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 +17,7 @@ var moduleArg;
  * @suppress {duplicate, undefinedVars}
  */
 var Module;
+
+// Special placeholder for `await import` and `await`.
+var EMSCRIPTEN$AWAIT$IMPORT;
+var EMSCRIPTEN$AWAIT;

src/parseTools.mjs

@@ -48,7 +48,12 @@ 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');
+      // We must use a low-priority pattern (`void 0 ||`) instead of a normal function name.
+      // Closure treats a normal name like a function call, so it thinks parentheses around it
+      // are useless and removes them (e.g. turning `(PLACEHOLDER).y` into `PLACEHOLDER.y`).
+      // When we swap `await` back in, `await x.y` runs in the wrong order. The `void 0 ||` trick
+      // forces Closure to keep the parentheses safely intact.
+      text = text.replaceAll('await import', 'void 0||EMSCRIPTEN$AWAIT$IMPORT');
     }
     text = text.replaceAll('await createWasm()', 'EMSCRIPTEN$AWAIT(createWasm())');
     text = text.replaceAll('await run()', 'EMSCRIPTEN$AWAIT(run())');

test/test_other.py

@@ -468,6 +468,16 @@ 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

@@ -2126,6 +2126,7 @@ def fix_js_mangling(js_file):
     # 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('void 0||await import', 'await import') \
       .replace('export{};\n', '')
 
   src = src.replace('EMSCRIPTEN$AWAIT(', 'await (')