fix: modify ssg default rendering mode

Author: yimingjfe

packages/cli/plugin-ssg/src/server/index.ts

@@ -120,6 +120,7 @@ export const createServer = async (
           method: 'GET',
           headers: {
             host: 'localhost',
+            'x-modern-ssg-render': 'true',
           },
         });
 

packages/runtime/plugin-runtime/src/cli/code.ts

@@ -1,6 +1,5 @@
 import path from 'path';
 import type {
-  AppNormalizedConfig,
   AppToolsContext,
   AppToolsFeatureHooks,
   AppToolsNormalizedConfig,
@@ -17,32 +16,15 @@ import {
   INDEX_FILE_NAME,
   SERVER_ENTRY_POINT_FILE_NAME,
 } from './constants';
+import { resolveSSRMode } from './ssr/mode';
 import * as template from './template';
 import * as serverTemplate from './template.server';
 
 function getSSRMode(
   entry: string,
   config: AppToolsNormalizedConfig,
 ): 'string' | 'stream' | false {
-  const { ssr, ssrByEntries } = config.server;
-
-  if (config.output.ssg || config.output.ssgByEntries) {
-    return 'string';
-  }
-
-  return checkSSRMode(ssrByEntries?.[entry] || ssr);
-
-  function checkSSRMode(ssr: AppNormalizedConfig['server']['ssr']) {
-    if (!ssr) {
-      return false;
-    }
-
-    if (typeof ssr === 'boolean') {
-      return ssr ? 'string' : false;
-    }
-
-    return ssr.mode === 'stream' ? 'stream' : 'string';
-  }
+  return resolveSSRMode({ entry, config });
 }
 
 export const generateCode = async (

packages/runtime/plugin-runtime/src/cli/ssr/index.ts

@@ -8,6 +8,7 @@ import type {
 import type { CLIPluginAPI } from '@modern-js/plugin';
 import { LOADABLE_STATS_FILE, isUseSSRBundle } from '@modern-js/utils';
 import type { RsbuildPlugin } from '@rsbuild/core';
+import { resolveSSRMode } from './mode';
 
 const hasStringSSREntry = (userConfig: AppToolsNormalizedConfig): boolean => {
   const isStreaming = (ssr: ServerUserConfig['ssr']) =>
@@ -42,16 +43,12 @@ const hasStringSSREntry = (userConfig: AppToolsNormalizedConfig): boolean => {
   return false;
 };
 
-const checkUseStringSSR = (config: AppToolsNormalizedConfig): boolean => {
-  const { output } = config;
-
-  if (output?.ssg) {
-    return true;
-  }
-  if (output?.ssgByEntries && Object.keys(output.ssgByEntries).length > 0) {
-    return true;
-  }
-  return hasStringSSREntry(config);
+const checkUseStringSSR = (
+  config: AppToolsNormalizedConfig,
+  appDirectory?: string,
+): boolean => {
+  const ssrMode = resolveSSRMode({ config, appDirectory });
+  return ssrMode === 'string';
 };
 
 const ssrBuilderPlugin = (
@@ -72,10 +69,13 @@ const ssrBuilderPlugin = (
           ? 'edge'
           : 'node';
 
+      const appContext = modernAPI.getAppContext();
+      const { appDirectory } = appContext;
+
       const useLoadablePlugin =
         isUseSSRBundle(userConfig) &&
         !isServerEnvironment &&
-        checkUseStringSSR(userConfig);
+        checkUseStringSSR(userConfig, appDirectory);
 
       return mergeEnvironmentConfig(config, {
         source: {

packages/runtime/plugin-runtime/src/cli/ssr/mode.ts

@@ -0,0 +1,63 @@
+import type {
+  AppNormalizedConfig,
+  AppToolsNormalizedConfig,
+} from '@modern-js/app-tools';
+import { isReact18, isUseRsc } from '@modern-js/utils';
+
+export type SSRMode = 'string' | 'stream' | false;
+
+/**
+ * Unified SSR mode resolution function.
+ * Priority:
+ * 1. User's explicit server.ssr/server.ssrByEntries config
+ * 2. If RSC is enabled, use 'stream'
+ * 3. If SSG is enabled, use 'stream' for React 18+, 'string' otherwise
+ * 4. Otherwise return false (no SSR)
+ */
+export function resolveSSRMode(params: {
+  entry?: string;
+  config: AppToolsNormalizedConfig;
+  appDirectory?: string;
+}): SSRMode {
+  const { entry, config, appDirectory } = params;
+
+  // 1. Check user's explicit SSR config (server.ssr or server.ssrByEntries)
+  const ssr = entry
+    ? config.server?.ssrByEntries?.[entry] || config.server?.ssr
+    : config.server?.ssr;
+
+  if (ssr !== undefined) {
+    if (!ssr) {
+      return false;
+    }
+    if (typeof ssr === 'boolean') {
+      return ssr ? 'string' : false;
+    }
+    return ssr.mode === 'stream' ? 'stream' : 'string';
+  }
+
+  // 2. If RSC is enabled, use streaming SSR
+  if (isUseRsc(config)) {
+    return 'stream';
+  }
+
+  // 3. If SSG is enabled, check React version
+  const isSsgEnabled =
+    config.output?.ssg ||
+    (config.output?.ssgByEntries &&
+      (entry
+        ? !!config.output.ssgByEntries[entry]
+        : Object.keys(config.output.ssgByEntries).length > 0));
+
+  if (isSsgEnabled) {
+    // React 18+ supports streaming SSR
+    if (appDirectory) {
+      return isReact18(appDirectory) ? 'stream' : 'string';
+    }
+    // Default to React 18+ when appDirectory is not available
+    return 'stream';
+  }
+
+  // 4. No SSR
+  return false;
+}

