Fix MODULARIZE with sync compilation

ChangeLog.md

@@ -35,6 +35,10 @@ Current Trunk
   modules.  As one side effect of this change it is now required that JavaScript
   functions that are imported by address are now required to have a `__sig`
   specified in the library JavaScript file.
+- `MODULARIZE` + `WASM_ASYNC_COMPILATION=0`, that is, modularize mode but with
+  async compilation turned off, so that startup is synchronous, now returns the
+  Module object from the factory function (as it would not make sense to return
+  a Promise without async startup). See #12647
 
 2.0.8: 10/24/2020
 -----------------

emcc.py

@@ -2841,7 +2841,9 @@ def modularize():
   logger.debug('Modularizing, assigning to var ' + shared.Settings.EXPORT_NAME)
   src = open(final_js).read()
 
-  return_value = shared.Settings.EXPORT_NAME + '.ready'
+  return_value = shared.Settings.EXPORT_NAME
+  if shared.Settings.WASM_ASYNC_COMPILATION:
+    return_value += '.ready'
   if not shared.Settings.EXPORT_READY_PROMISE:
     return_value = '{}'
 

src/settings.js

@@ -954,6 +954,10 @@ var DETERMINISTIC = 0;
 // resolved with the module instance when it is safe to run the compiled code,
 // similar to the `onRuntimeInitialized` callback. You do not need to use the
 // `onRuntimeInitialized` callback when using `MODULARIZE`.
+//
+// (If WASM_ASYNC_COMPILATION is off, that is, if compilation is
+// *synchronous*, then it would not make sense to return a Promise, and instead
+// the Module object itself is returned, which is ready to be used.)
 // 
 // The default name of the function is `Module`, but can be changed using the
 // `EXPORT_NAME` option. We recommend renaming it to a more typical name for a

tests/test_other.py

@@ -4838,6 +4838,31 @@ def test_EXPORT_NAME_with_html(self):
     self.assertNotEqual(result.returncode, 0)
     self.assertContained('Customizing EXPORT_NAME requires that the HTML be customized to use that name', result.stdout)
 
+  def test_modularize_sync_compilation(self):
+    create_test_file('post.js', r'''
+console.log('before');
+var result = Module();
+// It should be an object.
+console.log(typeof result);
+// And it should have the exports that Module has, showing it is Module in fact.
+console.log(typeof result._main);
+// And it should not be a Promise.
+console.log(typeof result.then);
+console.log('after');
+''')
+    self.run_process([EMCC, path_from_root('tests', 'hello_world.c'),
+                      '-s', 'MODULARIZE=1',
+                      '-s', 'WASM_ASYNC_COMPILATION=0',
+                      '--extern-post-js', 'post.js'])
+    self.assertContained('''\
+before
+hello, world!
+object
+function
+undefined
+after
+''', self.run_js('a.out.js'))
+
   def test_export_all_3142(self):
     create_test_file('src.cpp', r'''
 typedef unsigned int Bit32u;