fix(runtime): validate preact class component output

Author: unadlib

packages/runtime/src/runtime-component-runtime.ts

@@ -23,6 +23,12 @@ type PreactLikeModule = {
   h(type: unknown, props: unknown, ...children: unknown[]): unknown;
 };
 
+type PreactLikeClassComponent = new (
+  ...args: unknown[]
+) => {
+  render(...args: unknown[]): unknown;
+};
+
 export type RuntimeComponentFactory = (
   props: Record<string, JsonValue>,
   context: RuntimeExecutionContext,
@@ -73,7 +79,7 @@ export async function createPreactRenderArtifact(input: {
 
   try {
     const component = isPreactClassComponent(input.sourceExport)
-      ? input.sourceExport
+      ? wrapPreactClassComponent(input.sourceExport as PreactLikeClassComponent)
       : wrapPreactFunctionComponent(
           input.sourceExport as (props: Record<string, JsonValue>) => unknown,
         );
@@ -235,6 +241,22 @@ function isPreactClassComponent(value: unknown): boolean {
   return typeof prototype?.render === "function";
 }
 
+function wrapPreactClassComponent(
+  sourceComponent: PreactLikeClassComponent,
+): PreactLikeClassComponent {
+  return class RenderifyPreactSourceClassWrapper extends sourceComponent {
+    render(...args: unknown[]): unknown {
+      const output = super.render(...args);
+      if (isPlainObjectPreactOutput(output)) {
+        throw new Error(
+          'source.runtime=preact component returned a plain object; return JSX/h() output or use source.runtime="renderify"',
+        );
+      }
+      return output;
+    }
+  };
+}
+
 function wrapPreactFunctionComponent(
   sourceComponent: (props: Record<string, JsonValue>) => unknown,
 ): (props: Record<string, JsonValue>) => unknown {

tests/runtime.test.ts

@@ -3266,6 +3266,50 @@ test("runtime preact rendering rejects plain object component output", async ()
   await runtime.terminate();
 });
 
+test("runtime preact rendering rejects plain object class component output", async () => {
+  const runtime = new DefaultRuntimeManager({
+    sourceTranspiler: new PassthroughSourceTranspiler(),
+  });
+  await runtime.initialize();
+
+  const plan: RuntimePlan = {
+    specVersion: DEFAULT_RUNTIME_PLAN_SPEC_VERSION,
+    id: "runtime_preact_plain_object_class_output_plan",
+    version: 1,
+    root: createElementNode("div", undefined, [createTextNode("fallback")]),
+    capabilities: {
+      domWrite: true,
+    },
+    state: {
+      initial: {
+        count: 4,
+      },
+    },
+    source: {
+      language: "js",
+      runtime: "preact",
+      code: [
+        'import { Component } from "preact";',
+        "export default class Dashboard extends Component {",
+        "  render(props) {",
+        '    return { type: "section", props: { "data-kind": "dashboard" },',
+        "      children: [`count:${props.state.count}`] };",
+        "  }",
+        "}",
+      ].join("\n"),
+    },
+  };
+
+  const result = await runtime.executePlan(plan);
+  assert.equal(result.renderArtifact?.mode, "preact-vnode");
+  await assert.rejects(
+    () => new DefaultUIRenderer().render(result),
+    /plain object/,
+  );
+
+  await runtime.terminate();
+});
+
 test("runtime can fail-fast on dependency preflight import errors", async () => {
   const runtime = new DefaultRuntimeManager({
     moduleLoader: new FailingLoader(),