feat(runtime,jest,bridge): add console forwarding and batched state updates

Console Forwarding:
- Forward console.log/warn/error/info/debug from device to Jest output
- Add ConsoleEvent/ConsoleLevel types to BridgeEvents union
- Preserve Error details (stack/message) in forwarded output
- Fix %d printf placeholder to use Number() for decimals

Type Improvements:
- Remove type assertions in factory.ts with proper ConsoleEvent types
- Add proper generic constraints for Harness.on/off methods
- Import shared ConsoleEvent type in jest package

Shared Utilities:
- Extract batchedUpdate utility to avoid code duplication
- Add resetRenderState helper for common state reset pattern
- Simplify render/cleanup.ts using shared utilities

Author: bheemreddy-samsara

packages/bridge/src/shared.ts

@@ -4,6 +4,7 @@ import type {
 } from './shared/test-runner.js';
 import type { TestCollectorEvents } from './shared/test-collector.js';
 import type { BundlerEvents } from './shared/bundler.js';
+import type { ConsoleEvent } from './shared/console.js';
 import type { HarnessPlatform } from '@react-native-harness/platforms';
 
 export type FileReference = {
@@ -103,6 +104,7 @@ export type {
   SetupFileBundlingFailedEvent,
   BundlerEvents,
 } from './shared/bundler.js';
+export type { ConsoleEvent, ConsoleLevel } from './shared/console.js';
 
 export type DeviceDescriptor = {
   platform: 'ios' | 'android' | 'vega';
@@ -114,7 +116,8 @@ export type DeviceDescriptor = {
 export type BridgeEvents =
   | TestCollectorEvents
   | TestRunnerEvents
-  | BundlerEvents;
+  | BundlerEvents
+  | ConsoleEvent;
 
 export type BridgeEventsMap = {
   [K in BridgeEvents['type']]: (

packages/bridge/src/shared/console.ts

@@ -0,0 +1,8 @@
+export type ConsoleLevel = 'log' | 'warn' | 'error' | 'info' | 'debug';
+
+export type ConsoleEvent = {
+  type: 'console';
+  level: ConsoleLevel;
+  args: string[];
+  timestamp: number;
+};

packages/jest/src/harness.ts

@@ -1,6 +1,7 @@
 import {
   getBridgeServer,
   BridgeServer,
+  BridgeServerEvents,
 } from '@react-native-harness/bridge/server';
 import {
   HarnessContext,
@@ -31,6 +32,14 @@ export type Harness = {
   restart: () => Promise<void>;
   dispose: () => Promise<void>;
   crashMonitor: CrashMonitor;
+  on: <T extends keyof BridgeServerEvents>(
+    event: T,
+    handler: BridgeServerEvents[T]
+  ) => void;
+  off: <T extends keyof BridgeServerEvents>(
+    event: T,
+    handler: BridgeServerEvents[T]
+  ) => void;
 };
 
 export const waitForAppReady = async (options: {
@@ -205,6 +214,8 @@ const getHarnessInternal = async (
     restart,
     dispose,
     crashMonitor,
+    on: (event, handler) => serverBridge.on(event, handler),
+    off: (event, handler) => serverBridge.off(event, handler),
   };
 };
 

packages/jest/src/index.ts

@@ -9,6 +9,7 @@ import type {
   TestWatcher,
 } from 'jest-runner';
 import pLimit from 'p-limit';
+import chalk from 'chalk';
 import { runHarnessTestFile } from './run.js';
 import { Config as HarnessConfig } from '@react-native-harness/config';
 import { type Harness } from './harness.js';
@@ -18,6 +19,72 @@ import { HarnessError } from '@react-native-harness/tools';
 import { getErrorMessage } from './logs.js';
 import { DeviceNotRespondingError } from '@react-native-harness/bridge/server';
 import { NativeCrashError } from './errors.js';
+import { ConsoleEvent } from '@react-native-harness/bridge';
+
+// Printf-style string interpolation for console messages
+const formatConsoleMessage = (args: string[]): string => {
+  if (!args || args.length === 0) return '';
+  if (args.length === 1) return args[0];
+
+  let template = String(args[0]);
+  let argIndex = 1;
+
+  // Replace %s, %d, %i, %o, %O, %j with corresponding arguments
+  template = template.replace(/%[sdioOj]/g, (match) => {
+    if (argIndex >= args.length) return match;
+    const arg = args[argIndex++];
+    switch (match) {
+      case '%s':
+        return String(arg);
+      case '%d':
+        return String(Number(arg));
+      case '%i':
+        return String(parseInt(String(arg), 10));
+      case '%o':
+      case '%O':
+      case '%j':
+        return typeof arg === 'string' ? arg : JSON.stringify(arg);
+      default:
+        return String(arg);
+    }
+  });
+
+  // Append remaining arguments
+  const remaining = args.slice(argIndex);
+  if (remaining.length > 0) {
+    template += ' ' + remaining.join(' ');
+  }
+
+  return template;
+};
+
+// Console event handler - prints console messages from device
+const createConsoleEventHandler = (): ((event: ConsoleEvent) => void) => {
+  return (event: ConsoleEvent) => {
+    if (event.type === 'console') {
+      const message = formatConsoleMessage(event.args);
+      const tags: Record<string, string> = {
+        log: chalk.supportsColor
+          ? chalk.reset.inverse.bold.cyan(' LOG ')
+          : 'LOG',
+        warn: chalk.supportsColor
+          ? chalk.reset.inverse.bold.yellow(' WARN ')
+          : 'WARN',
+        error: chalk.supportsColor
+          ? chalk.reset.inverse.bold.red(' ERROR ')
+          : 'ERROR',
+        info: chalk.supportsColor
+          ? chalk.reset.inverse.bold.blue(' INFO ')
+          : 'INFO',
+        debug: chalk.supportsColor
+          ? chalk.reset.inverse.bold.gray(' DEBUG ')
+          : 'DEBUG',
+      };
+      const tag = tags[event.level] || tags.log;
+      process.stderr.write(`${tag} ${message}\n`);
+    }
+  };
+};
 
