vdoc: support for highlighting code in README's (#19725)

cmd/tools/vdoc/html.v

@@ -393,7 +393,12 @@ fn doc_node_html(dn doc.DocNode, link string, head bool, include_examples bool,
 	} else {
 		html_tag_escape(comments)
 	}
-	md_content := markdown.to_html(escaped_html)
+	mut renderer := markdown.HtmlRenderer{
+		transformer: &MdHtmlCodeHighlighter{
+			table: tb
+		}
+	}
+	md_content := markdown.render(escaped_html, mut renderer) or { '' }
 	highlighted_code := html_highlight(dn.content, tb)
 	node_class := if dn.kind == .const_group { ' const' } else { '' }
 	sym_name := get_sym_name(dn)
@@ -514,3 +519,28 @@ fn write_toc(dn doc.DocNode, mut toc strings.Builder) {
 fn no_quotes(s string) string {
 	return s.replace_each(no_quotes_replacement)
 }
+
+struct MdHtmlCodeHighlighter {
+mut:
+	language string
+	table    &ast.Table
+}
+
+fn (f &MdHtmlCodeHighlighter) transform_attribute(p markdown.ParentType, name string, value string) string {
+	return markdown.default_html_transformer.transform_attribute(p, name, value)
+}
+
+fn (f &MdHtmlCodeHighlighter) transform_content(parent markdown.ParentType, text string) string {
+	if parent is markdown.MD_BLOCKTYPE && parent == .md_block_code {
+		if f.language == 'v' || f.language == 'vlang' {
+			return html_highlight(text, f.table)
+		}
+	}
+	return markdown.default_html_transformer.transform_content(parent, text)
+}
+
+fn (mut f MdHtmlCodeHighlighter) config_set(key string, val string) {
+	if key == 'code_language' {
+		f.language = val
+	}
+}