodeHardBreak:

pkg/prosemirror/html_test.go

@@ -100,6 +100,18 @@ func TestRenderHTML_CodeBlockWithLanguage(t *testing.T) {
 	assert.Equal(t, `<pre><code class="language-go">fmt.Println()</code></pre>`, got)
 }
 
+func TestRenderHTML_CodeBlockMermaid(t *testing.T) {
+	t.Parallel()
+
+	raw := `{"type":"codeBlock","attrs":{"language":"mermaid"},"content":[{"type":"text","text":"graph TD\n  A-->B"}]}`
+	var n Node
+	require.NoError(t, json.Unmarshal([]byte(raw), &n))
+
+	got, err := RenderHTML(n)
+	require.NoError(t, err)
+	assert.Equal(t, "<pre class=\"mermaid\">graph TD\n  A--&gt;B</pre>", got)
+}
+
 func TestRenderHTML_CodeBlockWithoutLanguage(t *testing.T) {
 	t.Parallel()