 class CancelRun extends Error {
   constructor(message?: string) {
@@ -47,13 +114,21 @@ export default class JestHarness implements CallbackTestRunnerInterface {
       throw new Error('Parallel test running is not supported');
     }
 
+    let consoleHandler: ((event: ConsoleEvent) => void) | null = null;
+
     try {
       // This is necessary as Harness may throw and we want to catch it and display a helpful error message.
       await setup(this.#globalConfig);
 
       const harness = global.HARNESS;
       const harnessConfig = global.HARNESS_CONFIG;
 
+      // Setup console forwarding if not in silent mode
+      if (!this.#globalConfig.silent) {
+        consoleHandler = createConsoleEventHandler();
+        harness.on('event', consoleHandler);
+      }
+
       return await this._createInBandTestRun(
         tests,
         watcher,
@@ -71,6 +146,10 @@ export default class JestHarness implements CallbackTestRunnerInterface {
 
       throw error;
     } finally {
+      // Cleanup console handler
+      if (consoleHandler && global.HARNESS) {
+        global.HARNESS.off('event', consoleHandler);
+      }
       // This is necessary as Harness may throw and we want to catch it and display a helpful error message.
       await teardown(this.#globalConfig);
     }

packages/runtime/src/client/factory.ts

@@ -3,6 +3,8 @@ import type {
   TestCollectorEvents,
   BundlerEvents,
   TestExecutionOptions,
+  ConsoleLevel,
+  ConsoleEvent,
 } from '@react-native-harness/bridge';
 import { getBridgeClient } from '@react-native-harness/bridge/client';
 import { store } from '../ui/state.js';
@@ -16,6 +18,61 @@ import { setup } from '../render/setup.js';
 import { runSetupFiles } from './setup-files.js';
 import { setClient } from './store.js';
 
+type EmitEventFn = (type: ConsoleEvent['type'], data: ConsoleEvent) => void;
+
+// Console forwarding setup - intercepts console calls and emits events to host
+const setupConsoleForwarding = (emitEvent: EmitEventFn): (() => void) => {
+  const originalConsole: Record<ConsoleLevel, typeof console.log> = {
+    log: console.log,
+    warn: console.warn,
+    error: console.error,
+    info: console.info,
+    debug: console.debug,
+  };
+
+  const createForwarder =
+    (level: ConsoleLevel) =>
+    (...args: unknown[]) => {
+      // Call original console method
+      originalConsole[level](...args);
+
+      // Forward to host via bridge
+      try {
+        emitEvent('console', {
+          type: 'console',
+          level,
+          args: args.map((arg) => {
+            try {
+              if (arg instanceof Error) {
+                return arg.stack ?? `${arg.name}: ${arg.message}`;
+              }
+              if (typeof arg === 'object' && arg !== null) {
+                return JSON.stringify(arg);
+              }
+              return String(arg);
+            } catch {
+              return String(arg);
+            }
+          }),
+          timestamp: Date.now(),
+        });
+      } catch {
+        // Ignore errors during forwarding to avoid infinite loops
+      }
+    };
+
+  console.log = createForwarder('log');
+  console.warn = createForwarder('warn');
+  console.error = createForwarder('error');
+  console.info = createForwarder('info');
+  console.debug = createForwarder('debug');
+
+  // Return cleanup function to restore original console
+  return () => {
+    Object.assign(console, originalConsole);
+  };
+};
+
 export const getClient = async () => {
   const client = await getBridgeClient(getWSServer(), {
     runTests: async () => {
@@ -41,6 +98,7 @@ export const getClient = async () => {
       TestRunnerEvents | TestCollectorEvents | BundlerEvents
     > | null = null;
     let bundler: Bundler | null = null;
+    let cleanupConsole: (() => void) | null = null;
 
     try {
       collector = getTestCollector();
@@ -56,6 +114,11 @@ export const getClient = async () => {
         client.rpc.emitEvent(event.type, event);
       });
 
