Fix Closure await import mangling regression

src/closure-externs/closure-externs.js

@@ -11,10 +11,6 @@
  * The closure_compiler() method in tools/shared.py refers to this file when calling closure.
  */
 
-// Special placeholder for `await import` and `await`.
-var EMSCRIPTEN$AWAIT$IMPORT;
-var EMSCRIPTEN$AWAIT;
-
 // Don't minify createRequire
 var createRequire;
 

src/closure-externs/modularize-externs.js

@@ -17,3 +17,6 @@ var moduleArg;
  * @suppress {duplicate, undefinedVars}
  */
 var Module;
+
+// Special placeholder for `await`.
+var EMSCRIPTEN$AWAIT;

src/parseTools.mjs

@@ -48,7 +48,10 @@ function mangleUnsupportedSyntax(text) {
     // See also: `fix_js_mangling` in link.py.
     // FIXME: Remove after https://github.com/google/closure-compiler/issues/3835 is fixed.
     if (EXPORT_ES6) {
-      text = text.replaceAll('await import', 'EMSCRIPTEN$AWAIT$IMPORT');
+      // Use a low-precedence `||` pattern so Closure doesn't strip parentheses.
+      // High-precedence placeholders trick Closure into optimizing `(PLACEHOLDER).y`
+      // into `PLACEHOLDER.y`, breaking execution order once swapped back to `await`.
+      text = text.replaceAll('await import', 'EMSCRIPTEN$AWAIT||import');
     }
     text = text.replaceAll('await createWasm()', 'EMSCRIPTEN$AWAIT(createWasm())');
     text = text.replaceAll('await run()', 'EMSCRIPTEN$AWAIT(run())');

test/test_other.py

@@ -467,6 +467,16 @@ def test_esm_worker_single_file(self):
     self.assertContained("new Worker(new URL('hello_world.mjs', import.meta.url), {", src)
     self.assertContained('Hello, world!', self.run_js('hello_world.mjs'))
 
+  def test_esm_worker_closure(self):
+    self.run_process([EMCC, '-o', 'hello_world.mjs',
+                      '-sEXIT_RUNTIME', '-sPROXY_TO_PTHREAD', '-pthread', '-O2',
+                      test_file('hello_world.c'), '--closure=1'])
+    create_file('run.mjs', '''
+    import Module from './hello_world.mjs';
+    await Module();
+    ''')
+    self.assertContained('Hello, world!', self.run_js('run.mjs'))
+
   def test_esm_closure(self):
     self.run_process([EMCC, '-o', 'hello_world.mjs',
                       '--extern-post-js', test_file('modularize_post_js.js'),

tools/link.py

@@ -2129,8 +2129,8 @@ def phase_source_transforms(options):
   save_intermediate('transformed')
 
 
-# Unmangle previously mangled `await import` and `await` references in
-# both main code and libraries.
+# Unmangle previously mangled `await` references in both
+# main code and libraries.
 # See also: `mangleUnsupportedSyntax` in parseTools.mjs.
 def fix_js_mangling(js_file):
   # Mangling only takes place under closure in MODULARIZE mode.
@@ -2140,13 +2140,14 @@ def fix_js_mangling(js_file):
   src = read_file(js_file)
 
   if settings.EXPORT_ES6:
-    # Also remove the line containing `export{};`, which is inserted by
+    # Safely matches 'EMSCRIPTEN$AWAIT' with any amount of surrounding
+    # whitespace around '||'
+    src = re.sub(r'EMSCRIPTEN\$AWAIT\s*\|\|\s*', 'await ', src)
+    # Remove the line containing `export{};`, which is inserted by
     # Closure to mark the file as an ES6 module.
     # https://github.com/google/closure-compiler/issues/4084#issuecomment-1505056519
     # https://github.com/google/closure-compiler/blob/v20260401/src/com/google/javascript/jscomp/ConvertChunksToESModules.java#L111-L113
-    src = src \
-      .replace('EMSCRIPTEN$AWAIT$IMPORT', 'await import') \
-      .replace('export{};\n', '')
+    src = src.replace('export{};\n', '')
 
   src = src.replace('EMSCRIPTEN$AWAIT(', 'await (')