webpack/bundler Fix: Update worker JS file import URL to be compatibl…

…e with bundlers (#22165)

This PR closes #22140 by updating the URL used to import the worker JS
in `library_pthread.js::allocateUnusedWorker`. Previously the URL would
be:
```js
worker = new Worker(new URL(import.meta.url))
```
which webpack translates to the`file:///` path, causing the import to
fail b/c the `file://` path is not valid to access ([webpack docs import
meta](https://webpack.js.org/blog/2020-10-10-webpack-5-release/#importmeta)).

src/library_pthread.js

@@ -447,13 +447,17 @@ var LibraryPThread = {
         var p = trustedTypes.createPolicy(
           'emscripten#workerPolicy1',
           {
-            createScriptURL: (ignored) => new URL(import.meta.url)
+            createScriptURL: (ignored) => new URL("{{{ TARGET_JS_NAME }}}", import.meta.url)
           }
         );
         worker = new Worker(p.createScriptURL('ignored'), workerOptions);
       } else
 #endif
-      worker = new Worker(new URL(import.meta.url), workerOptions);
+      // We need to generate the URL with import.meta.url as the base URL of the JS file
+      // instead of just using new URL(import.meta.url) because bundler's only recognize
+      // the first case in their bundling step. The latter ends up producing an invalid
+      // URL to import from the server (e.g., for webpack the file:// path).
+      worker = new Worker(new URL('{{{ TARGET_JS_NAME }}}', import.meta.url), workerOptions);
 #else
       var pthreadMainJs = _scriptName;
 #if expectToReceiveOnModule('mainScriptUrlOrBlob')

test/common.py

@@ -1150,7 +1150,7 @@ def add_on_exit(self, code):
   #                  libraries, for example
   def get_emcc_args(self, main_file=False, compile_only=False, asm_only=False):
     def is_ldflag(f):
-      return any(f.startswith(s) for s in ['-sEXPORT_ES6', '-sPROXY_TO_PTHREAD', '-sENVIRONMENT=', '--pre-js=', '--post-js='])
+      return any(f.startswith(s) for s in ['-sEXPORT_ES6', '-sPROXY_TO_PTHREAD', '-sENVIRONMENT=', '--pre-js=', '--post-js=', '-sPTHREAD_POOL_SIZE='])
 
     args = self.serialize_settings(compile_only or asm_only) + self.emcc_args
     if asm_only:

test/test_browser.py

@@ -5548,13 +5548,13 @@ def test_error_reporting(self):
   def test_webpack(self, es6):
     if es6:
       shutil.copytree(test_file('webpack_es6'), 'webpack')
-      self.emcc_args += ['-sEXPORT_ES6']
+      self.emcc_args += ['-sEXPORT_ES6', '-pthread', '-sPTHREAD_POOL_SIZE=1']
       outfile = 'src/hello.mjs'
     else:
       shutil.copytree(test_file('webpack'), 'webpack')
       outfile = 'src/hello.js'
     with utils.chdir('webpack'):
-      self.compile_btest('hello_world.c', ['-sEXIT_RUNTIME', '-sMODULARIZE', '-sENVIRONMENT=web', '-o', outfile])
+      self.compile_btest('hello_world.c', ['-sEXIT_RUNTIME', '-sMODULARIZE', '-sENVIRONMENT=web,worker', '-o', outfile])
       self.run_process(shared.get_npm_cmd('webpack') + ['--mode=development', '--no-devtool'])
     shutil.copyfile('webpack/src/hello.wasm', 'webpack/dist/hello.wasm')
     self.run_browser('webpack/dist/index.html', '/report_result?exit:0')

test/test_other.py

@@ -374,7 +374,7 @@ def test_emcc_output_worker_mjs(self, args):
                       test_file('hello_world.c')] + args)
     src = read_file('subdir/hello_world.mjs')
     self.assertContained("new URL('hello_world.wasm', import.meta.url)", src)
-    self.assertContained("new Worker(new URL(import.meta.url), workerOptions)", src)
+    self.assertContained("new Worker(new URL('hello_world.mjs', import.meta.url), workerOptions)", src)
     self.assertContained('export default Module;', src)
     self.assertContained('hello, world!', self.run_js('subdir/hello_world.mjs'))
 
@@ -386,7 +386,7 @@ def test_emcc_output_worker_mjs_single_file(self):
                       test_file('hello_world.c'), '-sSINGLE_FILE'])
     src = read_file('hello_world.mjs')
     self.assertNotContained("new URL('data:", src)
-    self.assertContained("new Worker(new URL(import.meta.url), workerOptions)", src)
+    self.assertContained("new Worker(new URL('hello_world.mjs', import.meta.url), workerOptions)", src)
     self.assertContained('hello, world!', self.run_js('hello_world.mjs'))
 
   def test_emcc_output_mjs_closure(self):