packages/runtime/plugin-runtime/src/core/server/requestHandler.tsx

@@ -10,7 +10,7 @@ import {
   parseHeaders,
   parseQuery,
 } from '@modern-js/runtime-utils/universal/request';
-import type React from 'react';
+import React from 'react';
 import { Fragment } from 'react';
 import {
   type RuntimeContext,
@@ -143,7 +143,13 @@ function createSSRContext(
     config.ssr,
     config.ssrByEntries,
   );
-  const ssrMode = getSSRMode(ssrConfig);
+  let ssrMode = getSSRMode(ssrConfig);
+
+  const isSsgRender = headers.get('x-modern-ssg-render') === 'true';
+  if (isSsgRender) {
+    const reactMajor = Number((React.version || '0').split('.')[0]);
+    ssrMode = reactMajor >= 18 ? 'stream' : 'string';
+  }
 
   const loaderFailureMode =
     typeof ssrConfig === 'object' ? ssrConfig.loaderFailureMode : undefined;

packages/runtime/plugin-runtime/src/core/server/stream/createReadableStream.ts

@@ -36,7 +36,11 @@ export const createReadableStreamFromElement: CreateReadableStreamFromElement =
     // When a crawler visit the page, we should waiting for entrie content of page
 
     const isbot = checkIsBot(request.headers.get('user-agent'));
-    const onReady = isbot || forceStream2String ? 'onAllReady' : 'onShellReady';
+    const isSsgRender = request.headers.get('x-modern-ssg-render') === 'true';
+    const onReady =
+      isbot || isSsgRender || forceStream2String
+        ? 'onAllReady'
+        : 'onShellReady';
 
     const internalRuntimeContext = getGlobalInternalRuntimeContext();
     const hooks = internalRuntimeContext.hooks;

packages/runtime/plugin-runtime/src/core/server/stream/createReadableStream.worker.ts

@@ -56,8 +56,9 @@ export const createReadableStreamFromElement: CreateReadableStreamFromElement =
       });
 
       const isbot = checkIsBot(request.headers.get('user-agent'));
-      if (isbot) {
-        // However, when a crawler visits your page, or if you’re generating the pages at the build time,
+      const isSsgRender = request.headers.get('x-modern-ssg-render') === 'true';
+      if (isbot || isSsgRender) {
+        // However, when a crawler visits your page, or if you're generating the pages at the build time,
         // you might want to let all of the content load first and then produce the final HTML output instead of revealing it progressively.
         // from: https://react.dev/reference/react-dom/server/renderToReadableStream#handling-different-errors-in-different-ways
         await readableOriginal.allReady;

packages/runtime/plugin-runtime/src/router/cli/code/index.ts

@@ -16,7 +16,6 @@ import type {
 import {
   fs,
   getEntryOptions,
-  isSSGEntry,
   isUseRsc,
   isUseSSRBundle,
   logger,
@@ -28,6 +27,7 @@ import {
 } from '@modern-js/utils';
 import { cloneDeep } from '@modern-js/utils/lodash';
 import { ENTRY_POINT_RUNTIME_GLOBAL_CONTEXT_FILE_NAME } from '../../../cli/constants';
+import { resolveSSRMode } from '../../../cli/ssr/mode';
 import { FILE_SYSTEM_ROUTES_FILE_NAME } from '../constants';
 import { walk } from './nestedRoutes';
 import * as templates from './templates';
@@ -173,14 +173,19 @@ export const generateCode = async (
           config.server.ssrByEntries,
           packageName,
         );
-        const useSSG = isSSGEntry(config, entryName, entrypoints);
 
         let mode: SSRMode | undefined;
         if (ssr) {
           mode = typeof ssr === 'object' ? ssr.mode || 'string' : 'string';
         }
 
-        if (mode === 'stream') {
+        const ssrMode = resolveSSRMode({
+          entry: entrypoint.entryName,
+          config,
+          appDirectory: appContext.appDirectory,
+        });
+
+        if (ssrMode === 'stream') {
           const hasPageRoute = routes.some(
             route => 'type' in route && route.type === 'page',
           );
@@ -197,7 +202,7 @@ export const generateCode = async (
           code: await templates.fileSystemRoutes({
             metaName,
             routes: routes,
-            ssrMode: useSSG ? 'string' : isUseRsc(config) ? 'stream' : mode,
+            ssrMode,
             nestedRoutesEntry: entrypoint.nestedRoutesEntry,
             entryName: entrypoint.entryName,
             internalDirectory,
@@ -233,7 +238,7 @@ export const generateCode = async (
           const serverRoutesCode = await templates.fileSystemRoutes({
             metaName,
             routes: filtedRoutesForServer,
-            ssrMode: useSSG ? 'string' : mode,
+            ssrMode,
             nestedRoutesEntry: entrypoint.nestedRoutesEntry,
             entryName: entrypoint.entryName,
             internalDirectory,