[wasm] fix #5021: wechat webassembly support

tfjs-backend-wasm/rollup.config.js

@@ -21,6 +21,7 @@ import node from '@rollup/plugin-node-resolve';
 import typescript from '@rollup/plugin-typescript';
 import visualizer from 'rollup-plugin-visualizer';
 import {getBrowserBundleConfigOptions} from '../rollup.config.helpers';
+import {patchWechatWebAssembly} from './scripts/patch-wechat-webassembly'
 
 const PREAMBLE = `/**
  * @license
@@ -143,7 +144,8 @@ module.exports = cmdOptions => {
         freeze: false
       },
       ignore: ['fs', 'path', 'worker_threads', 'perf_hooks', 'os'],
-      tsCompilerOptions: {target: 'es5'}
+      tsCompilerOptions: {target: 'es6'},
+      plugins: [ patchWechatWebAssembly() ]
     }));
   } else {
     const browserBundles = getBrowserBundleConfigOptions(

tfjs-backend-wasm/scripts/patch-wechat-webassembly.js

@@ -0,0 +1,40 @@
+/**
+ * WebAssembly has changed to WXWebAssembly after WeChat 8.0
+ * 0. not simd or thread support.
+ * 1. only load local wasm file is allowed.
+ * 2. WebAssembly.validate not working so env registerFlag doesn't work
+ * @see https://developers.weixin.qq.com/community/develop/doc/000e2c019f8a003d5dfbb54c251c00?jumpto=comment&commentid=000eac66934960576d0cb1a7256c
+ */
+ export function patchWechatWebAssembly() {
+  return {
+    transform(code, file) {
+      // remove node imports
+      if (
+        file.endsWith('tfjs-backend-wasm-threaded-simd.worker.js') ||
+        file.endsWith('tfjs-backend-wasm-threaded-simd.js')
+      ) {
+        code = code.replace(`require("worker_threads")`, 'null')
+        code = code.replace(`require("perf_hooks")`, 'null')
+      }
+
+      // it is not a nice way, but WebAssembly.validate not working and SIMD is not support in WXWebAssembly
+      if (file.endsWith('backend_wasm.ts')) {
+        code = code.replace(`env().getAsync('WASM_HAS_SIMD_SUPPORT')`, 'false')
+        code = code.replace(`env().getAsync('WASM_HAS_MULTITHREAD_SUPPORT')`, 'false')
+        code = code.replace(
+          `function createInstantiateWasmFunc(path) {`,
+          `function createInstantiateWasmFunc(path) {
+  return function (imports, callback) {
+    WebAssembly.instantiate(path, imports).then(function (output) {
+        callback(output.instance, output.module);
+    });
+    return {};
+  }`)
+      }
+
+      code = code.replace(`WebAssembly.`, `WXWebAssembly.`)
+      code = code.replace(`typeof WebAssembly`, `typeof WXWebAssembly`)
+      return { code };
+    }
+  }
+}

tfjs-backend-wasm/src/backend_wasm.ts

@@ -210,6 +210,8 @@ export class BackendWasm extends KernelBackend {
 }
 
 function createInstantiateWasmFunc(path: string) {
+  // this will be replace by rollup plugin patchWechatWebAssembly in minprogram's output
+  // and the rest code will be remove by treeshaking
   // tslint:disable-next-line:no-any
   return (imports: any, callback: any) => {
     util.fetch(path, {credentials: 'same-origin'}).then((response) => {