修复 云端扩展框架仅在部署到可写的云环境时才输出缓存文件

uniCloud/cloudfunctions/common/uni-im-ext/index.js

@@ -67,6 +67,7 @@
 const fs = require('fs');
 const path = require('path');
 const REGISTER_EXT_CACHE = './_registered_ext.js'
+let isFsWritable = false
 
 function getSubdirs(parent) {
   try {
@@ -166,18 +167,26 @@ function loadExtensions() {
     requires.push(`const e_${extSeq} = require('${modDir.replace(/\\/g, '/')}');`)
     extSeq ++
   }
-  moduleExports = Object.keys(moduleExports).map(exp => {
-    return `"${exp}": [${moduleExports[exp].join(', ')}]`
-  }).join(',\n')
 
-  // 输出缓存文件
-  let registeredExtCache = `
+  // 把扫描到的扩展模块写入缓存文件
+  if (isFsWritable) {
+    moduleExports = Object.keys(moduleExports).map(exp => {
+      return `"${exp}": [${moduleExports[exp].join(', ')}]`
+    }).join(',\n')
+
+    try {
+      // 输出缓存文件
+      let registeredExtCache = `
 ${requires.join('\n')}
 module.exports = {
 ${moduleExports}
 }
 `
-  fs.writeFileSync(path.join(__dirname, REGISTER_EXT_CACHE), registeredExtCache)
+      fs.writeFileSync(path.join(__dirname, REGISTER_EXT_CACHE), registeredExtCache)
+    } catch (e) {
+      // 无法写缓存文件？
+    }
+  }
 
   return registeredExtensionPoints
 }
@@ -191,12 +200,19 @@ let _registeredExtensionPointsPromise
  * @returns {any[]} 该扩展点上挂接的所有扩展程序各自的返回值拼装在一个数组里。
  */
 async function invokeExts(extensionPointName, ...args) {
+  isFsWritable = (this.getCloudInfo().provider === 'aliyun')
+
   // 尝试从生成的缓存文件中加载
-  let registeredExtensionPoints = {}
-  try {
-    registeredExtensionPoints = require(REGISTER_EXT_CACHE)
-  } catch (e) {
-    // 尚无缓存
+  let registeredExtensionPoints
+  if (isFsWritable) {
+    try {
+      registeredExtensionPoints = require(REGISTER_EXT_CACHE)
+    } catch (e) {
+      // 尚未生成缓存文件
+    }
+  }
+
+  if (!registeredExtensionPoints) {
     // 懒加载，避免在调用接口重入时重复解析扩展模块
     if (!_registeredExtensionPointsPromise) {
       _registeredExtensionPointsPromise = new Promise(resolve => {
@@ -207,6 +223,7 @@ async function invokeExts(extensionPointName, ...args) {
   }
   // console.log('invokeExts:', Object.keys(registeredExtensionPoints), extensionPointName, args)
 
+  // 找到指定的扩展点并调用
   if (!registeredExtensionPoints[extensionPointName]) return []
   return Promise.all(
     registeredExtensionPoints[extensionPointName]