+      // Setup console forwarding to emit console events to host
+      cleanupConsole = setupConsoleForwarding((type, data) => {
+        client.rpc.emitEvent(type, data);
+      });
+
       await runSetupFiles({
         setupFiles: options.setupFiles ?? [],
         setupFilesAfterEnv: [],
@@ -94,6 +157,8 @@ export const getClient = async () => {
       });
       return result;
     } finally {
+      // Restore original console
+      cleanupConsole?.();
       collector?.dispose();
       runner?.dispose();
       events?.clearAllListeners();

packages/runtime/src/render/cleanup.ts

@@ -1,7 +1,5 @@
-import { store } from '../ui/state.js';
+import { resetRenderState } from './utils.js';
 
 export const cleanup = (): void => {
-  store.getState().setRenderedElement(null);
-  store.getState().setOnLayoutCallback(null);
-  store.getState().setOnRenderCallback(null);
+  resetRenderState();
 };

packages/runtime/src/render/index.ts

@@ -1,5 +1,7 @@
 import React from 'react';
 import { store } from '../ui/state.js';
+import { batchedUpdate } from '../utils/batchedUpdate.js';
+import { resetRenderState } from './utils.js';
 import type { RenderResult, RenderOptions } from './types.js';
 
 const wrapElement = (
@@ -20,9 +22,7 @@ export const render = async (
 
   // If an element is already rendered, unmount it first
   if (store.getState().renderedElement !== null) {
-    store.getState().setRenderedElement(null);
-    store.getState().setOnLayoutCallback(null);
-    store.getState().setOnRenderCallback(null);
+    resetRenderState();
   }
 
   // Create a promise that resolves when the element is rendered.
@@ -36,15 +36,19 @@ export const render = async (
       );
     }, timeout);
 
-    store.getState().setOnRenderCallback(() => {
-      clearTimeout(timeoutId);
-      resolve();
+    batchedUpdate(() => {
+      store.getState().setOnRenderCallback(() => {
+        clearTimeout(timeoutId);
+        resolve();
+      });
     });
   });
 
   // Wrap and set the element in state (key is generated automatically)
   const wrappedElement = wrapElement(element, wrapper);
-  store.getState().setRenderedElement(wrappedElement);
+  batchedUpdate(() => {
+    store.getState().setRenderedElement(wrappedElement);
+  });
 
   // Wait for useEffect to fire, ensuring all children are committed
   await renderPromise;
@@ -65,14 +69,18 @@ export const render = async (
         );
       }, timeout);
 
-      store.getState().setOnRenderCallback(() => {
-        clearTimeout(timeoutId);
-        resolve();
+      batchedUpdate(() => {
+        store.getState().setOnRenderCallback(() => {
+          clearTimeout(timeoutId);
+          resolve();
+        });
       });
     });
 
     const wrappedNewElement = wrapElement(newElement, wrapper);
-    store.getState().updateRenderedElement(wrappedNewElement);
+    batchedUpdate(() => {
+      store.getState().updateRenderedElement(wrappedNewElement);
+    });
 
     // Wait for render
     await renderPromise;
@@ -82,10 +90,7 @@ export const render = async (
     if (store.getState().renderedElement === null) {
       return;
     }
-
-    store.getState().setRenderedElement(null);
-    store.getState().setOnLayoutCallback(null);
-    store.getState().setOnRenderCallback(null);
+    resetRenderState();
   };
 
   return {

packages/runtime/src/render/utils.ts

@@ -0,0 +1,14 @@
+import { store } from '../ui/state.js';
+import { batchedUpdate } from '../utils/batchedUpdate.js';
+
+/**
+ * Resets render-related state in a batched update.
+ * Clears the rendered element and associated callbacks.
+ */
+export const resetRenderState = (): void => {
+  batchedUpdate(() => {
+    store.getState().setRenderedElement(null);
+    store.getState().setOnLayoutCallback(null);
+    store.getState().setOnRenderCallback(null);
+  });
+};

packages/runtime/src/utils/batchedUpdate.ts

@@ -0,0 +1,13 @@
+import { unstable_batchedUpdates } from 'react-native';
+
+/**
+ * Batches state updates to avoid act() warnings in React Native.
+ * Falls back to direct execution if unstable_batchedUpdates is unavailable.
+ */
+export const batchedUpdate = (fn: () => void): void => {
+  if (unstable_batchedUpdates) {
+    unstable_batchedUpdates(fn);
+  } else {
+    fn();
+  }
+};