Fix broken JS glue for AUDIO_WORKLETS with EXPORT_ES6 (#21192)

WASM Audio Worklets with EXPORT_ES6 may break at runtime:

  test.js:989 Uncaught (in promise) TypeError: Cannot set property wasmTable of #<Object> which has only a getter
      at receiveInstance (test.js:989:25)
      at receiveInstantiationResult (test.js:1011:5)

The read-only getter at issue is created in ASSERTIONS-enabled
builds, and conflicts with the current way of exporting wasmTable
on the Module object.

Exporting wasmTable via EXPORTED_RUNTIME_METHODS prevents the getter
from being created in normal builds. In MINIMAL_RUNTIME builds, we
make sure to delete the getter before manually exporting as before.

We also prevent an ES6 Audio Worklet from loading the .wasm binary
via `new URL()`, as `URL` is unavailable in AudioWorkletGlobalScope.

Author: kangtastic

src/postamble_minimal.js

@@ -197,19 +197,19 @@ WebAssembly.instantiate(Module['wasm'], imports).then((output) => {
 #if AUDIO_WORKLET
   // If we are in the audio worklet environment, we can only access the Module object
   // and not the global scope of the main JS script. Therefore we need to export
-  // all functions that the audio worklet scope needs onto the Module object.
-  Module['wasmTable'] = wasmTable;
+  // all symbols that the audio worklet scope needs onto the Module object.
 #if ASSERTIONS
-  // In ASSERTIONS-enabled builds, the following symbols have gotten read-only getters
-  // saved to the Module. Remove those getters so we can manually export the stack
-  // functions here.
+  // In ASSERTIONS-enabled builds, the needed symbols have gotten read-only getters
+  // saved to the Module. Remove the getters so we can manually export them here.
   delete Module['stackSave'];
   delete Module['stackAlloc'];
   delete Module['stackRestore'];
+  delete Module['wasmTable'];
 #endif
   Module['stackSave'] = stackSave;
   Module['stackAlloc'] = stackAlloc;
   Module['stackRestore'] = stackRestore;
+  Module['wasmTable'] = wasmTable;
 #endif
 
 #if !IMPORTED_MEMORY

src/preamble.js

@@ -608,14 +608,14 @@ function instrumentWasmTableWithAbort() {
 #endif
 
 var wasmBinaryFile;
-#if EXPORT_ES6 && USE_ES6_IMPORT_META && !SINGLE_FILE
+#if EXPORT_ES6 && USE_ES6_IMPORT_META && !SINGLE_FILE && !AUDIO_WORKLET
 if (Module['locateFile']) {
 #endif
   wasmBinaryFile = '{{{ WASM_BINARY_FILE }}}';
   if (!isDataURI(wasmBinaryFile)) {
     wasmBinaryFile = locateFile(wasmBinaryFile);
   }
-#if EXPORT_ES6 && USE_ES6_IMPORT_META && !SINGLE_FILE // in single-file mode, repeating WASM_BINARY_FILE would emit the contents again
+#if EXPORT_ES6 && USE_ES6_IMPORT_META && !SINGLE_FILE && !AUDIO_WORKLET // In single-file mode, repeating WASM_BINARY_FILE would emit the contents again. For an Audio Worklet, we cannot use `new URL()`.
 } else {
 #if ENVIRONMENT_MAY_BE_SHELL
   if (ENVIRONMENT_IS_SHELL)
@@ -1000,13 +1000,6 @@ function createWasm() {
 #if ASSERTIONS && !PURE_WASI
     assert(wasmTable, 'table not found in wasm exports');
 #endif
-
-#if AUDIO_WORKLET
-    // If we are in the audio worklet environment, we can only access the Module object
-    // and not the global scope of the main JS script. Therefore we need to export
-    // all functions that the audio worklet scope needs onto the Module object.
-    Module['wasmTable'] = wasmTable;
-#endif
 #endif
 
 #if hasExportedSymbol('__wasm_call_ctors')

test/test_browser.py

@@ -5743,6 +5743,8 @@ def test_full_js_library_strict(self):
     'pthreads_and_closure': (['-pthread', '--closure', '1', '-Oz'],),
     'minimal_runtime': (['-sMINIMAL_RUNTIME'],),
     'minimal_runtime_pthreads_and_closure': (['-sMINIMAL_RUNTIME', '-pthread', '--closure', '1', '-Oz'],),
+    'pthreads_es6': (['-pthread', '-sPTHREAD_POOL_SIZE=2', '-sEXPORT_ES6'],),
+    'es6': (['-sEXPORT_ES6'],),
   })
   def test_audio_worklet(self, args):
     if '-sMEMORY64' in args and is_firefox():

tools/link.py

@@ -1340,9 +1340,12 @@ def phase_linker_setup(options, state, newargs):
       settings.AUDIO_WORKLET_FILE = unsuffixed(os.path.basename(target)) + '.aw.js'
     settings.JS_LIBRARIES.append((0, shared.path_from_root('src', 'library_webaudio.js')))
     if not settings.MINIMAL_RUNTIME:
+      # If we are in the audio worklet environment, we can only access the Module object
+      # and not the global scope of the main JS script. Therefore we need to export
+      # all symbols that the audio worklet scope needs onto the Module object.
       # MINIMAL_RUNTIME exports these manually, since this export mechanism is placed
       # in global scope that is not suitable for MINIMAL_RUNTIME loader.
-      settings.EXPORTED_RUNTIME_METHODS += ['stackSave', 'stackAlloc', 'stackRestore']
+      settings.EXPORTED_RUNTIME_METHODS += ['stackSave', 'stackAlloc', 'stackRestore', 'wasmTable']
 
   if settings.FORCE_FILESYSTEM and not settings.MINIMAL_RUNTIME:
     # when the filesystem is forced, we export by default methods that filesystem usage
@@ -2350,13 +2353,15 @@ def modularize():
       'script_url_node': script_url_node,
       'src': src,
     }
-    # Given the async nature of how the Module function and Module object
-    # come into existence in AudioWorkletGlobalScope, store the Module
-    # function under a different variable name so that AudioWorkletGlobalScope
-    # will be able to reference it without aliasing/conflicting with the
-    # Module variable name.
-    if settings.AUDIO_WORKLET and settings.MODULARIZE:
-      src += f'globalThis.AudioWorkletModule = {settings.EXPORT_NAME};'
+
+  # Given the async nature of how the Module function and Module object
+  # come into existence in AudioWorkletGlobalScope, store the Module
+  # function under a different variable name so that AudioWorkletGlobalScope
+  # will be able to reference it without aliasing/conflicting with the
+  # Module variable name. This should happen even in MINIMAL_RUNTIME builds
+  # for MODULARIZE and EXPORT_ES6 to work correctly.
+  if settings.AUDIO_WORKLET and settings.MODULARIZE:
+    src += f'globalThis.AudioWorkletModule = {settings.EXPORT_NAME};'
 
   # Export using a UMD style export, or ES6 exports if selected
   if settings.EXPORT_ES6: