[Element][SSR] Set class expression if spread is used

src/compiler/compile/render_ssr/handlers/Element.ts

@@ -109,6 +109,9 @@ export default function(node: Element, renderer: Renderer, options: RenderOption
 				) {
 					// a boolean attribute with one non-Text chunk
 					args.push(`{ ${quote_name_if_necessary(attribute.name)}: ${snip(attribute.chunks[0])} }`);
+				} else if (attribute.name === 'class' && class_expression) {
+					// Add class expression
+					args.push(`{ ${quote_name_if_necessary(attribute.name)}: [\`${stringify_attribute(attribute, true)}\`, \`\${${class_expression}}\`].join(' ').trim() }`);
 				} else {
 					args.push(`{ ${quote_name_if_necessary(attribute.name)}: \`${stringify_attribute(attribute, true)}\` }`);
 				}